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DECOMMISSIONING OF OFFSHORE OIL AND

GAS FACILITIES:

DECOMMISSIONING SCENARIOS: A COMPARATIVE ASSESSMENT USING FLOW ANALYSIS

March 2005

Paul Ekins, Robin Vanner and James Firebrace

Part of a wider collaborative study

‘A Methodology for Measuring Sectoral Sustainable Development and its application

to the UK oil & gas sector’

The project is funded under the DTI’s Sustainable Technologies Initiative LINK Programme, with funding from the Engineering and Physical Sciences Research Council (EPSRC), matched by industry, largely through in-kind contributions in

identifying and providing data, case studies and research papers

ACKNOWLEDGEMENTS This report has benefited from the support of a number of organisations, and expertise and input from many people. Our thanks first go to the Engineering and Physical Sciences Research Council (EPSRC), which provided the funding for the researchers at the Policy Studies Institute (PSI) to carry out the work. Similarly, we are grateful to UKOOA, which made the resources available to fund the input of James Firebrace. Decommissioning of offshore structures is a highly complex and technical exercise. In respect of some kinds of structures it is also in its infancy, so that the necessary information to perform the kind of comparison we have attempted was unpublished, hard to find and, sometimes, commercially confidential. Our warm thanks go to the many members of the groups which we convened from the industry to access the necessary documentation and ensure we fully understood what we needed to. We are also very grateful to the group of senior managers from four offshore operating companies (Shell, BP, ENI, and ExxonMobil) who, together with UKOOA and PSI representatives, managed the project. All gave freely of their time when we needed it, although all always had many other things to do. They have given a degree of insight into the industry that we would hardly have achieved otherwise. Our thanks also go to the four highly qualified independent peer reviewers of this report, from whose comments and expertise we have gained great benefit. Having said that, this report is of course our responsibility. While the great majority of the information has necessarily come from the industry, the opinions expressed and the conclusions drawn from it have not. They are ours alone. So too, of course, is responsibility for any errors of fact or judgement which may remain. Paul Ekins, Robin Vanner PSI James Firebrace JFA Consulting March 2005

CONTENTS

1. Introduction..................................................................................................................1 1.1 Methodology – Mapping Material, Energy and Financial Flows................. 1

2. Boundaries, scope and sources.....................................................................................7 2.1 Temporal Boundaries................................................................................. 7 2.2 Spatial Boundary ....................................................................................... 7 2.3 Economic and Fiscal Scope........................................................................ 7 2.4 Scope of the Analysis................................................................................. 8 2.5 Sources for the Analysis............................................................................. 8

3. OPTIONS FOR DECOMMISSIONING...................................................................10 3.1 Introduction to the Issues ......................................................................... 10 3.1.1 Introduction to offshore oil and gas structures .................................. 10 3.1.2 Introduction to regulatory issues....................................................... 10 3.1.3 Decommissioning experience and industrial legacy .......................... 13 3.1.4 Health & safety ................................................................................ 14 3.1.5 Economics of decommissioning ....................................................... 14 3.1.6 Brief description of decommissioning options .................................. 16

3.2 The Reference Scenario ........................................................................... 20 3.3 Top side, Jacket and Footings .................................................................. 21 3.3.1 Energy assessment experience.......................................................... 21 3.3.2 Material, energy and value chain analysis......................................... 22 3.3.3 Footings ........................................................................................... 24

3.4 Pipelines .................................................................................................. 25 3.4.1 Decommissioning scenarios ............................................................. 25 3.4.2 DTI guidelines ................................................................................. 26 3.4.3 Risk to trawling activities ................................................................. 26 3.4.4 Material, energy and value assessment of pipeline decommissioning 27

3.5 Drill Cuttings ........................................................................................... 27 3.5.1 Characterisation of cuttings piles...................................................... 28 3.5.2 Dredging of cuttings scenarios.......................................................... 30 3.5.3 Leaving in-situ scenarios .................................................................. 32

4. Assumptions for the flow analysis..............................................................................35 4.1 Financial expenditure assumptions........................................................... 35 4.2 Material flow assumptions ....................................................................... 37 4.3 Summary Assessment of Material and Energy Flows ............................... 42

5. Non-financial outcomes..............................................................................................43 5.1 Methods of assessing the non-financial outcomes..................................... 43 5.1.1 Clear seabed..................................................................................... 43 5.1.2 Health and safety.............................................................................. 44 5.1.3 Jobs in the UK.................................................................................. 44 5.1.4 Impacts on the marine environment .................................................. 45 5.1.5 Conservation of stocks of non-renewable resources.......................... 47 5.1.6 Impacts of resource extraction .......................................................... 49 5.1.7 Impacts of landfill ............................................................................ 50 5.1.8 Impacts on the fishing industry......................................................... 53 5.1.9 Impacts on fish stocks (and other marine life)................................... 57 5.1.10 Summary of the assessments of non-financial outcomes................... 59

5.2 Evidence for the assessments ................................................................... 60

5.2.1 Clear seabed..................................................................................... 61 5.2.2 Marine environmental impacts ......................................................... 62 5.2.3 Landfill impacts ............................................................................... 63

6. Summary outcomes ....................................................................................................67 6.1 Interpretation of summary outcome matrices............................................ 67 6.2 Summary Outcomes for Topside of Large Steel Structure (see Table 6.1) 68 6.3 Summary Outcomes for Jacket of Large Steel Structure (see Table 6.2) ... 69 6.4 Summary Outcomes for Footings of Large Steel Structure (see Table 6.3) 69 6.5 Summary Outcomes for Entire Large Steel Structure (see Table 6.4) ....... 70 6.6 Summary Outcomes for a Mostly Concrete Structure (see Table 6.5) ....... 71 6.7 Summary Outcomes for pipelines (see Table 6.6)..................................... 72 6.8 Summary Outcomes for drill cuttings (see Table 6.7)............................... 72

7. Assessment of the WIDER APPLICABILITY OF RESULTS.................................82 7.1 Assessment of the generic nature of the large steel structure results.......... 82 7.2 Assessment of the generic nature of drill cuttings pile results ................... 85 7.3 Comparison of Financial Expenditures..................................................... 86 7.4 Comparison of Total Energy Requirement ............................................... 87 7.5 Comparison of Other Non-Financial Outcomes........................................ 88

8. CONCLUSIONS ........................................................................................................90 8.1 Overview of Decommissioning Assessments and Implicit Valuations ...... 90 8.1.1 Total energy requirement (TER)....................................................... 90 8.1.2 Air emissions ................................................................................... 90 8.1.3 Clear seabed and resource conservation............................................ 90 8.1.4 Impact on the marine environment ................................................... 90 8.1.5 UK Employment .............................................................................. 92 8.1.6 Costly scenarios ............................................................................... 92 8.1.7 Covering pipelines ........................................................................... 93 8.1.8 Decommissioning the structure......................................................... 93 8.1.9 Deciding on Drill Cuttings Piles ....................................................... 93

8.2 The Differing Perceptions, Preferences and Priorities of Different Stakeholders ........................................................................................................ 94 8.2.1 A spectrum of views......................................................................... 94 8.2.2 The authors’ assessment ................................................................... 95

8.3 Putting Decommissioning into a Wider Context....................................... 98

9. References.................................................................................................................100 ANNEX 1: THE REGULATORY FRAMEWORK.......................................................105 ANNEX 2: APPROVED DECOMMISSIONING PROGRAMMES ...........................108

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SUMMARY OF METHOD AND CONCLUSIONS

The Purpose and the Method of the Study This report examines decommissioning options for the North Sea, focused on the UK sector, in respect of large steel (considering the topsides, jackets and footings separately) and concrete structures, together with associated pipelines and drill cuttings piles. It is part of a research project under the DTI Link Programme, which is seeking to develop a sustainable development methodology that can be applied to different industrial sectors. The methodology entails using material and energy flow analysis, with their associated financial expenditures, in order to gain insights into the economic, social and environmental implications of various decommissioning options, which the report calls ‘decommissioning scenarios’, because some of the theoretical options discussed are not currently permitted under the North Sea regulatory framework. A reference scenario is adopted in order to have a common comparator for the other scenarios. The reference scenario involves only basic clean up of the topside, and leaving all the material in the structure, pipelines and cuttings in situ offshore. It is stressed that this reference is for the purpose of comparison with the other scenarios only, rather than being in any sense a recommendation or projection of ‘business-as-usual’. By comparing the financial expenditures of a particular scenario with the reference scenario, an implicit valuation can be obtained of the non-financial outcomes associated with that scenario, were it to be adopted by society. Because of the tax arrangements in the UK sector of the North Sea, between 30% and 70% of decommissioning expenditures could end up being paid by the UK taxpayer because of taxes foregone. In the numerical estimates below, the taxpayer contribution is taken to be 50% for the sake of simplicity, but it could be more or less that this depending on the particular tax circumstances of different fields. Care is taken in the scenarios to compare them on the basis of equivalent material endpoints. For example, the scenarios which envisage removal to shore of part or all of the structure end up with large quantities of recovered metal to be recycled. For the scenarios which envisage that this material is left offshore, account is taken of the material and energy flows which would be required to replace it by producing the same amount of metal from virgin sources. The material, energy (with associated air emissions) and financial flows for the scenarios are quantified using data from the industry, some of which is available on websites from the results of life-cycle analyses, some of which has only recently been generated and is as yet unpublished. A method is developed and presented for the qualitative assessment of non-financial outcomes from the scenarios, including: a clear seabed, health and safety, UK employment, marine environmental impacts, conservation of stocks of non-renewable resources, the impacts of resource extraction, impacts of landfill, impacts on the fishing (specifically trawling) industry, and impacts on fish (and other marine life). The method entails assigning symbols, in the manner sometimes used for environmental impact assessment, ranging from + + + to - - -, to the possible ranges of outcomes across the different dimensions in the different scenarios. This information, much of which is quite complex, is presented in summary

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matrices, from the entries in which the various scenarios can be compared across the different dimensions. Because decommissioning, for some types of installation at least, is still in its infancy, much of the information in the report is taken from a few industry case studies, most importantly what is called Case Study A, relating to a large steel structure. This is the only detailed information for the decommissioning of such structures that is available, across the range of issues studied. An assessment is made of the extent to which the conclusions from this case study are likely to be applicable to the UK sector of the North Sea more generally. It is shown that the Case Study A structure is in fact in the middle of the range of large steel structures in the North Sea UK sector and that, while there are no doubt special factors that apply more or less to it alone, there is no obvious reason why this should bias the results in one direction or another. Within the bounds of error of the results generally, the results from Case Study A are taken to be broadly representative of large steel structures in the North Sea as a whole. It is less likely that these results could be validly applied to structures either much smaller or much larger than Case Study A, as other factors may then become relevant which might lead to non-linear relationships between, for example, cost and mass. It was not possible to explore the possibility of such relationships in the project.

The Conclusions from the Study The information from the summary matrices is presented in an overview table, from which conclusions are drawn. Because the information in the case studies used for this study may not be fully representative of the structures to be decommissioned in the North Sea generally, the results and conclusions from this study should be regarded as illustrative rather than definitive. While it is believed that the conclusions that follow are robust, in general terms at least, they are derived from much complex scientific and technical material, which is discussed in more detail in the text, and which provides further context for the interpretation of the conclusions. The conclusions should be read with awareness of this context and, especially, the limitations of the data that it reveals. The headline results of the study may be summarised as follows:

• Energy use: it makes a difference to scenarios’ relative energy performance if account is taken of the energy needed to replace materials left offshore.

• Air emissions: offshore diesel use is more emission-intensive than onshore refining, so that even those scenarios which use less energy overall than the reference, because of savings from recycling, may produce more emissions if they entail more offshore activity.

• Clear seabed and resource conservation: taking recyclable metals to shore for recycling conserves resources and reduces the impacts of resource extraction which would otherwise be necessary to replace them; taking non-recyclables to shore produces potentially considerable negative environmental impacts from landfilling; re-injecting non-recyclables (e.g. drill cuttings) prevents landfill impacts, but is energy-intensive, and can be logistically problematic and entail increased safety risks.

• Impact on the marine environment: compared to the reference, all the scenarios (except those for drill cuttings) have a negative impact on the marine

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environment, though in most cases the impact is only of medium or small scale and is short-lived. For drill cuttings, preferable options for the marine environment to leaving them in situ are covering, re-injection, or removal to shore, though these options all have their own problems with respect to other environmental impacts and/or feasibility on the scale envisaged, and are expensive.

• UK Employment: decommissioning expenditures may benefit UK communities if carried out in areas with unemployment and appropriate skills; however, the study has been unable to quantify these benefits.

• Costly scenarios: the most expensive of the scenarios assessed in detail involve the return to shore of a large mainly concrete structure, and of drill cuttings; there are large environmental costs as well as benefits associated with these scenarios (especially if the drill cuttings have to be landfilled); the assessment suggests that they offer least environmental value for money of all the scenarios considered. The bioremediation or re-injection of drill cuttings are also expensive, but have fewer environmental drawbacks. Bioremediation is not currently being considered as a practicable option in the UK context.

• Covering cuttings and pipelines: these scenarios generate benefits for the trawling industry, but have a number of negative environmental impacts and are relatively expensive. Covering drill cuttings piles would improve the seabed over its current condition.

• Decommissioning the structure: the scenarios that involve removal of materials to shore achieve a clear seabed, conserve the stock of resources, reduce the resource extraction to produce from virgin sources the material that has been recovered, and benefit the trawling industry through opening up areas to trawling; on the negative side, their health and safety implications, and their impacts on the marine environment and in terms of landfill are worse than the in-situ scenarios, which also tend to benefit fish rather than the trawling industry; they are also more expensive.

The Differing Perceptions, Preferences and Priorities of Different Stakeholders

A spectrum of views

There are many differences in perceptions, preferences and priorities involved in the issue of decommissioning, which is one of the reasons why there is unlikely to be a full social consensus on the ‘best’ decommissioning scenario. In fact, there are at least seven different kinds of consideration which will influence the attitude to decommissioning of different stakeholders: technical feasibility, safety, cost, environmental impacts, the regulatory framework, reputation and the political environment. The assessment in this study shows that the environmental outcomes from the various decommissioning scenarios are mixed. No scenario can be said to be definitively superior from an environmental point of view. The total removal scenarios can only be justified environmentally if a relatively high value is put on a clear seabed, benefits to the trawling industry, the conservation of the stock of resources (because of recycling) and the impacts of resource extraction (which are avoided because of the recycling). The latter two considerations do not apply to drill cuttings, the material from which must either be landfilled or converted into an inert construction material.

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In addition, implementing the removal scenarios would imply that a relatively low value is put on energy use and air emissions (for the concrete structure and drill cuttings), landfill (for all the removal scenarios), and impacts on the marine environment and fish (for all the removal scenarios except for drill cuttings). The judgement over drill cuttings is made more complex in that it is the only leave in situ scenario which is worse for the marine environment than alternative scenarios (which, however, have other negative environmental impacts). It is not clear that the relative valuation accorded to these issues either by the range of environmental groups concerned about the marine environment, or by society more widely, would favour total removal. It is also not clear what action might be most in line with the precautionary principle. Avoiding the negative environmental impacts from the removal scenarios may be as important in this regard as achieving a clear seabed and recycling metals, none of which can be regarded as scarce. One advantage of the removal scenarios from the point of view of the industry is that they remove any future liability that might otherwise arise from materials left in situ. The authors’ overall assessment

Recognising that views and values concerning the different issues involved vary across different stakeholders, the authors have arrived at the following overall assessment on the basis of the evidence presented in the study. For the topside, all parties seem agreed that removal to shore is the only scenario worthy of serious consideration, and the assessment shows this to have fewer environmental trade-offs than some other removal scenarios. It still involves expenditure of some £30m (£15m from the taxpayer) for a single large steel structure, some £12m more than the shallow disposal scenario. For the jacket, the same arguments seem to apply, except that the difference in cost between the removal and shallow disposal scenarios is significantly less. The footings are a different matter, largely because of their difficulty of removal, causing both environmental impacts and safety concerns, the former of which are complicated by the footings’ interaction with drill cuttings. The major impact of leaving them in situ is on the trawling industry. With a total cost of removal for the UK of nearly £1 billion (one half of which would be paid by UK taxpayers), it is not clear that the removal of footings offers good value for money. Unlike the large steel structure as a whole, there are strong arguments, environmental and financial, for not removing large concrete structures to shore, and few environmental arguments for doing so. The taxpayer expenditure alone on this scenario (£143m) would not seem to be justified by the benefits that would result. For drill cuttings the judgement is more complex, with the environmental benefits of achieving a clear, and ecologically regenerating, seabed, having to be assessed against the environmental impacts and financial costs of the scenarios concerned. On the basis of current technologies, perhaps a light covering over the drill cuttings piles, with continued exclusion of trawlers, might be the favoured option of those for whom the continued existence of the uncovered drill cuttings piles is unacceptable. If re-injection, bioremediation and drill cuttings processing techniques were to improve, then perhaps these options for removal would become favoured. For the present, however, the combination of environmental and financial considerations seems to favour leaving the cuttings in situ.

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For large pipelines (small ones are not difficult to remove) the situation is similar to that for footings. Recovering them clears the seabed, conserves resources and reduces the impacts of resource extraction, but with some environmental impacts and probably some safety risks, and involves considerable cost. The main beneficiaries of this expenditure, as with clearing footings, would be the trawling industry. Covering the pipelines is even more expensive and has little environmental justification over removal. Leaving them, with remedial action to make them safe for trawling if necessary, would be the preferred scenario, unless a very high value was put on a clear seabed and the resources they comprise. All scenarios with material left in situ would require monitoring, the financial and (small) environmental implications of which need to be added to the relevant scenarios. The financial calculations would need to include the costs of any remedial action (for example, to pipelines, which monitoring revealed to be necessary). Responsibility for monitoring, and for taking action on any information that it might generate, would also need to be considered. This raises the possibility of this monitoring being combined with marine monitoring for other purposes. Broadening the context beyond decommissioning

Decommissioning is not the only activity in the marine context with environmental implications. Indeed, according to OSPAR, the offshore oil and gas industry is not responsible for any of the six human pressures on the marine environment to which it gives a Class A (highest impact) grading. Three of the six pressures come from fishing. One response to marine environmental degradation, and the loss of fish stocks, has been proposals to establish marine protected areas (MPAs). OSPAR itself is currently engaged in efforts to complete by 2010 a joint network of well-managed, ecologically coherent MPAs, although these are much smaller than the fishing-free zones that would be necessary to have a significant conservation effect on fish stocks. This simultaneous concern with decommissioning and MPAs, and current efforts to put in place an overarching EU Marine Strategy, offers a significant opportunity to develop an approach to marine environmental protection that embeds decommissioning into a wider framework of marine environmental protection, which includes the regeneration of fish stocks, which could combine into a single programme the monitoring effort that would be required for both MPAs and to keep under surveillance any materials for offshore oil and gas operations that were to be left offshore. Such an approach could also support the resolution of long term liability issues related to any material left in situ.

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1. INTRODUCTION

This report has been written as part of a collaborative study carried out under the DTI’s Sustainable Technologies Initiative LINK programme and funded by the Engineering and Physical Sciences Research Council (EPSRC): ‘A Methodology for Measuring Sectoral

Sustainable Development and its application to the UK oil & gas sector’. The overall objective of the study is to develop a generic sustainable development methodology that can be applied both to the oil and gas industry and to other regions or sectors – and thus be of wider public benefit. This methodology is based on an analysis of material and energy flows and their related financial implications down the value chain, coupled with an environmental impact analysis. The study as a whole will cover four issues of importance to the offshore oil and gas sector: decommissioning, produced water, energy efficiency and employment. This report describes the application of the methodology to and the conclusions on decommissioning.

1.1 METHODOLOGY – MAPPING MATERIAL, ENERGY AND FINANCIAL FLOWS

Sustainable development is a process the assessment of which involves the simultaneous consideration of environmental, economic and social performance. The mapping of material, energy and financial flows is intended to cast light on the environmental and economic dimensions, because many environmental impacts arise from the flow of materials and energy, and financial flows are obviously intrinsic to the economic dimension. Material and energy flow analysis is based on the fundamental principle that neither energy nor matter can be created or destroyed, only changed from one form into another. The analysis involves drawing a conceptual boundary around a system and undertaking an accounting process for energy and/or material flows through the system or across its boundary, balancing inputs, changes in stocks and outputs of a given material, or a flow of energy, over a given timeframe. The idea is simply illustrated in Figure 1.1. Materials cross the boundary of the system under consideration and are transformed by a process. Those that stay within the boundary are added to the material stocks of the system. Those that leave the boundary (whether as products or wastes) are subtracted from the material stocks of the system. Figure 1.1 shows the mass balance equation expressing the reality that matter cannot be created or destroyed. The energy part of Figure 1.1 shows that typically the process under consideration in the system will use high-grade energy and transform it into low-grade energy which will usually be dissipated across the boundary of the system. Like matter, the amount of energy will be conserved but it will be changed from a high-grade to a low-grade form.

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Figure 1.1 - Conceptual mass and energy flow diagram

Where for materials within the boundary: Inputs = Products + Wastes + (Stocks(t=1) - (Stocks(t=0))

Industrial processes are typically like those in Figure 1.1, utilising high-grade energy and raw materials to produce a higher value product, and one or more low-value waste products, often themselves requiring further processing. This further processing (of which decommissioning is an example) itself may produce low-value wastes and involve environmental impacts. Assessment of such processes needs to consider

• The impacts and environmental risks of the waste if left unprocessed;

• The value and environmental burden of the input materials used in the processes and the outputs from it; and

• The wider social and distributional implications of these outcomes including the interests of future generations.

Any perceived net benefit has to be considered in relation to the financial expenditure of the processes and the overall benefits they yield. Implications for the Methodology of Decommissioning of Offshore Structures

The various options for decommissioning offshore structure are described in some detail later in this report. Here it may just be noted that such decommissioning adds a further factor to be considered in the methodology to be used here, as there is potential to recycle the materials comprising the structure. In essence, the two broad decommissioning options are to return the structure to shore and recycle the materials which comprise it, or to leave it in situ. Not recovering and processing the structure requires that raw material and energy be consumed to replace the materials which would have been recycled if the structure had been brought onshore. The key material and energy considerations of the different approaches to decommissioning are therefore:

Process

Inputs

Products

Wastes

Material system boundary

Stocks

Process

High-grade

energy inputs

Low-grade

energy outputs

Energy system boundary

Where for energy within the boundary: Inputs = Outputs (high grade becomes low grade)

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• In situ: the energy, emissions and input material requirement to replace the materials which would have been recovered if the structure had been dismantled and taken to shore;

• Return to shore: the energy and material used to dismantle the structure and take it to shore (mostly diesel in marine vessels) and the energy (and therefore emissions) used to recycle the material back to a usable form.

The energy requirements of decommissioning of offshore structures are documented by the Institute of Petroleum (IP 2000). This provides a methodological framework as well as default values for companies making an assessment of energy use in the absence of case specific figures being available. This framework is used as the starting point for this analysis of decommissioning both for energy (diesel) and its corresponding material flows. There is a further potential approach to the analysis of the implications of leaving the structure in situ. The energy, material and financial implications of stimulating extra recycling of an equal amount of already existing onshore materials, rather than the implications of replacing them from virgin sources, could have been considered. This would have the added benefit of conserving raw materials, by not requiring new extraction of such materials to take place. Any such approach would have to estimate the full implications of recycling waste materials which are not currently recycled. Such recycling could be expected to be more difficult, costly and energy-intensive than the recycling currently carried out, because the materials which are easiest to access are those which are recycled first. This study has been unable to consider this approach, because the necessary detailed analytical work does not appear to have been carried out, and it was certainly outside the scope of this project. If it emerges from this study that the difference between stimulating extra recycling and extracting new resources is likely to be a significant factor in deciding between decommissioning options, then a further study could be undertaken to investigate these differences in detail. Material Values and Endpoints

The financial flows involved in any process consist of the financial costs of undertaking the process. There are also various non-financial values related to the process’s material and energy flows. For example, the conservation value of recovering material through decommissioning has to be weighed against the resource cost of the diesel required to recover the material and the negative value of any waste materials such as emissions and non-recyclable materials which have to be landfilled. Key considerations for the methodology here are:

• Replacement of material left in situ is only required to be considered in the methodology if the material would have been recycled in the event of a return to shore option being followed. If the materials are not economically recoverable after the structure has been dismantled onshore, the energy and value within the materials has been fully ‘used’ in the commissioning stage of the structure’s value-chain.

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• The possibility of re-use of the structure without full material reprocessing needs to be considered, and could well be beneficial as it avoids the energy required in the recycling process. In this case the material and energy benefits are those of the material and energy which would have been required to build the structure which the materials are going to replace. Examples of such re-use would be the use of a crudely cut structure as a quay (some parts of Brent Spar were used in this way) or the potential use of disused oil pipelines for the transport of CO2 for carbon sequestration. Figure 1.2 provides a high view of the material flows for different options, and indicates how the analysis of a re-use option could be undertaken. This diagram shows the actual material and energy flows (solid lines) and the ‘virtual’ material and energy flows (dashed lines), which would have been required, in the absence of recovery, to achieve the same material endpoint.

Figure 1.2 Equivalent Material Endpoints from In Situ and Recovery

Decommissioning Options

• Temporary steel work is often required in the decommissioning of large structures and therefore becomes part of the structure to be decommissioned. In common with the rest of the structural steel work, the material endpoint of this temporary steel work will be recycled steel (or replaced steel if left offshore). Therefore, in respect of temporary steel work the analysis does not include the energy and financial expenditures required to generate the raw steel. It does however include the energy and costs of fabricating the temporary steelwork from raw steel for the purpose of carrying out the decommissioning.

Non-financial outcomes

There are social and environmental implications of the decommissioning of offshore structures, the latter of which may be associated with the material and energy flows. These implications, which will not necessarily be included in any way in the financial flows associated with material and energy use, need to be addressed explicitly. The approach taken

In-situ structure Recovered structure Offshore Recovery

Replacement process

Recovered Material

Landfilled Material

Alternative Use

Equivalent use process

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in this study is not to make a valuation of such non-financial outcomes, but to identify, inform and qualitatively assess the importance of them relative to some reference case. A further intention of the study is to provide an implicit valuation of these non-financial outcomes and benefits by highlighting the additional expenditures required to achieve them, relative to the reference case. How they are assessed in this study is discussed in detail in Sections 4 and 5. The non-financial outcomes (including the material and energy flows) to be assessed are, in no particular order:

Assessed quantitatively (see Section 4)

1. Material inputs; 2. Material endpoints (of the material being decommissioned); 3. Total energy requirement (TER); 4. Total gaseous emissions; 5. Financial expenditures;

Assessed qualitatively (see Section 5)

6. A clear seabed; 7. Health and safety of personnel directly involved in the decommissioning process; 8. Jobs in the UK; 9. Impacts on the marine environment; 10. Conservation of non-renewable resources; 11. Impacts of resource extraction; 12. Impacts of landfill; 13. Impact on the fishing (specifically trawling) industry; and 14. Impacts on fish (and other marine life).

In the discussion of these issues that follows, any financial considerations related to the issues are given numerically where possible, while the non-financial components are given different symbolic representation, which is explained in Section 5. Because of the uncertainties involved in some of the financial calculations (which relate to processes some of which have never actually been carried out), it would have been desirable to give the financial estimates as ranges. Usually, however, this was not possible from the extant sources. It should, therefore, be borne in mind that point financial estimates are not intended to suggest accuracy or levels of uncertainty, but simply reproduce the numbers in the studies consulted. The conclusions from this tentatively drawn in order to reflect the high level of uncertainty in the assessments overall. As noted by Greenpeace (2004), which of all the environmental groups has taken most interest in and exerted most influence on the decommissioning issue, any full consideration of decommissioning also needs to take account of broader issues such as “the established international trend against dumping”, “the cumulative damage and the potential precedent that could be set by dumping individual installations on a ‘case-by-case’ basis”, the need for industry to take responsibility for the products it creates, the precautionary principle and the need to protect the environment from harm. Some of these issues will be qualitatively

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assessed under the headings above. Others will be brought into consideration in the concluding discussion and interpretation of the results of the analysis in Section 8. Structure of the Report The next section of this report describes the boundaries of the analysis, the scope of the impacts being considered and the sources for the more detailed analysis which follows. Section 3 investigates the various options for decommissioning and chooses a number of these for further study. Section 4 sets out various issues and assumptions related to the calculations of the energy, material and financial flows for the chosen options. Section 5 describes the assessment methodology for the various non-financial outcomes listed above. Section 6 then presents the information from the analysis in the form of summary outcome matrices with a descriptive commentary. Section 7 discusses the extent to which the data available and analysed, which is for only a few North Sea structures, is representative more widely of North Sea structures in the UK sector which are to be decommissioned. Section 8 then presents some conclusions from the analysis and, in particular, the implicit valuation of the different decommissioning options which have been studied, were they to be chosen by society. As noted above, these conclusions are presented in the context of a broader discussion of social values, not least because this is the context in which any decisions about decommissioning will actually be taken.

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2. BOUNDARIES, SCOPE AND SOURCES

The temporal, spatial and economic boundaries, the scope of the analysis undertaken here, and the impacts it identifies, and the sources for the data that underpins the analysis, are now discussed in turn.

2.1 TEMPORAL BOUNDARIES

The temporal boundary of the analysis is defined by the start and end times of the decommissioning options chosen:

• The start of the analysis is after shutdown and all the required tasks which are common to all decommissioning options. These include shutdown, well decommissioning and flushing and cleaning of tanks, process equipment and pipelines.

• The end of the analysis is defined by the material endpoints of all the decommissioned and input materials.

o For leave in-situ options, it is envisaged that the monitoring and surveying of all in-situ material is ongoing. The financial liability from any ill effects from this material is included in the summary outcome matrices, although not quantified, because in the absence of any clear specification of these effects it has not been possible to estimate them.

o For the recovery option, this will be when the material has been returned to its recycled and usable form, or treated as waste and financial liability has been transferred to a third party (typically a landfill site owner).

o For all decommissioning options, the end point of the fuel inputs is the gaseous emissions of CO2, SO2 and NOx only. Methane (CH4) emission factors are not available for the onshore processing of metals and these emissions are therefore not included in the analysis.

There is no limit to the time period over which the impacts (and non-financial outcomes) of decommissioning are in principle considered relevant for this study.

2.2 SPATIAL BOUNDARY

There is some uncertainty whether the recovered material would remain within the UK or even within Europe, although current legislation requires certain waste streams to be dealt with in their country of origin. Similarly the impacts of decommissioning may occur inside or outside the UK. Therefore the spatial boundary of the analysis is not restricted to the UK and is defined by the earth’s outer atmosphere. This very wide definition of the spatial boundary of the analysis allows the between-country distributional implications of the impacts to be considered.

2.3 ECONOMIC AND FISCAL SCOPE

This analysis only looks at the financial expenditures incurred in decommissioning and does not assess quantitatively the wider economic impacts. Significant non-financial outcomes,

8

which may have economic implications, are identified and qualitatively assessed relative to the reference case (see Section 5). Decommissioning expenditures should be viewed as normal industry capital and operating expenditures. However, because of the tax regime applied to offshore oil and gas operators in the UK sector of the North Sea, it is also the case that, because decommissioning expenditures can be offset against tax liability in the normal way, some proportion of them can be regarded as effectively public expenditure (because of the tax revenues foregone). This is identified as an important, but little appreciated, distributional implication of decommissioning, which makes decommissioning relevant to public as well as private spending priorities, and this point is stressed in what follows. However, quantitative assessment of the wider fiscal implications of the decommissioning options (for example, considering the sources of alternative tax revenues required due to such tax offsets) is beyond the scope of this study. When assessing the value of material flows, the market value of material endpoints is provided. This does not however capture the entire value of this endpoint to society. For example, the gate fee charged to landfill material does not fully capture the impacts of the landfill on local people or the reduced opportunity future generations have to use the land in the way they wish. These wider and non-financial outcomes are considered separately as part of the non-financial component of the assessment.

2.4 SCOPE OF THE ANALYSIS

The analysis includes the material, energy and financial implications of the transportation, dismantling and processing of structural materials. Therefore, the analysis for a removal decommissioning option will include:

• The diesel requirements of all ship and lorry transport from the offshore site to a landfill/smelting facility;

• The material, energy, financial, emission and other implications of dismantling the structure;

• The energy and emission implications of smelting the metallic material from the structure.

For options that leave the structure offshore, the analysis includes the material, energy and financial implications of so doing, plus the implications of producing the same endpoints in terms of useful material onshore, as discussed above.

2.5 SOURCES FOR THE ANALYSIS

Decommissioning of offshore structures in the North Sea is in its relative infancy. Relatively few structures have so far been decommissioned. No large fixed steel structures have so far been decommissioned. It is not surprising that, to date, the great majority of study and analysis of the impacts and different options of decommissioning have been carried out by the industry. In fact, this

9

study would not have been possible had the industry not given access to the project researchers information from industry sources, which had not been previously available. Much of this information comes from recent intensive work relating to the decommissioning (which is still in its pre-consultation phase) of a large steel structure which is here called Case Study A. Two other bodies of work have provided useful material for this study:

• Studies relating to the decommissioning of Maureen, a steel-based re-floatable platform structure. (Phillips UK 1999)

• Studies relating to the decommissioning of Ecofisk I, a planned 15-year decommissioning programme for thirteen steel platform facilities as well a storage tank in the Norwegian North Sea. (ConocoPhillips 1999). For ease of reference in some tables, this has sometimes been called Case Study B.

• The UKOOA-led Joint Industry Project (JIP), a major programme of research seeking the best way of tackling the historical legacy of accumulated drill cuttings beneath offshore installations in the North Sea (UKOOA 2002).

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3. OPTIONS FOR DECOMMISSIONING

3.1 INTRODUCTION TO THE ISSUES

This introductory section tackles a number of general issues associated with decommissioning. Three subsequent sections tackle the principal components of decommissioning offshore oil and gas facilities in more detail. These are:

• Decommissioning of the topside, jacket and footings (Section 3.3);

• Decommissioning of pipelines (Section 3.4); and

• Tackling the piles of drill cuttings at the foot of structures (Section 3.5). Section 3.2 discusses the issues related to the choice of a reference case against which the chosen decommissioning options can be compared. 3.1.1 Introduction to offshore oil and gas structures Figure 3.1 shows what Watson (2001, p.27) calls a typical North Sea deep-water platform. The structure consists of:

• A ‘topside’, the actual platform above the surface of the sea on which offshore activities take place.

• A ‘jacket’, a structure largely of tubular steel which supports the topside.

• ‘Footings’, the lowest and heaviest section of the jacket, which are considered separately for decommissioning purposes. The footings include ‘pile clusters’ to aid piling of the structure into the seabed, and a drilling template, through which the wells are drilled.

• A pile of ‘drill cuttings’ on the seabed beneath the platform, consisting of drilled rock particles and drilling fluids arising from drilling the wells.

Figure 3.1 gives some details and dimensions of this ‘typical’ structure. 3.1.2 Introduction to regulatory issues More detailed information about the regulatory framework for decommissioning is given in Annex 1. In this section material is only included if it is immediately necessary for the understanding of the decommissioning options that are to be assessed. The regulatory framework for the decommissioning of offshore structures in the North Sea is provided by the OSPAR treaty. There is currently a presumption under the OSPAR convention that all offshore structures will be entirely brought to shore for decommissioning, with only limited possibilities for derogation. In particular, OSPAR Decision 98/3 (taken in 1998) requires the following:

• All topsides of all structures are to be removed and brought to shore for reuse, recycling or disposal;

11

• All sub-structures or jackets weighing less than 10,000 tonnes must be totally removed and brought to shore for re-use, recycling or disposal;

• For sub-structures weighing over 10,000 tonnes, there is a presumption to remove totally but with the potential of a derogation being agreed on whether the footings might be left in place; and

• Derogation may be considered for the heavy concrete gravity based structures as well as for floating concrete installations and any concrete anchor-base.

12

Figure 3.1: Typical North Sea Deep Water Platform Source: Watson 2001, p.27

13

At the UK level, the DTI’s Guidance Notes for the decommissioning of offshore facilities and pipelines detail how all components of the decommissioning process should be dealt with including drill cutting piles and pipelines (DTI 2001). The regulatory regime with regard to the approval procedure is a two/three-stage process. The first stage consists of submission to the DTI of a first draft of a proposal setting out how the operator intends to decommission the installation with supporting evidence as to how the different elements of the proposal were decided on. Then there is a process of dialogue between the operator and the DTI until a revised second draft, including an Environmental Impact Assessment, can be published and opened for public consultation. However, the DTI guidelines make clear that stakeholder dialogue should be taking place in advance of the publication of the second draft. Any OSPAR derogation requires formal international consultation and is to be undertaken by the relevant government. In the case of UK regulated waters, the relevant governmental body would be the DTI. The studies relating to Case Study A were commissioned by an operating company as part of the process of preparing the first draft of the submission to the DTI of proposals to decommission a large steel structure. 3.1.3 Decommissioning experience and industrial legacy There has been a range of structures of various types which have either been decommissioned or have been approved for decommissioning. A list of these structures is provided in Annex 2. As noted in the previous section, much of the content of this report is based on a number of studies commissioned to inform planned decommissioning programmes concentrating on larger structures, including:

• Brent Spar –A steel floating storage facility;

• Maureen – A steel-based re-floatable platform structure;

• Ekofisk I – A planned 15-year decommissioning programme for thirteen steel platform facilities as well as a storage tank;

• Case Study A – A large steel structure such as that illustrated in Figure 3.1. Actual decommissioning of Brent Spar and Maureen and the assessment outcomes of the Ekofisk structures are shown in Table 3.1.

Table 3.1 Examples of Actual Decommissioning Carried Out or Agreed

Installation component Maureen1 Brent Spar2 Ekofisk I3

Topside

Jacket Onshore Onshore Onshore

Footings Re-floated – onshore - -

Tank - Onshore In-situ

Pipelines Leave buried Outstanding Leave buried

Cuttings In-situ (with review) - In-situ 1 Decommissioning involved removing the whole structure to shore for re-use or recycling, but leaving the pipelines and drill cuttings in situ. 2 This outcome followed the unsuccessful attempt by Shell in 1995 to dispose of Brent Spar at sea. 3 This plan for decommissioning has been approved by the Norwegian authorities but has not yet been completed. Sources: Maureen: Phillips UK 1999, Brent Spar: Parmentier 1998, Ekofisk: ConocoPhillips 1999.

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None of the 33 large fixed steel structures on the UK Continental Shelf (UKCS) has yet been decommissioned. Many of these larger structures will be eligible for derogation under the current OSPAR arrangements and could apply to leave their jacket footings in-situ. Table 3.2 lists all the various types of structures on the UKCS. The extent to which the data for Case Study A is typical of other large steel structures is discussed in Section 7.

Table 3.2 The Number of Each Type of Platform on the UKCS (2001)

Type of platform1 Number

Small steel 196

Large steel 33

Concrete gravity based structure 11

Floating production facility 22

Steel self-elevating production jack-up 1

Steel tension leg platform 3

Total 266

Source: DTI 2002, Annex 2A, p.44. 1 While the broad thrust of this classification is widely accepted, the industry might classify somewhat differently some of the less common structures

3.1.4 Health & safety The decommissioning of offshore structures poses significant health and safety challenges, even for an industry accustomed to managing high-risk offshore operations. Estimates are made on the statistical probability of serious and fatal accidents occurring during the decommissioning process. For example, the Ekofisk I planning process estimated that the Potential Loss of Life (PLL) of decommissioning the structure (all 13 jackets and the tank) was 8% (i.e. there was an 8% probability of a fatal accident) for the largely in-situ scenario, and 29% for the total removal decommissioning scenario (ConocoPhillips 1999, p.19). However, these figures are summations of risk over extensive and diverse operations, some of which may be particularly risky, while the total risk may not be higher than the permitted risk in comparable industrial activities in other sectors. It may therefore be more appropriate to consider these risks individually for particular operations in relation to the thresholds accepted for these other activities, rather than summing them over the whole operation. This may be especially important when the different decommissioning options have different quantities of man-hours involved, as well as varying distributions of risk. 3.1.5 Economics of decommissioning Cost of decommissioning

Figure 3.2 shows the estimated cost of decommissioning all of the structures associated with the UKCS. It shows that the cumulative cost of total removal was an estimated £8.4 billion in 2001, which had increased in real terms to £8.8 billion by 2002. Watson (2001, p.6) estimates that the costs of total removal of the North Sea structures (i.e. also including Norwegian and Dutch structures) may be £13-£20 billion. This illustrates the enormous economic uncertainties still associated with decommissioning, especially of the large steel structures in deep water, of which there is as yet no experience. Moreover, while the structures may be similar, they are not identical, and differences in detailed design, coupled with differences in

15

the nature and extent of wear and tear over their lifetimes in the harsh North Sea environment, mean that the decommissioning of each one will need to be approached on a fresh basis.

Figure 3.2 The Cumulative Costs of Decommissioning from Two Surveys

Fiscal regime The governmental contribution to the decommissioning of UK offshore structures via tax relief will be between 30-70% depending on historical levels of Petroleum Revenue Tax (PRT) paid1. Based on present cost estimates, the cost to the taxpayer of decommissioning all of the structures on the UKCS associated with oil and gas is estimated to be £4.6 billion in the years 2001-2030 (Kemp et al 2001, p.31, medium exploration scenario), though clearly it could be higher if the higher cost estimates presented in the previous section are closer to the outcome. On average, therefore, current estimates would seem to be that the UK taxpayer’s contribution towards the total cost of decommissioning through lost tax revenues will be about 50% of the total cost. Residual liability

All those with a financial interest in an oil and gas installation have a residual liability for anything left in-situ. In the event of the ownership being passed on, perhaps to new entrants and smaller operators (DTI 2001, p.34), new owners may be asked to give financial security to old owners, because, in the event of new owners going out of business, liability can revert to former owners. Under the Petroleum Act 1998, a party with relevant interests in an

1 This compares with the Norwegian Government paying two thirds of the cost of decommissioning the Ekofisk structures, and a potential Government contribution of up to 80% in other cases, depending on the past tax treatment of the companies concerned (Osmundsen & Tvetarås, p.1584)

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offshore installation may be obliged to submit and carry out a decommissioning programme, and ultimately be individually liable to do so even in the event of others in the partnership defaulting (joint and several liability). If a party wishes to end their liabilities in the asset, this will only be agreed to by the Government if appropriate external financial security is agreed within the partnership (DTI 2001, Annex F). However, financial liability of decommissioning activities and the material endpoints of materials brought to shore is largely passed over to contractors as the materials are returned to the wider economy. In addition to formal legal liability, residual materials may be a potential liability in terms of reputation, for a certain time and for the larger oil companies at least.

3.1.6 Brief description of decommissioning options The detailed assessment of decommissioning options in this report is based on case studies that have been available to this project for this purpose. The extent to which these case studies may be taken as broadly applicable to a large range of the structures found on the UK Continental Shelf (UKCS) is discussed in Section 7. The case studies considered relate to: 1. Large steel production platforms which are fixed to the seabed with jackets of greater than 10,000 tonnes (based on a case study of a structure in the middle of the size range of large steel structures);

2. Large mostly concrete structures (based on a tank case study); 3. Pipelines, based on a case study which looked jointly at an oil and at a gas pipeline of sufficient size for decommissioning not to be straightforward;

4. Large drill cuttings piles of about 40,000 tonnes with some cuttings containing oil-based drilling muds.

A large part of the analysis in this report focuses on large steel structures, based on data for a particular structure, here identified as Case Study A, which contains approximately the amount of materials set out in Table 3.3:

Table 3.3 Materials Contained in a Mid-Size Large Steel Structure1

Totals Steel Aluminium Copper Non-metals

t t t t t

Topside 20,520 20,000 20 200 300

Jacket 10,200 9,000 500 700

Footings 11,300 10,000 300 1,000

Total structure 42,020 39,000 820 200 2,000

1 It should be noted that the tonnages of materials in such structures will vary and these figures should be regarded as no more than indicative of the kinds of masses involved.

The purpose of this report is to present a comparative analysis of the possibilities for decommissioning of various offshore oil and gas structures which have come to the end of their useful lives. It is assumed that a thorough investigation of the various possibilities will have been undertaken within the oil and gas sector and this report is largely based on the results of these investigations.

17

The range of decommissioning options for oil and gas structures in general can be briefly described as follows:

• Leave in situ – Leaving the structure in situ after the cleaning of all hydrocarbons. While leaving individual component parts of the structure (e.g. topside, jacket etc.) can be considered separately, obviously lower components have to be left in situ for this to be considered for a higher component.

• Monitoring – Leaving the structure in situ with a programme of on-going monitoring of the fate of the abandoned structure and associated materials (e.g. pipelines and drill cuttings piles).

• Toppling – Doing the minimum required to topple the structure so that it simply lays on its side at the site.

• Shallow disposal – Dismantling the structure and depositing it onto the seabed around the site of the operational structure.

• Deep-sea disposal – The removal and transport and of the structure for depositing at a deep ocean disposal site where it would be effectively impossible for there to be any further human interaction with the material comprising it.

• Recovery – The removal and transport to shore, and dismantling and re-processing or landfilling, of all the components of the structure.

In the North Sea, not all these options are legal, and therefore currently relevant to the industry in practice under the present regulatory framework, an issue that is discussed further in Section 3.2. Apart from this issue, three of the above options have not been analysed further in the report, for the following reasons:

• Monitoring – Appropriate monitoring will need to be part of any option that leaves any materials in situ, and it has therefore been included in the discussion of the options that envisage this, rather than considering it as a separate option.

• Toppling – There has been no or very little work done on this option relevant to the larger steel structures being analysed in this report. Piper Alpha was toppled on safety grounds after a serious explosion and fire made the structure unusable and dangerous. These circumstances would make any data from the event of little more general use. If it was discovered to be a technically feasible option for fixed steel structures, toppling would have many similarities to the shallow disposal option but with moderately lower material, energy and financial requirements. It would also have very similar non-financial outcomes.

• Deep-sea disposal –There has been little work done on this option since the OSPAR regulations made it effectively illegal, making it rather difficult to provide accurate analysis of its cost and material basis. As discussed in Section 3.3, deep-sea disposal is considered to have a significantly greater total energy requirement than shallow disposal (154% of the toppling option), without having additional benefits, and it is therefore excluded from further analysis on these grounds. This does not prevent future analysis of the option using this methodology if it was later felt that there were benefits unique to such an approach to decommissioning.

Table 3.4 presents an overview of the various decommissioning options considered later in this report. For all of them, the assumption is that basic clean up (of hydrocarbons from the

18

structure’s oil and gas systems), well decommissioning and the clearing of debris from the immediate surface of the seabed (i.e. not including the drill cuttings pile) will be undertaken separately to decommissioning. Therefore these activities are not further considered here. The ‘Leave in situ’ options for the structure (T1, J1, F1, CON1) assume that nothing else is done beyond these activities. Options T2, J2 involve shallow disposal of the structure. T3, J3, F2, and CON2 entail recovery of the structure and its removal to shore for reprocessing or disposal of its constituent materials. Option F2 (recovery of footings) has two possible variants (F2a & F2b) depending on whether

• F2a: the drill cuttings are left in place

• F2b: the drill cuttings are removed. This is important as the removal of the footings with the drill cuttings left in situ could disrupt the drill cuttings with resulting release of hydrocarbons into the water column. This difference will be apparent in the description of the approach to drill cuttings rather than in the description of F2 itself. ‘Hybrid’ options would be to cut the footings at the level of the drill cuttings, which then might or might not be covered; or to dredge (using a suction dredge) only those cuttings round the footings, so that the footings could then be removed. The dredged cuttings could then be disposed of as discussed below, and the rest left undisturbed, or covered, as desired. Because of lack of data, these options have not been explored in detail, but they will be considered in the relevant place in the conclusions in Section 8.

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Table 3.4 Summary of Decommissioning Options

Decommissioning Options Structure type

Structure Component

Leave in situ

Shallow Disposal

Recovery

Rem

edial action

Bury pipelines

Excavate & leave

cuttings

Cover cuttings

Excavate & cover

cuttings

Re-inject

cuttings onsite

Re-inject cuttings

off-site

Rem

ove and treat

cuttings onshore

Topside T1 T2 T3

Jacket J1 J2 J3 Large

fixed steel Footings F1 F2(a, b)

Concrete Tank CON 1 CON 2

Pipelines P1 P2 P3 P4

Drill Cuttings C1 C2 C3 C4

Note: Only unshaded boxes contain options that are considered in detail below, for reasons that are given in the text

There is little problem with removing small pipelines to shore, and only decommissioning of larger pipelines is considered here. Pipelines may be left in situ (P1), recovered and removed to shore (P2), subjected to ‘remedial action’ (P3), which entails carrying out additional activities (which might include a combination of: mechanical trenching, burying with sand or rock, or removal and recovery of selected lengths of pipelines) to ensure long-term integrity of the pipelines (Case Study A, ENV 02, p.16) or buried (P4). These options are all described in more detail in Section 3.4. With regard to drill cuttings, these may be left in situ (C1), covered (C3, with or without the lowest part of the footings left in situ, as noted above) or removed and treated onshore (C4). One further possible process for their removal is referred to as ‘excavation’. This entails subjecting the drill cuttings pile to a low velocity, high volume flow of water which raises it into suspension. Re-suspended material is dispersed into the surrounding water and carried from the site with the prevailing current or tide and redeposited over a much larger area. Following excavation, the site of the pile may be left (C2) or an attempt could be made to cover the much larger area over which the cuttings have been deposited. However, this latter option is not further considered here, because it would require an impracticable volume of sand and gravel (estimated to be more than 8 million tonnes of sand and gravel combined). Other options for drill cuttings are their re-injection into a well, at the same or a different site. Some information on the re-injection of cuttings is presented below, but it is not one of the options analysed in detail in this report, because it was not assessed in relation to Case Study A and the available data relating to it is therefore not comparable to the data that has been used for the other options. However, it will be assessed more generally as an option where appropriate.

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By referring to Section 3.1.2 and Annex 1, it will be noted that not all the decommissioning options to be analysed in subsequent sections are currently permitted under the OSPAR regulatory framework. In particular, T1,2 and J1,2 are not permitted under this regulatory framework. They are therefore at present only theoretical, rather than available, options for the North Sea and the rest of the OSPAR area. It is at least part of the purpose of policy analysis to investigate the outcomes and implications of current regulatory practices to see whether they appear to be appropriate. This is the reason why currently prohibited decommissioning approaches have been included in the analysis of this project, despite their only theoretical application to the OSPAR area. It is hoped that the results of the analysis may be useful in ongoing discussions on the OSPAR regulatory framework, or in relation to the regulation of other offshore oil and gas producing areas.

However, it is also important that analysis of this kind should not be misunderstood, especially in an area as politically sensitive as that of decommissioning. Because the rest of this report is focused exclusively on the North Sea area, the various decommissioning approaches to be analysed will be called ‘scenarios’ rather than options, to emphasise that their inclusion in this analysis does not imply either that they are currently available approaches for the industry (which some of them obviously are not) or that they necessarily should be available options. Some insights as to their desirability or otherwise may emerge during the course of the analysis, but certainly no assumptions are being made about this in advance.

3.2 THE REFERENCE SCENARIO

As noted above the purpose of this study is to compare, using flow analysis, various decommissioning scenarios in respect of their material, energy, financial, environmental and other non-financial outcomes. Such a comparison needs to be made against a common reference scenario. Two factors seem important in the choice of such a scenario. First it should be the analytically logical choice. If the purpose of the methodology being employed is to enable comparisons to be made between the outcomes of the different scenarios, then the important thing from this perspective is that the reference scenario is the best in terms of the transparency with which it allows the comparisons to be made. Second, the reference scenario should be as little as possible open to misunderstanding and misinterpretation. While in fact the choice of a reference scenario says nothing at all about this scenario’s desirability, this may not always be perceived to be the case. In particular, choosing the current North Sea regulatory framework as the reference may, from different perspectives, be seen as an attempt either to reinforce or undermine it. Similarly, choosing a different position from among the range of perceived possible alternatives may be seen as making some statement about the desirability of the current regulatory position or about the alternative being considered. From an analytical point of view, the reference scenario should provide a common baseline on which all the other scenarios can build. This then ensures that their outcomes can be

21

compared in as direct a way as possible, without having to add or subtract different elements in order to arrive at comparable positions. From an interpretative point of view it is desirable that the reference scenario is clearly an analytical construct so that it is obviously differentiated from those decommissioning approaches which may be perceived as possible social choices. The reference scenario which has been chosen for this study is the starting point from which any decommissioning takes place i.e. the structure (comprising the topside, jacket and footings), pipelines and drill cuttings have only had the basic clean-up and clearance of the surrounding area as described above. The structure, pipelines and drill cuttings themselves are ‘left in situ’, with no further monitoring or maintenance, and this is how the term ‘leave in situ’ should be understood in what follows. This is not an option that is being proposed by any of those who are involved in the debate about North Sea decommissioning. Moreover, owners of rigs are not likely to be willing to accept ongoing liability for an un-maintained structure which would eventually topple as the structure disintegrates. Furthermore, because total topside clean-up would not be practical offshore2, leaving the topsides in situ would ultimately lead to the depositing of hazardous materials into the marine environment, most noticeably asbestos3. For all these reasons the reference scenario chosen here is not, and should not be interpreted as, a realistic decommissioning scenario. It is simply a reference for the purpose of comparison between other scenarios. However, it is not necessarily the case (as is recognised by the current regulatory framework) that some parts of the structure (e.g. the footings) or other materials involved in decommissioning (e.g. the pipelines and drill cuttings) could not be left in situ as part of decommissioning. Where a scenario envisages that any materials are left in situ, the implications for the ongoing monitoring of these materials will be discussed under the scenario concerned.

3.3 TOP SIDE, JACKET AND FOOTINGS

3.3.1 Energy assessment experience The Institute of Petroleum’s guidelines for the calculation of estimates of energy use and gaseous emissions in the decommissioning of offshore structures (IP 2000) considers the direct energy in the recovery process as well as the energy used by other sectors to replace the materials not recovered. The results of an assessment which includes the energy requirement for replacing the material are shown in Table 3.5. The report by Environment and Technology Ltd. (ERT 1997) took toppling as its baseline scenario, because it had the lowest overall energy requirement of all the decommissioning scenarios considered there. Table 3.5 shows that with the exception of the complete deep-water disposal scenario, the total energy required for the decommissioning scenarios are

2 Industry sources, decommissioning interest network meeting of November 28th, 2003. 3 Industry estimates are that the ongoing maintenance of an abandoned topside would range from £1.5 - £5m per annum.

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comparable and within 14% of the baseline scenario and within the uncertainty surrounding the energy requirement assessments (ERT 1997, p.10).

Deep-sea disposal of steel structures (originally proposed for the decommissioning of Brent Spar) was revealed by the ERT study as the most energy-requiring scenario. Table 3.5 shows its energy requirement to be 154% of the toppling (baseline) scenario if total energy requirement is considered, including the energy requirement of replacing the materials not recovered. Given that the extra energy requirement was greater than the estimated 30-40% uncertainty in the assessment, deep-sea disposal of such structures was therefore shown by these figures to be more energy-intensive than other scenarios. It should however be noted that this result should not be applied directly to the Brent Spar case, because Brent Spar differed greatly from the structures being considered here in that it contained a high proportion of concrete and was a floating structure. It is important when considering assessment of decommissioning scenarios that the level of scenario development is considered. For example, the original assessment of scenarios for Brent Spar decommissioning (1994/5) compared the relatively developed deep-sea disposal scenario, with the mostly unknown conceptual scenario of onshore disposal (Brindley 1997).

Table 3.5 Comparative Energy Costs For Various Decommissioning Scenarios for

Steel Structures

% of Total energy

(Compared with toppling as baseline)

Scenario Replace-

ment

Recycling Direct Marine

Support

Total

Toppling (Baseline) 53 9 16 22 100

Partial ashore and partial in-situ 37 17 16 31 101

Partial removal with partial in-situ and creation of reef in other location

59 5 17 25 106

Complete removal ashore 11 29 21 53 114

Complete removal to deep water 58 7 21 68 154 Source: ERT 1997, Page 11 table 4 Note: Only the partial ashore/partial in-situ and the complete ashore scenarios are permissible under current OSPAR regulations

3.3.2 Material, energy and value chain analysis The analysis of offshore structures in this paper uses flow analysis, following the materials through the decommissioning process, and looking at the energy inputs and the value of the materials as their location and composition change through the recovery process. The analysis to consider the energy requirement of decommissioning includes energy inputs such as fuel used in support ships and cutting material, as well as the energy required to replace the materials not recovered. Table 3.6 shows the kind of figures that could be used in such a calculation.

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In material flow analysis, a mass balance methodology is used to ensure that the sum of the material inputs are accounted for in the outputs. This approach is paired with energy and value chain analysis so that an assessment can be undertaken as to the value of the product and waste material outputs, relative to the value of the material and energy inputs.

Table 3.6 Energy Requirement for Metal and Recycling Processes

Production Recycling from scrap

Metal GJ/T

(IP 2000, Table

6)

(ERT 1997)

GJ/T

Page

number

(ERT

1997)

GJ/T

(IP 2000,

Table 8)

(ERT 1997)

GJ/T

Page

number

(ERT

1997)

Standard steel 25 20 5 9 10 6

Low alloyed steel 32 - - 9 - -

High alloyed steel 56 - - 9 - -

Aluminium 215 215 6 15 14 6

Copper 100 58 7 25 30 7

Zinc 65 - - 10 - -

General Approximately 15% of material designated for recycling will prove unsuitable. 11

Sources: IP 2000 & ERT 1997

For illustration, if a simplified example of whether to leave in-situ a single tonne of steel from an offshore location is considered, the materials outcomes of the two basic decommissioning scenarios, excluding associated fuels and emissions and assuming that 15% of materials are not recoverable, are:

� In-situ = 1 tonne on seabed + the raw materials associated with the generation of 0.85 tonnes of steel (e.g. iron ore)

� Recovery = 0.15 tonnes of steel landfilled + 0.85 tonnes of recovered steel Therefore the leave in situ scenario needs to consider the additional generation of 0.85 tonnes of steel onshore. The energy requirements in the two scenarios would be (adapted from IP 2000):

� In-situ = energy required to generate 0.85 tonnes of steel replacement � Recycle = retrieval energy for 1 tonne of steel + energy required to recycle 0.85 tonnes of steel + energy required for the landfill of 0.15 tonnes.

The total energy requirement (TER) is the total energy required to return the materials to the common material endpoint of the scenarios. Therefore, if the (retrieval energy + landfill energy) < 8.5 GJ [0.85*(20-10) (assuming ERT 1997 figures)], then in energy terms at least it would make sense to bring the structure onshore for recycling. The value outcomes associated with such material flows would be:

� In-situ = the value of the in-situ structure (Possible financial benefits such as increase in fish stocks due to a fishing exclusion zone, less the market valuation of residual liability)

� Recycle = market value of 0.85 tonnes of recycled steel

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The value of the landfilled steel is assumed to be zero as it no longer has any use and there has been a financial transfer (the gate fee) associated with the transfer of liability and therefore of any required monitoring. There will however be a non-financial (negative) value associated with the impacts of landfill, which is not fully captured in the gate fee. This non-financial component includes the value of the loss of landfill void space to future generations, due to the additional landfill in the recovery scenario.

The 85% rate of recovery used in the example is merely used to illustrate the point. In reality this picture would be far more complex with each of the various material flows having different material and financial outcomes with different degrees of recoverability. The rate of recovery of each material will be determined by what form the materials are in, as well as the relative value of the material. For example, steel is used as a structural material and will therefore be in a relatively pure form and therefore have a high rate of recovery. Copper on the other hand, may well be dispersed within wires and therefore might have a relatively poor rate of recovery, if it were not for its relatively high value. If there are parts of the structure being re-used for purposes other than as oil or gas facilities, the savings in energy and materials required to replace the materials used in the re-use have to be considered carefully. For example, if parts of a structure are cut-up and used as a quay or as sea-defence, the energy, materials and value which could be attributed to such a structure would be equal to the energy materials and value of a structure which would most likely have been built for such a use in the absence of the re-used materials. 3.3.3 Footings For sub-structures weighing over 10,000 tonnes (out of the water), there is a possible derogation from the OSPAR Convention’s principle of removal of all structures from the sea. Footings are defined as the jacket below the highest point of the piles. This derogation was introduced as many of the large steel structures typical on the UKCS were not designed with removal in mind, and there was some doubt about the technical feasibility and health and safety implications of doing so. Under the terms of the derogation, it is the OSPAR member country that is responsible for conducting a multinational stakeholder consultation for a derogation to be granted. Once the footings have been cut and lifted onto a ship or barge, the material and energy flow implications of decommissioning the footings can be considered in a similar way to the topside. However, the energy used in association with cutting the footings including any support ships would be included in the analysis. Any footings left in-situ would still need to leave 55 metres below low-water surface level to ensure safe navigation as set out in the International Maritime Organisation (IMO)’s Guidelines (see Annex 1). This requirement would therefore override the footings removal derogation offered under OSPAR (although footings of a size to be eligible for derogation are most unlikely to be in shallow water). There is a further complication when the decommissioning of the footings is being considered, concerning their interactions with the cuttings piles. Many of the cuttings piles settled around the footings as they were discharged from the installation during drilling operations. If it were decided to leave the cuttings pile in-situ, some, disturbance of the cuttings piles would be inevitable when cutting the footings from the seabed (in a worst case

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scenario 100% of the cuttings could be dispersed into the surrounding water and re-settle over an area of several hectares, see Table 5.6). However, it was found to be possible to remove the cuttings around the in-situ footings during the dredging trials around North West Hutton (UKOOA 2002, Final Report, p.21, Q.53). Another possibility is to cut the footings where they meet the cuttings pile with little disturbance to the pile more generally. The interaction between footings and cuttings piles may therefore be summarised as follows:

• If it were decided to remove the cuttings piles, this would be technically feasible whether or not the footings were being removed.

• The footings could be accessed and removed by only removing the cuttings immediately around them, thereby avoiding considerable disturbance of the cuttings.

• It would be possible to cut the footings at the level of the cuttings pile, leaving the residual footing in the cuttings pile, which might or might not then be covered, and removing the rest of the footings to shore.

These interactions between the footings and cuttings piles need to be borne in mind when decommissioning scenarios for the footings and cuttings piles are being considered. The technical challenges of all these operations, involving the cutting, excavation and removal of large quantities of metals and others materials from the deep seabed, should not be underestimated. Given that it has never yet been undertaken, there is obviously the possibility of unforeseen complications and consequent economic (for example, in respect of costs), social (for example, in respect of health and safety) and environmental (for example, in respect of disturbance of the cuttings piles) impacts. There is some evidence that at present the structure acts as refuge for fish and habitat for cold-water coral, something that is discussed in more detail in Section 5.1.4. This effect would obviously cease if the structure were to be removed and fishing in the area were to be resumed (there is currently a 500m radius fishing exclusion zone around structures). However, if left in-situ, the footings could pose a hazard to trawler fishing, and this would probably prevent extensive trawling activities around the in situ footings. In the absence of the footings the cuttings piles are more likely to be disturbed by trawler fishing activities. The implications of disturbing the cuttings piles would be the potential release of oil-based contamination into the marine environment.

3.4 PIPELINES

At present the decommissioning of pipelines is not regulated by the OSPAR Convention. A framework for the decommissioning of offshore pipelines is provided under the 1998 Petroleum Act, and safety issues are covered by the 1996 Pipeline Safety Regulations (DTI 2002, par 10.1). The decommissioning of pipelines is considered case by case based on comparative assessments of all scenarios. As noted above, small pipelines are removed fairly easily to shore, so that it is only the decommissioning of larger pipelines that is considered here. 3.4.1 Decommissioning scenarios Important issues when assessing the decommissioning scenarios for oil and gas pipelines are whether the pipeline is presently trenched or covered, and if so, the status of the coverings and the prospects of the pipelines being uncovered in the future. This is important as exposed

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pipelines can pose a risk to trawling operations. As discussed above (see Section 3.1.6) the potential scenarios available are: 1. leave in-situ (P1); 2. leave in-situ and undertake remedial action including partial selective burial, covering or removal to reduce the risk to fishing activities (P3);

3. trench and bury (P4); and 4. recover and take to shore (P2). If recovery of pipelines is desired, for smaller pipelines this can be effected relatively easily in a reverse process to that which laid them. This is by turning the pipeline around a very large reel on the same type of vessel which laid the pipeline (AURIS 1995, page 5.12). For less flexible pipelines, they may be cut and made buoyant and towed to shore, or cut and lifted onto a vessel (AURIS 1995, page 5.12). 3.4.2 DTI guidelines The DTI decommissioning guidelines (DTI 2001, pp.26, 27) set out the decision-making framework for the consideration of the decommissioning of individual pipelines:

• all feasible decommissioning scenarios should be considered and a comparative assessment made;

• any removal or partial removal of a pipeline should be performed in such a way as to cause no significant adverse effects upon the marine environment;

• any decision that a pipeline may be left in-situ should have regard to the likely deterioration of the material involved and its present and possible future effect on the marine environment;

• pipelines can be left in-situ if due to structural damage or deterioration or for other causes they cannot be recovered safely and efficiently; and

• account should be taken of other uses of the sea. 3.4.3 Risk to trawling activities An important potential impact of leaving any pipeline in-situ is the risk posed to the trawler fishing fleet. A modelling exercise (AURIS 1995) was undertaken to try to estimate the number and type of interactions with pipelines if all of the pipelines on the UKCS were decommissioned by leaving them in-situ. The results of the assessment, shown in Table 3.7, combines the modelled number of interactions with any pipeline (based on 1983 amounts of fishing and assumed random fishing patterns) with estimates of the deterioration of the decommissioned pipelines.

Table 3.7: Estimated Number of Interactions1 Between Fishing Gear and Pipelines

Per Year

Year 10 Year 30 Year 50

Any part of pipeline 36,000 36,000 36,000

Exposed sections 15,000 14,000 13,000

Spanning sections 500 1,200 1,300

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Section with a break1 20 50 140

Source: AURIS 1995, p.6.28 1 ‘Interaction’ in this context includes passage over buried as well as unburied pipelines. 2 As the pipelines age, decay and rust, breakages in the pipelines could occur, potentially leaving jagged edges.

It is important to note that by no means all interactions between fishing gear and pipelines result in any noticeable impact. Indeed, only broken sections (or spanned sections which are broken during the interaction), or very large uncovered pipelines could plausibly lead to a snagging incident and therefore pose a safety hazard. It is also useful to put these interactions in context with snagging hazards posed by and interactions with offshore objects, most noticeably wrecks. These are shown in Table 3.8.

Table 3.8: Estimated Number of Interactions Between Fishing Vessels and Other

Objects on the Seabed

Object Potential interactions per year

Operational submarine cables 26,000

Wrecks 48,000 (likely to be more)

Pipelines 36,000

Source: AURIS 1995, p. 6.28

3.4.4 Material, energy and value assessment of pipeline decommissioning The material, energy and value assessment of decommissioning pipelines is similar in form to the assessment of the decommissioning of main structures. The key difference is that the in-situ scenario may have significant material demands, if the pipeline is to be covered with rocks (scenario P3). A 36” pipeline would need to covered by 0.5 metres of rocks, which would require a pile 3 metres either side and therefore an estimated 4,000 m3 of material per kilometre (AURIS 1995, page 5.14). A further consideration is the relatively dispersed nature of pipelines, and whether the material, energy and value benefits of recovering such dispersed material justifies the material, energy and financial cost associated with such recovery. No energy analysis of the decommissioning of pipelines can be found in the literature.

3.5 DRILL CUTTINGS

Drill cuttings piles are created by solid waste discharges onto the seabed during well-drilling operations. Historically, the drilling muds used in the drilling process were oil based and therefore the cuttings have hydrocarbon contamination, as well as often containing traces of heavy metals, PCBs and radioactive material from the bed and cap rock. It is estimated that there are 1.3 million cubic metres of cuttings accumulated on the North Sea seabed of the UK and Norwegian continental shelves (Wills 2000, p.59). Research undertaken in this area includes a research programme commissioned by UKOOA (UKOOA 2002), which carried out a number of case studies, the most significant of which were around the North West Hutton, Beryl A and Ekofisk 2/4A structures, in order to identify the best available techniques and best environmental practice (BAT and BEP) for these cuttings. Gerrard et al. (1999) also investigated as a case study the North West Hutton pile which, with a volume of 25,225m3 and a mass of 42,126 tonnes, is one of the larger piles.

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The report, UKOOA 2002, is presented in question-and-answer format. The four main decommissioning scenarios considered by the report were: I. Dredging of the cuttings with offshore processing; II. Dredging of the cuttings with onshore processing; III. Covering and leave in-situ with monitoring; and IV. Leaving in-situ with monitoring.

Table 3.9: Energy Requirement and Cost Estimates for Cuttings Piles Management

Strategies

Strategy

number

Description Estimated energy Estimated cost

Related

scenario GJ per m3 Page,

Question

numbers

£ per m3 Page,

Question

numbers

Component

of I & II

Dredging of cuttings

(no treatment)

Required

for C4 0.07 20,50 300 20,49

IA Re-injection of slurry (Total)

1.8 22,58 550-1,200 22,57

IB Enhanced bioremediation (Total)

122 17,30

2,650-5,000

17,31

IIA Landfill cuttings (Total) ~0.1 20,50 550 23,70

IIB Onshore treatment of cuttings (Total)

C4 6.7 23,66 ~1,500 23,65

III Covering in-situ C3 5 19,44 240-1,000 19,43

IV Leave in-situ C1 with monitoring

negligible 16,21 25-100 15,20

Source: UKOOA 2002

Table 3.9 shows the energy requirements and cost estimates for the different scenarios. Not surprisingly, no treatment at all of the cuttings (IV) requires the least energy and entails the lowest costs (as the only operation required would be monitoring). Next in energy requirement is dredging and landfilling the cuttings, which costs five to twenty times as much as leaving them in situ. Re-injection of the drill cuttings requires more energy, and covering the cuttings in situ, or treating them onshore, requires more energy still, with re-injection and onshore treatment being more expensive than the landfill scenario. Easily the highest requirements, in terms of both energy and cost, are associated with the bioremediation scenario. The next sections discuss the nature of drill cuttings piles and the decommissioning issues raised by them, in more detail. 3.5.1 Characterisation of cuttings piles There is an estimated 1.3 million cubic metres of cuttings piles in the North Sea as a whole (Wills 2000, page 59, par 1). Gerrard et al. (1999, p.8) estimate that “the total inventory of hydrocarbons in cuttings piles is similar to the annual input into the North Sea from all sources”. It is estimated that the oil in the 6 largest oil-based mud piles represents 24% of the total mass of oil in piles in the UK. An important finding of the sampling stage of the

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UKOOA study was that the cuttings piles are highly heterogeneous both in shape and content. However, the study was able to provide an indication of the nature and impacts of legacy as it stands. Task 2B of the UKOOA drill cuttings study (UKOOA 2002) assessed the environmental impacts of oil-based mud (OBM) and water-based mud (WBM) drill cuttings piles. The independent Scientific Review Group (SRG) for this study regarded this Task 2B as “a well-executed study”, and noted and appeared to endorse its findings: “The results indicate that the present effects of existing piles are highly localised, and the spatial extent of the areas affected is a small percentage of the total [UKOOA 2002 actually showed it to be about 1,000 km2 on the UKCS out of the total North Sea area of about 700,000 km2, which may be compared with the 130,00-370,00km which is estimated to be trawled annually – UKOOA 2002, Task 2B, p.2]. The total quantities of hydrocarbons in the piles are substantial (about 150,000 tonnes), but these are largely immobilised and are only being removed very slowly by erosion, degradation and leaching (over several or many decades). The rate of release to the wider environment is therefore small in relation to the amount of hydrocarbons from other sources (e.g. rivers).” (SRG 2002, p.8)

Water column and food chain impacts

Much of the evidence for impacts of the present cuttings pile is based on laboratory based work. However, surveys carried out at the cuttings piles around Case Study A found the presence of PAHs and PCBs at greater concentrations than their relevant Ecological Assessment Criteria (EAC), where EACs are defined as the concentration of a substance in the marine environment below which no harm to the environment or biota is expected (Case Study A, ENV05, p.17). These concentrations of PAHs and PCBs therefore represent theoretical risks of harm, extrapolated from known toxic concentrations. Also, octyl and nonyl-phenols were found at relatively high concentrations close to the platform. These are thought to have oestrogen-mimicking effects, and there have not so far been any ‘no-harm’ safety threshold concentrations set for these chemicals (Case Study A, ENV08, p.20). It will be important to ascertain whether these potentially harmful concentrations of toxic chemicals are found around other drill cuttings piles. Task 2C of the UKOOA drill cutting research programme (UKOOA 2002) was designed to investigate the water column and food chain impacts of drill cuttings piles, using a laboratory-based bioaccumulation study, sediment analysis and toxicity testing. The bioaccumulation study utilised an artificial ecosystem (mesocosm) representing the sediment (either OBM drill cuttings material or reference North Sea sediment) and overlying water. However, the report stated: “It should be stressed that the laboratory toxicity tests are not directly analogous to the in-situ conditions. In particular it may be noted that the laboratory tests investigate disturbed sediment which is not necessarily the case in the field. A further point to note is that a vast volume of seawater overflows the cuttings piles in the field situation; therefore a negligible proportion of this overall volume will come in contact with the cutting material” (UKOOA 2002, Task 2C, Executive Summary).

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The key findings of the UKOOA (2002) Task 2C study were broadly reassuring, finding that none of the concentrations of potentially toxic substances (including PAHs [polyaromatic hydrocarbons], metals, endocrine disruptors and NORM [Naturally Occurring Radioactive Material]) appeared likely to result in an adverse effect on biota; that there was no incremental bioaccumulation effect through the water column or through the sediment with OBM versus reference sediment; that there was no biomagnification of the PAHs, heavy metals, or NORM; and that there was no bioaccumulation in the fish species studied (turbot), perhaps because due to the action of their known detoxification systems. There was a toxic response in the OBM (but not WBM [water-based mud]) sediments, relative to the reference sediment, but it seemed likely that this was due to a ‘smothering’ effect from the total hydrocarbon content (THC) rather than any physiological effects from the contaminants. The toxicity results also indicate that the potential for water column effects, albeit on a very minor scale in volumetric terms, exist if the OBM sediments are disturbed. The Scientific Review Group (SRG) for the UKOOA (2002) study was not uncritical of the way the Task 2C study had been carried out. It considered that the finding “that hydrocarbons tend to be assimilated by but not accumulated in the organisms” to be “not surprising”, but also considered that, in respect of other contaminants, “further longer term and/or in situ experiments will be required to resolve the matters satisfactorily” (SRG 2002, p.9), where ‘the matters’ here refer to food chain contamination. This issue is referred to again in connection with Case Study A in Section 5.1.4. 3.5.2 Dredging of cuttings scenarios Strategies I and II as listed above rely on the dredging of the drill cuttings from the cuttings piles. The favoured technology for this was found to be suction dredging the material. The result of this is a slurry containing solids and seawater that would need to be dealt with using strategies as described in the following two sections. The ratio of sea water to cuttings varied greatly during the trials undertaken around North West Hutton. Ratios of 10:1 to 20:1 water to solids were typically experienced (UKOOA 2002, Final report, Q46, p.19). It is believed that, if operated in a real-life situation, further experience of the process, and its continuous operation, would enable these ratios to be reduced. During the dredging, there was little evidence of pollution of the water column beyond the ‘immediate plume’, and no discernible impact at a distance of 100m (UKOOA 2002, Final report, Q.48 p.20). There was however re-suspension during back washing of the suction tube during times of blockages. The study also concluded that the cuttings could be removed from around the footings whether or not these were going to be left in situ. Strategy I – Offshore processing:

A. Re-injection of slurry – minimal treatment of the slurry to permit the re-injection into an existing or dedicated well. Gerrard et al. (1999. p.10) found re-injection to have the lowest environmental impacts of any disposal scenario, but acknowledged that on a large scale it might be slow, and suffer from logistical difficulties. It might also increase energy use and atmospheric emissions. In addition, this scenario may not presently be permitted

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(UKOOA 2002, Q.58, p.55) under the OSPAR convention due to the more general restrictions on the dumping of waste at sea.

B. Enhanced bioremediation of cuttings (UKOOA 2002, Task 5a, p.51) relies on several reactor vessels on the seabed with a supply of oxygen, bacteria and warm water, from support operations either on the associated installation or a ship. The liquids would be lifted to the surface and treated before being discharged offshore. The solids would be re-deposited on the seabed after bioremediation. Gerrard et al. (1999, p.9) did not consider that offshore bioremediation was practicable, but technology might have made it more so in the interim. However, as noted above, this is a very costly scenario and requires by far the largest consumption of energy (122 GJ per m3 compared to the next highest scenario which is onshore treatment which requires 6.5 GJ per m3). Moreover, the process would only operate in the summer, and could take 5 years for a 6,000 m3 pile and some 20 years for some of the larger piles. (UKOOA 2002, Final report, p.18) It is not impossible that, in the longer term, technological developments may reduce some of these obstacles to bioremediation.

Both re-injection and enhanced bioremediation therefore face serious practical constraints at the present time, which is why they have not been considered in the detailed practical assessment in Section 6. However, were these constraints to be reduced or removed through technological advances, and were their relatively high cost to be considered justified by their environmental benefits, then they could become worthy of serious consideration, and this is noted in Section 8. Strategy II – Onshore processing These scenarios rely on the shipping to shore of either the liquefied slurry, or alternatively just the solids if the water can be separated and treated offshore. The scenarios are:

A. Landfill of solids with minimal processing – this offers the cheapest and simplest of the onshore strategies both in terms of energy and cost. At present, there is only one landfill site licensed to receive oily solids (Stoney Hill near Peterhead) (UKOOA 2002, Q.23, p.67). A dedicated site could be developed and if well maintained it would not pose a significant environmental threat (UKOOA 2002 Qs.23, 68 & 69). However, it is likely that the EU Landfill Directive will reduce the opportunity to dispose of untreated, contaminated cuttings, some of which, if not the majority, will be classified as hazardous waste in future (UKOOA 2002, Task 7, p.25).

B. Processing of solids contained within the contaminated sludge, with an aggregate-like material as the material output, which might be used as a low-grade construction material. This scenario was not thoroughly evaluated in the UKOOA study although the Task 7 report (UKOOA 2002, p.57) does refer to and comment on it. Also it was not made clear whether onshore bioremediation is proposed, in which case the sludge would only contain heavy metals and possibly PCBs (and not hydrocarbons). It should be recognised that if onshore and/or offshore processing became well-established as part of a large-scale decommissioning programme, the processes involved might well become relatively less costly. However, there are no estimates of this in the Case Study A material, so these possibilities could not be considered in detail.

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Viability of all lifting scenarios

Task 7 (UKOOA 2002, 57) investigates the viability of the various combinations of scenarios. It concluded that of the strategies described above, only Strategies IA and IIB (re-injection of slurry and onshore treatment respectively) were considered viable. Strategy IA would be viable for about 25% of the cuttings piles on the UKCS, due to the availability of suitable wells, and would require a change in the restriction under the OSPAR convention on the depositing of waste out to sea. Of the onshore scenarios, both Strategy IIA and IIB seem legal at present. However there are a number of technological gaps and regulatory uncertainties, with further uncertainties about the onshore environmental impacts. 3.5.3 Leaving in-situ scenarios The alternative group of strategies avoids disturbing the cuttings piles and leaves them in-situ. There is potential for some of the toxic aromatic compounds found in older cuttings containing OBM to pass into some benthic organisms found on the seabed (UKOOA 2002, Task 2c). Grant & Briggs (2002) found that the drill cuttings piles around North West Hutton were a source of toxicity to two invertebrate benthic organisms. They further found that the most important cause of the toxicity was hydrocarbons (with polar organics, sulphide, ammonia and other water-soluble substances of much lower significance). However, as noted above, if these entered the food chain, they would very largely be broken down by vertebrates’ detoxification mechanisms (OPG 2002, p.1), so that they should not be passed on through the food chain. Strategy III – Covering cuttings piles – (UKOOA 2002, Task 5b, pp.54 & 55):

Covers can be placed using proven construction methods. They should comprise an initial layer of sand followed by a gravel filter layer and an outer protective layer of armour stone. The issues raised by such a scenario as are follows:

• Development: At present, there is no proven method of construction underneath existing installations although it is likely that methods could be developed.

• Application: Covering is not considered viable for piles around the footings of structures that are fully removed, because, as noted above, the removal process may disperse the cuttings over too wide an area for covering to be feasible. It is however a possible scenario for fully and partly removed steel structures (for example, if the footings were cut off at the level of the cuttings pile) and, possibly, partly removed concrete structures.

• Pile stability: Many piles may be only marginally stable. It is envisaged that there would be a need to ‘build-out’ steep concave pile slopes and to reduce the slopes of steep conical piles by varying the thickness of the initial sand layer. This would ensure pile stability and provide a suitable slope for armour stone of a size which can be placed using existing plant. An alternative approach may be to remove the tops of some piles prior to covering.

• Construction leachate: short-term releases may occur during construction due to cuttings disturbance when placing the initial sand layer. Leachate analyses and ecotoxicology tests using samples recovered from the Ekofisk and Beryl A piles, in combination with

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estimates of potential rates of release during construction, indicate that dilution of the released leachate will be rapid and that the risk of acute or chronic toxic effects will be very low. Limited data from other cuttings piles suggests that this conclusion may apply to a majority of piles.

• Long-term stability: The armour layer will provide adequate short-term protection

against the impacts of severe storms, trawling and collapse of parts of partially removed structures. It is not practical to provide guaranteed long-term protection against the cumulative effects of trawling, emergency anchoring by large vessels and repeated structure collapse events, particularly in the case of part-removed concrete structures.

• Permeability of cover: In the long term, contaminants will be released due to chemical migration and by pore water exchange caused by a pumping action induced by waves. However, the volumes of contaminants associated with this rate of release is expected to be negligible.

• Monitoring and maintenance: both would be required, but the details are not as yet determined.

A risk review (UKOOA 2002, Task 5b, p.12.1), investigating strategic and operational, environmental and health and safety issues, concluded that, as long as the covering succeeded in physically isolating the cuttings for the period during which they pose a threat to the environment, it is generally a low-risk scenario. The integrity of the covering will be determined by the size of disturbances rather than any predictable degradation process. The degree of protection afforded by the covering (and therefore the degree of physical isolation of the covering) were assessed to be: medium for trawling activities; moderate for the eventual collapse of any in situ structure; and low for extremely rare emergency anchoring impacts (UKOOA 2002, Task 5b, p.13.5). Furthermore, the industry believes it can be achieved by developing proven methods of construction and with little or no adverse impact on the marine environment (UKOOA 2002, Task 5b, p.13.5). Strategy IV – Leave cuttings piles in-situ in present form

This strategy, which is permitted under the DTI guidelines and which is not covered by OSPAR, is taken as the reference scenario against which all other scenarios have been compared. The effects of in situ cuttings piles consist of changes in benthic and faunal communities around installations as shown by reductions in indices of diversity (UKOOA 2002, Task 2b, p.25). However, as noted above, the organic components of cuttings piles is thought to be largely be broken down by vertebrates’ detoxification mechanisms, therefore limiting bioaccumulation in fish. More recent work on the current state of drill cuttings piles, and the implications of leaving them in situ, have been carried out in connection with Case Study A, the drill cuttings pile of which is likely to be similar to other large piles in the same part of the North Sea. Historical surveys at Case Study A’s cuttings pile found that a diversity index value considered to be typical of undisturbed communities in this area of the North Sea was reached within:

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• 800-1200m from the centre of the pile in 1992;

• 400m from the centre of the pile in 1997; and

• 300m from the centre of the pile in 2002 after 10 years of natural degradation. The recovery observed was a shift in species from opportunists to those which are characteristic of less disturbed environments (Case Study A, ENV08, p.22). The pile is expected to decrease in size by 40% over a 1,000 year time period, and there is expected to be an approximate 36% degradation in the THC over the same time period. (Case Study A, ENV01, p.10.44). However, this estimate remains very uncertain, as it is sensitive to a number of parameters whose magnitudes are also uncertain (IRG, 2004, p.21). A factor not considered in the modelling of the long-term fate of the cuttings pile at Case Study A was that of the effect of the footings. The relevant report did speculate that, based on expert judgement, local turbulence which may be seen around the footings when left in place may reduce the entombment effect [crust] and cessation of biochemical activity at the pile. This may reduce the predicted physical and chemical persistence of the pile in the long term. Overall, the Independent Research Group (IRG) reviewing and commenting on the studies undertaken for Case Study A in respect of drill cuttings piles left in situ concluded that: “

• The recovery processes will be confined to a thin surface layer and to the periphery of the pile for a very long time, and the areas affected, which are quite small, should realistically be accepted as being environmentally damaged for the foreseeable future.

• There is no reason to regard cuttings piles as a major long-term threat to the environment. They have caused significant damage to small areas of the seabed, which will persist with only slow amelioration if they are not covered or removed.

• Neither the levels of confidence achievable in quantitative predictions of the fate of the seabed environment after decommissioning, nor the extent of difficulties in dealing with cuttings which may be removed to shore, should be overstated.” (IRG 2004, p.9)

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4. ASSUMPTIONS FOR THE FLOW ANALYSIS

4.1 FINANCIAL EXPENDITURE ASSUMPTIONS

The financial expenditures required to recover and process a large steel structure considered in this report are based on early estimates of decommissioning expenditures made for Case Study A. These estimated financial expenditures only cover the costs of reprocessing a large steel structure after well decommissioning and basic clean up (i.e. building on the reference scenario), in line with the scope of the analysis. The extent to which Case Study A may be considered typical of large steel structures is discussed in Section 7. Despite uncertainties it was not possible to present the numbers as a range, as would have been desirable, and the numbers have been cited as given in the source. This should not be taken to imply that they are either certain or precise. Table 4.1 (in which the costs are given in Norwegian kroner) shows that the costs attributed to the removal of the topsides and jackets of Ekofisk (Case Study B) were 50% and 74% respectively of the total removal, transport and demolition costs (highlighted in Table 4.1). The estimated financial expenditures required to remove and deposit the topside and jacket of large steel structures in shallow water are calculated by scaling down total recovery and process costs estimates from Case Study A to these proportions4. Thus, in Table 4.2, the shallow disposal of the topside is assumed to cost 50% (£19m) of the total recovery costs (£37m).

Table 4.1: Proportionate Removal Costs

Topside Jacket

Removal Remove

Component Million kr % Million kr %

Project admin. and engineering

Preparations

Removal 820 50% 1,860 74%

Transport 550 33% 570 23%

Demolition 280 17% 95 4%

Total cost 1,650 100% 2,525 100%

Source: Case Study B, ConocoPhillips 1999

4 It is very likely the cost of removing a smaller platform would not be directly proportional to the cost of a larger platform, and might vary by + or – 10/20%.

36

Table 4.2 Summary of Financial Expenditure Assumptions [£2003, million]

Decommissioning scenarios

Structure type

Structure

Component Leave in situ

(reference scenario)

Shallow disposal

Recovery

Rem

edial action

Bury pipelines

Excavate & leave

cuttings

Cover cuttings

Excavate & cover

cuttings

Re-

inje

ct c

uttin

gs

Rem

ove and treat

cuttings onshore

Topside £191 £37

Jacket £231 £31

Footings £0.22 £30 Large fixed steel

Total £42 £98

Concrete Tank £3103

Pipelines Pipelines £15.2 £1.8 £2.5

Drill Cuttings ~40,000 t

No expenditure

£54 £10.2 £39

Notes: 1 As noted in relation to Table 3.4, the shallow disposal of topsides and jackets is not permitted under the OSPAR Convention 2 Shallow disposal of footings is not further considered here. It is assumed that the footings would be left in situ in a shallow disposal decommissioning scenario. 3 The financial expenditure to reprocess the Ekofisk Tank was estimated to be 3,400 million 1998 Norwegian Kroner respectively (ConocoPhillips 1999, p.137). This was converted into 1998 sterling (@12.50, Norges Bank) and then by use of a UK GDP 1998Q1 – 2003Q1 deflator factor of 114% (ONS) the value of 1998 Kroner can be given in terms of 2003 sterling. This yields an overall conversion factor of 2003£0.0912 per 1998Kr. 4 The financial expenditures for the excavate and leave drill cuttings scenario is based on a ship day rate of £38,000 + the cost of aggregates.

As noted in Section 3.2, leaving the whole structure in situ (the reference scenario) is not a realistic decommissioning scenario (even if it were permitted under the OSPAR regulations, which it is not). Table 4.2 shows that, compared to the reference scenario, the total costs of recovering and recycling a large steel structure are estimated to be £98m. The cost of the shallow disposal of such a structure would be £42m. The potential savings have to be considered with reference to the value of the recoverable material, as well as any wider benefits derived from recycling the structure. The financial expenditure involved in recovering a large concrete tank is estimated to be £310 million at 2003 prices. The financial expenditures involved in removing the pipelines relating to the large steel structure of Case Study A are a little over £15m, for 26 km of pipelines (there is a total of 9,400 km of pipelines in the North Sea area [DTI 1999, Appendix 11). The financial expenditures to manage the drill cuttings under the large steel structure of Case Study A range from zero to leave the cuttings in situ, to £39m to recover, process and landfill the cuttings onshore. This compares to the JIP estimate of £60m (UKOOA 2002, p.23, question 65), based on a per tonne cost estimate of £1,500. The drill cuttings pile investigated in Case Study A was large at 40,000 tonnes and therefore the £39m estimate deriving from this case study would suggest either the use of cheaper removal techniques, or considerable economies of scale.

37

4.2 MATERIAL FLOW ASSUMPTIONS

The flow and endpoints of the materials being decommissioned determine the:

1. Overall cost of the decommissioning process; 2. Input materials required in the decommissioning process and therefore the energy, emissions and the value of this input material; and

3. Material processing requirements, and therefore the corresponding energy, emission and value implications of the onshore processes.

The rates of material recovery are derived from the study of Ekofisk (Case Study B), which was clear in respect of the endpoints of the material (these figures are presented in Tables 4.3, 4.4). This comprises 13 smaller production platforms which do not have fixed footings like the large steel platforms which are the main focus of analysis here. However, the materials in the footings of large steel structures are of similar composition to those found in the jacket. Therefore the rates of material recovery (for each metal type) found for the jackets of Case Study B have been applied to both the jacket and the footings of large steel structures (see Table 4.5). Table 4.3 shows the summary totals from Table 4.4 of the amounts of different materials involved in the decommissioning of the Ekofisk series of platforms, and the rates of recovery (recycling for the metals) which were achieved. There was 100% recovery of steel, aluminium, copper and ballast (aggregates). Overall 85% of both plastics and concrete was also recovered. Of electrical materials (such as electrical articles, instruments, cables and telecom equipment) in the topside, only 10% was recovered. No asbestos or marine growth were recovered. The flows are dominated by the quantity of concrete from the tank, which, at 1 mt, comprised 77% of the total material flow. In total, 92% of the total material flow was recovered, amounting to 1.2 mt of materials. The remaining 107,000 tonnes of material was to be sent to waste disposal facilities; this is here interpreted as going to landfill.

Table 4.3: Summary of Total and Recovered Materials from Decommissioning of

Ekofisk

Total, t Recovered, t Waste, t % Recovery

Topside 103,670 96,463 7,207 93

Jacket 78,620 70,048 8,572 89

Tank 1,049,834 966,134 83,700 92

Pipelines 88,271 80,327 7,944 91

TOTAL (inc. marine growth) of which

Non-metals (excl. marine

growth)

1,320,395 1,069,015

1,212,972 972,292

107,423 20,423

92 91

Source: Table 4.4

38

Table 4.5 then applies these rates of recovery for the different materials to the materials involved in Case Study A, for the two main decommissioning scenarios, Leave in situ and Recovery. In the former case, the material that would have been recovered has to be replaced from other sources, as discussed above, and this is shown in the Replaced column. Table 4.5 shows that 42,500 tonnes, 94%, of the structure of Case Study A is steel, which can be recovered if the structure is returned to shore. In contrast, if the 40,000 tonnes of cuttings are returned to shore, they all need to be landfilled. Table 4.6 gives various estimates, from various sources, of energy and emission factors, and the market values of energy and materials, which have been used in the assessment.

39

Table 4.4: Rates of Recovery from Ekofisk (Case Study B)

Topside Jacket Tank Pipelines

Tota

l t

reco

vere

d t

Waste

t

% R

ecove

ry

Tota

l t

reco

vere

d t

Waste

t

% R

ecove

ry

Tota

l t

reco

vere

d t

Waste

t

% R

ecove

ry

Tota

l t

reco

vere

d t

Waste

t

% R

ecove

ry

Steel 92,000 92,000 0 100% 63,000 63,000 0 100% 46,000 46,000 0 100% 35,000 35,000 0 100%

Aluminium 100 100 0 100% 920 920 0 100% 94 94 0 100% 9 9 0 100%

Copper 2,900 2,900 0 100% 2 2 0 100%

Zinc 25 25 0 100% 40 40 0 100% 590 590 0 100%

Concrete 770 547 223 71% 7,000 5,903 1,097 84% 520,000 440,000 80,000 85% 51,000 44,654 6,346 88%

Ballast 200 200 0 100% 480,000 480,000 0 100%

Electrical 1,300 130 1,170 10%

Plastics 925 786 139 85% 80 72 8 90%

Asbestos 260 0 260 0% 90 0 90 0%

Other 5,415 0 5,415 0% 475 0 475 0% 1,500 0 1,500 0%

Marine growth 7,000 0 7,000 0% 3,700 0 3,700 0%

Total non-metals

(excl. marine

growth) 8,670 1,463 7,207 17% 7,675 6,103 1,572 80% 1,000,000 920,000 80,000 92% 52,670 44,726 7,944 85%

Total 103,670 96,463 7,207 93% 78,620 70,048 8,572 89% 1,049,834 966,134 83,700 92% 88,271 80,327 7,944 91%

Source: Case Study B, ConocoPhillips 1999, various tables.

40

Table 4.5: Proportions of Materials from a Large Steel Structure Assumed

Recovered Note: The table is derived from the material inventory provided by Case Study A, to which the rates of recovery of different materials from the decommissioning of Ekofisk have been applied.

RETURNED TO SHORE AND PROCESSED LEFT IN SITU

Totals % Recovered Recovered Landfilled Left in situ Replaced

t % t t t T

Topside

Steel 20,000 100% 20,000 0 20,000 20,000

Aluminium 20 100% 20 0 20 20

Copper 200 100% 200 0 200 200

Non-metals 300 17% 51 249 300 51

Totals 20,520 99% 20,271 249 20,520 20,271

Jacket

Steel 9,000 100% 9,000 0 9,000 9,000

Aluminium 500 100% 500 0 500 500

Copper 0 0% 0 0 0 0

Marine growth 700 0% 0 700 700 0

Totals 10,200 93% 9,500 700 10,200 9,500

Footings

Steel 10,000 100% 10,000 0 10,000 10,000

Aluminium 300 100% 300 0 300 300

Copper 0 0% 0 0 0 0

Marine growth 1,000 0% 0 1,000 1,000 0

Total 11,300 91% 10,300 1,000 11,300 10,300

Pipelines

Steel 3,500 100% 3,500 0 3,500 3,500

Aluminium 50 100% 50 0 50 50

Copper 1 100% 1 0 1 1

Concrete 1,800 88% 1,576 224 1,800 1,576

Total 5,351 96% 5,127 224 5,351 5,127

Total excl cuttings

Steel 42,500 100% 42,500 0 42,500 42,500

Aluminium 870 100% 870 0 870 870

Copper 201 100% 201 0 201 201

Other 3,800 43% 1,627 2,173 3,800 1,627

Total 47,371 95% 45,198 2,173 47,371 45,198

Cuttings

Cuttings 40,000 0% 0 40,000 40,000 0

Total 40,000 0% 0 40,000 40,000 0

41

Table 4.6: Various Estimates of Energy and Emissions Factors, and Market Values

of Energy and Materials Assumption Energy Value CO2 NOx SO2 Sources

Fuel GJ/t £/t t/t of fuel input

Marine diesel (default) 43.1 £237 3.2 0.0594 0.012 Dti

Road diesel 43.1 £986 3.2 0.0594 0.012 Dti

Heavy oil 40.6 £92 Dti

Aviation fuel 46.1 IP 2000

Iron and steel coal 29.4 IP 2000

Operation per t material GJ/t £ t/t material

Fabricating temporary steelwork 0.22 Energy from electricity IP 2000

Hot cutting 0.05 0.0033 IP 2000

Hydraulic cutting 0.5 0.0368 0.0007 0.0001 IP 2000

Overall dismantling operations 1.15 Energy from electricity IP 2000

Cuttings processing 1.52 3.19

Lorry transport 0.56 3.18 0.04 0.0028 IP 2000

Barge/bulkship transport 0.2 3.2 0.084 0.012 IP 2000

Train transport 0.36 3.17 0.059 0.001 IP 2000

Power GJ fuel/GJ power t/GJ power out

1 GJ of Electricity large industrial consumers 2.46 £8.85 0.0299 0.00024 0.00059

Emissions: NAEI DTI 2003

Manufacture new GJ/t £/t t/t

Standard Steel 25 £300 1.889 0.0035 0.0055 IP 2000

Aluminium 2151

£931 3.5891 0.0041 0.0249 IP 2000

Copper 100 £1,125 7.175 0.02 0.2 IP 2000

Zinc 65 £511 0.024 0.0003 0.0037 IP 2000

Concrete 1 0.156 0.00096 0.00002

Cordah 2000 (UKOOA 2002)

"Plastics" 74 1.479 0.0123 0.0104


Sand 0.05 £4 4.406 0.004 0 UKOOA 2002

Gravel 0.12 £10 10.399 0.009 0 cardigansand.co.uk

Recycling GJ/t £/t t/t

Steel 9 £300 0.96 0.0016 0.0038 IP 2000

Aluminium 151 £932 1.08

1 0.0013 0.017 IP 2000

Copper 25 £1,126 0.3 0 0.12 IP 2000

Zinc 10 £511 0 0 0 IP 2000

Concrete 1 £10 0.156 0.00096 0.00002


"Plastics" 18 1.479 0.0123 0.0104


Landfill GJ/t £/t t/t

Inert landfill gate fee (incl £2/t landfill tax) - NE Scotland £17 Enviros 2000

Active landfill gate fee (incl £15/t post 2004 landfill tax) - NE Scotland £30 Enviros 2000

Hazardous landfill – UK Not known

1 The production of new aluminium from bauxite, compared to aluminium recycling, is an energy-intensive process. The sources used indicate that the CO2 intensity of new aluminium compared to recycled is proportionately much less, but no explanation for this is given

42

4.3 SUMMARY ASSESSMENT OF MATERIAL AND ENERGY FLOWS

For the summary outcome matrices in Section 6, it is necessary to develop a symbolic representation for the relative resource use and rates of material recovery for the different decommissioning scenarios. Table 4.7 sets out a symbolic scheme for the relative energy use and emissions (P), and the rate of materials recovery, for the different decommissioning scenarios (compared to the reference scenario). For relative energy use and emissions, a proportion P greater than 167% of the reference scenario scores - - -, and a P less than 33% scores + + +, with different scores in between as set out in the table. For the rate of materials recovery (RR), this is the proportion of the structure as currently standing which is usefully recovered (i.e. recycled), rather than left in situ or landfilled. A rate of recovery (RR) of more than 85% scores + + +, while one of less than 0.5% scores - - -, with different scores in between as set out in the table. In the summary matrices in Section 6, the RR percentage for the recovery scenarios may be calculated as the (Replaced material)/(Material left in situ) for the reference scenario. The actual percentage is given in the Totals line, under % Recovery, for the scenarios involving material recovery. Table 4.7 Symbolic Scheme for Relative Energy Use and Emissions, and the Rate of Materials Recovery, for the Decommissioning Scenarios

Relative energy use (TER)

and emissions

Assessment of the proportion of energy use and emissions in a scenario (P), compared to the reference scenario where: P ≥ 167% - - - 134% ≤ P ≤ 166% - - 101% ≤P ≤133% - P = 100% = 67% ≤P ≤ 99% + 34% ≤ P ≤ 66% + + P ≤ 33% +++

Rate of recovery of

materials from present

structure

Assessment of the rate of recovery (RR) of materials from the structure as currently standing (i.e. including any marine growth etc.) where: RR ≥ 85% +++ 75% ≤ RR ≤ 85% ++ 51% ≤ RR ≤ 74% + RR = 50% = 25% ≤ RR ≤49% - 0.5% ≤ RR ≤ 24% - - RR ≤0.5% - - -

43

5. NON-FINANCIAL OUTCOMES

As noted above, there are a number of outcomes from the decommissioning process which are not fully captured by the flow of materials and energy, and the corresponding financial flows. Section 5.1 defines and explains the methods used to assess each of these non-financial outcomes in turn, and describes how the outcome will be assessed in relation to the different decommissioning scenarios. Section 5.2 presents a summary of the evidence on the outcomes, which is used in the assessments relative to the reference scenario. The assessments themselves are presented in the text alongside the evidence, and summarised in the summary outcome matrix tables in Section 6.

5.1 METHODS OF ASSESSING THE NON-FINANCIAL OUTCOMES

5.1.1 Clear seabed

There may be value in achieving a clear seabed, which goes beyond the financial implications or the use value of a cleared seabed. The value arises from a desire for a marine environment unmarked by industrial activities. The achievement of this desire is problematic because for many years there have been significant activities in the sea surrounding the UK which have had profound impacts on the marine environment. UKOOA (2001 Part 2B) indicates a direct environmental impact on up to 50% of the surface area annually. These impacts include shipping, marine aggregates extraction, oil and gas extraction, trawling and onshore discharges of chemicals. The impacts include shipwrecks, very extensive alterations to the seabed and its ecosystems, large reductions in fish stocks and the pollution of marine waters. Table 3.8 in Section 3.4.3 showed that there are currently many wrecks and operational submarine cables, as well as oil and gas pipelines, on the seabed. The potential interference of these objects with trawling is discussed in Section 5.1.8. The issue to be assessed here is simply whether or not the seabed has been cleared of materials relating to the operations of the offshore oil and gas industry. However, even if this were to be the case, the seabed would still be very far from being in a condition that was unaffected by human activities. Moreover, if clearing the seabed in this way resulted in a resumption of trawling over the area currently protected by exclusion zones because of the presence of the oil installations, or removed structures that were providing habitats to organisms (such as cold-water coral) then this would certainly leave the affected ecosystems in a less productive and more degraded state than they are in at the moment. There is also no doubt that clearing the seabed of structures, pipelines and drill cuttings would require financial expenditures and give rise to environmental impacts, which are relevant to the desirability of this endpoint, although their relative importance will differ for different stakeholder groups. The assessment of each of the decommissioning scenarios in respect of whether or not it achieves a clear seabed is given in Section 5.2 and reported in the summary outcome matrices in Section 6. It should be clear that a ‘clear seabed’ assessment for a scenario does not necessarily imply that the scenario has delivered net environmental benefits.

44

5.1.2 Health and safety Decommissioning operations require complex and potentially dangerous activities including the handling of extremely heavy structures, much of which is offshore. The oil and gas sector in the UK is experienced in the management of hazards. Much of the work done for the assessment of risks associated with decommissioning oil and gas structures makes quantitative assessments of the probability of a fatal accident (ConocoPhillips 1999) and represents the risk in terms of a sum of the component risks throughout the entire process. Removal decommissioning scenarios involve a large number of relatively low-risk operations, the risk from which is generally considered acceptable.They may also involve two relatively high-risk operations: raising of large structures and divers operating at depth. While doubtless increasing financial expenditures could reduce these risks, they are intrinsically hazardous operations and would remain so however they were undertaken. The standard approach to industrial risk management, as set out for example in reports from the Health and Safety Executive (e.g. HSE 2001) and further explored in relation to the oil and gas sector in UKOOA (1999), is tolerant of the exposure of workers to low-level risks over long periods. Such risks tend to be considered a normal outcome of industrial activity. Far greater efforts are taken to avoid high-level, short-term risks. It is for this reason that the assessment of this issue here has put an emphasis on the two relatively high-risk activities associated with decommissioning scenarios that seek to return structures and associated materials to shore.

5.1.3 Jobs in the UK

Clearly the more expensive scenarios would provide more direct employment. Some of this employment could be in the UK, and, if it were in areas currently affected by unemployment, it could make a significant to economic and social conditions in those areas. However, the assessment of the total net impact on jobs in the UK is complex and a thorough analysis is beyond the scope of this study. The key issues involved are: 1. The degree to which the decommissioning contracts would be captured by UK

companies – A large proportion of the financial expenditure (up to 75%, Watson 2003) is required for offshore equipment. The location of the majority of the structures and the nature of the industry would mean that there would be no particular reason why the decommissioning contracts would be won by UK companies. Furthermore, if the larger parts of the structure were to be returned to shore before being dismantled, there may well not be a deep water ports in Scotland which could

The assessment identifies three possible states of the seabed following decommissioning: 1. Clear of all oil-and-gas related material Clear 2. Any oil-and-gas related material is out of site and inaccessible Covered 3. Oil-and-gas related material is exposed in the marine environment Not clear

The assessment of health and safety provided in the summary outcomes matrix represents an indication of high-risk activities beyond the scope of risks experienced in normal heavy industry. • Raising of large structures - - • Divers cutting at depth - - -

45

receive some of the larger barges used (Case Study A identified Teesside as the nearest UK suitable port). For many of the structures the closest point could well be Norway.

2. The degree to which the material processing would be captured in the UK – Once the structure is returned to shore and crudely dismantled, much of the dismantled parts become a tradable commodity. The scrap steel market is international and is driven by low shipping costs and different steel furnace technologies with differing scrap steel capacities. This could lead to the dismantling and recycling processes taking place in other countries if they could offer lower labour costs and a more favourable scrap market for reprocessing these large steel components.

3. The degree to which any money saved in the decommissioning process (by choosing a

less expensive scenario) would go towards stimulating economic activity and

therefore jobs elsewhere in the economy – This question needs to be largely framed in terms of money expenditure avoided, as the OSPAR convention makes the presumption that the structures will be removed and the industry (and possibly the Treasury) have made financial allocation for these costs. Kemp et al (2001) estimated that overall the UK taxpayer would in effect contribute 50% to the estimated £8.8 billion costs of decommissioning (UKOOA 2002) through foregone tax income. This issue therefore has to be considered in two components:

• The oil and gas industry - to what extent would any additional money be re-invested within the UK, and how job ‘intensive’ would this investment be?

• The UK Treasury - what would be the UK job implications of any additional money? If invested in the public sector services, the money would provide both a high degree of job creation as well as directly providing public services. If the money was to go towards tax cuts, however, the benefit would be less direct but would still go towards stimulating economic activity, much of it in the UK.

An overall assessment of the proportion of employment captured within Norway by the decommissioning of the entire Ekofisk field (ConocoPhillips 1999) estimated that Norway would capture between 36% and 52% of expenditure if all structures were returned to shore and recycled. This has to be compared to the theoretical rate of financial retention and conversion into jobs of any money not spent on decommissioning operations. In broad terms, the UK and Norway are comparable in these terms as they are an approximately equal distance from many of the structures and have a similar-sized oil and gas infrastructure. The analysis quoted above is however an assessment of the goods and services captured and does not represent the more complex assessment of the net impact of employment as discussed above.

5.1.4 Impacts on the marine environment

Marine impacts of structures in situ

As noted earlier, the starting (and reference) point of the analysis for all decommissioning scenarios is after shutdown, well decommissioning, and flooding and cleaning of tanks, process equipment and pipelines, i.e. the structure is clean. The mere presence of such a structure in the sea should therefore not cause significant negative impacts on the biological environment and is considered as negligible in the assessment (its potential to protect or provide a habitat for organisms is considered separately below). The impacts on users of the sea as well as non-use values associated with in situ structures are considered in Sections 5.1.8 and 5.1.1 respectively.

46

The situation is different for drill cuttings piles, as noted in Section 3.5.3. Left uncovered in situ, it is expected that these piles would remain sterile, and potential sources of hydrocarbon emissions into the sea, for many centuries. Covering could allow recolonisation of the piles by marine organisms. Covering would also slow down, possibly to negligible levels, the rate of release of contaminants from the piles. Impacts of marine operations Operations to recover or monitor offshore structures will have some impacts on the marine environment. Some of these may well be very minor, such as the movement of vessels in transit or monitoring vessels. The marine impacts of any monitoring of structures left in situ not requiring remedial activities are likely to be of this kind and are therefore not considered further. Other pollution impacts are assessed according to the schema below. A further impact to consider is the loss of any marine life attached to the structures themselves, which would be lost in the event of removal from the marine environment. A survey of Beryl Alpha and the Brent Spar structures revealed the presence of Lophelia

pertusa cold or deep-water coral colonies at depths of 70-100m (Roberts 2000). A colonisation of this coral is found on the lower jacket of Case Study A. Such corals are characterised by diverse associated fauna. L. pertusa colonies have CITES I (Convention on International Trade in Endangered Species of Wild Flora and Fauna) listing and Annex I status under the EC Habitats Directive. The European Commission’s Habitats Directive (92/43/ECC) requires the oil and gas industry to produce environmental assessments of the impacts of their activities on cold-water corals in the vicinity of their facilities. The UK Government also has an Action Plan for the protection of L. pertusa colonies within UK territorial seas (Case Study A, ENV03). However, Lophelia pertusa is the most abundant cold-water coral species in the north Atlantic and its distribution extends to the Indian Ocean and Mediterranean Sea (Roberts 2000). Colonies on oil and gas structures represent opportunistic colonisations and are unlikely to be considered of conservation importance (Case Study A, ENV01, p.1.1), though they may provide useful opportunities for academic study. Even so, the loss in conservation terms of small colonies of this kind, although not desirable, could not really be considered a significant impact on the biodiversity of the marine environment of the North Sea. Further possible impacts of decommissioning on biodiversity are considered in connection with fish stocks in Section 5.1.9 below. The following scheme will be used to assess the impact of any decommissioning scenario requiring removal or remedial activities:

47

5.1.5 Conservation of stocks of non-renewable resources

A large part of the materials within offshore oil and gas structures are non-renewable; indeed typically 90% by mass is steel. Much of this material could be recycled if returned to shore. Any of this material left in situ (and therefore not recovered) would have to be replaced by the extraction and processing of raw material, in the case of steel this is mostly iron ore and coal. The loss of any non-renewable stock of materials may be important in terms of sustainable development and intergenerational equity. The present market price of materials does reflect some of the scarcity value of non-renewable resources and provides some market signals of the need for their conservation. This perception of scarcity is a perception of present market actors, especially those who have property rights over the material reserves. It is useful to make a distinction between the various different types of resource deposits: 1. The theoretical resource is the sum total of all the deposits of a given resource including deposits not yet discovered. Estimates of these unknown deposits are based on estimates of abundance informed by previous experience of exploration and geological knowledge.

2. Known deposits are all deposits of a given resource which are known about, including reserves.

3. Reserves are economically recoverable resources at present market prices and extraction technology/costs.

As the trading in commodities is predominantly private, the value put on conservation is discounted i.e. there are effectively no price signals provided for scarcity beyond private financial valuation horizons. This is true for a large number of resources where any perceived exhaustion is either hypothetical or not expected for many years. Reserves to production (R/P) ratios provide commodity markets with information on how many years present reserves will last if production continues at its present level and no further reserves are added. Table 5.1 gives estimates for R/P ratios at different dates for different materials from different sources.

• Involves additional minor or short-term impacts or disruption of the marine environment1 -

• Involves continued sterility of seabed occupied by cuttings piles, or localised disruption of ecosystems, larger fish or

marine mammals but not major or long-term physical damage2 - -

• Involves significant impacts on large marine organisms or ecosystems, in extent or duration3 - - -

1 Examples are concentrations of marine vessels under anchorage and working, and impacts from covering or suction dredging cuttings piles 2 Examples include leaving uncovered cuttings piles in situ, and any significant underwater activity or disruption of the seabed or loss of corals on decommissioned structures 3 Examples include extensive disruption of cuttings piles or the use of explosives underwater.

48

Table 5.1: Estimated World R/P Ratios for Various Materials

R/P ratio years

Material 1970 1988 1990 1996 1998 2000 2002

Copper 36 32 36

Aluminium 100 1000 200

Lead 26 12 21

Mercury 13 - 22

Nickel 150 59 52

Tin 17 27 27

Zinc 23 500 20

Oil 42.2 40.9 39.9 40.6

Natural gas 62.1 63.0 60.7 60.7

Coal 224

Sources: Ekins 2000, p.20; Fossil fuel R/P ratios: BP 2003. Note: Much of the variation in the R/P ratios between years could be due to the different sources

It can be seen that some R/P ratios have increased since concerns over the limits to growth in the 1970s (Ekins 2000, p.20), despite increased production and consumption. This is due to exploration and technical progress. However, if a market was to take a pessimistic view of the outcomes of future exploration and technological improvements for a particular resource, then the price of the resource could be expected to increase in accordance with the extent of perceived future scarcity. It may be noted that such a situation is most unlikely to arise in the foreseeable future for iron, which is one of the commonest metals in the Earth’s crust. Of far more potential concern is the availability, price and carbon content of the energy that is required to extract and process it. Clearly countries like the UK which have no appreciable indigenous stocks of some resources, like iron, depend on functioning international markets to gain access to them. When confidence in these markets is low, this may give extra value to resources in use that can be recycled at the end of their lives. However, this situation is both different from resource scarcity itself and, in respect of iron ore at least, is not currently a significant concern. In the analysis of decommissioning scenarios, any stock change in respect of non-renewable resources has to be assessed relative to the reference scenario, both in terms of the resources that could have been recovered had the material been returned to shore (excluding temporary steel which is only relevant to recovery scenarios and which is always recovered itself), and in terms of the resources required to effect this recovery. The loss of non-renewable resources in a scenario may therefore be expressed in terms of a ‘resource stock ratio’ (RSR) of the (useful) material recovered in a scenario, less the mass of fuel required to recover it, to the initial mass of material. Therefore:

RSR = The RSR would therefore be 100% if all the material being considered in a scenario were to be recovered without the need for any fuel use.

Useful material recovered – (mass of input fuel use in recovery) Starting mass of material

49

5.1.6 Impacts of resource extraction

The environmental impact associated with the extraction of material resources varies depending on the material and the method of extraction. An important indicator of environmental impact is the total amount of material which has to be moved to extract a tonne of material.

Table 5.2 Material Multipliers for Resource Extraction and Market Value of

Resource Produced

Extracted resource

End

product

Extraction multiplier

(ratio of mass of materials moved in

extraction to mass of end product)

Market value

(of end product)

t/t £/t

Iron ores Steel 5.2 £300

Copper ores Copper 450 £1,125

Bauxite Aluminium 3 £931

Zinc ore Zinc 32 £510

Crude oil Diesel 1.02 £237

Aggregates Sand & gravel 1.4 Sand: £4 Gravel: £10

Source: Ayres & Ayres 2002, Table A1, p.13 Metal prices: London Metal Exchange 2003, assuming £1 = $1.54

The price of a material will depend on the balance between supply and demand. A relatively scarce material for which there is high demand, resulting in a high market price, will be likely to have a higher extraction multiplier, because companies will have an incentive to extract deeper or otherwise less accessible deposits. A large proportion of the price of the material will then represent the value added in extraction. This is not the case if the value of a high value material is mostly added at other stages of the material value chain, e.g. at the exploration and development stage for oil and the refinery stage for aluminium, when the extraction multiplier is likely to be lower.

Assessment of the resource stock ratio (RSR), the recovered useful material, less the input fuel use, as a percentage of the total material in the structure where: RSR ≥ 67% + + +

66% ≥ RSR ≥ 34% + +

33% ≥ RSR ≥ 1% + RSR = 0% =

-1% ≥ RSR ≥ -33% -

-34% ≥ RSR ≥ -66% - -

-67% ≥ RSR - - - Note: The negative percentages will apply to those scenarios which use a mass of input fuel which is greater than the mass of useful material they recover (e.g. return of drill cuttings to shore for landfilling)

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5.1.7 Impacts of landfill

There are two different types of impacts from an additional amount of waste being landfilled: 1. The direct social and environmental impacts from leaving that particular waste in the landfill site; as well as the

2. Loss of void available to future generations to landfill their wastes. The social and environmental impacts of landfill are summarised in the Table 5.3.

Assessment of the impacts of resource extraction will be through the extraction multiplier (EM), the ratio of the mass of the total material moved to the mass of the end product extracted: EM ≥ 1.67 - - -

1.66 ≥ EM ≥ 1.34 - -

1.33 ≥ EM ≥ 1.01 - EM = 1.0 =

0.99 ≥ EM ≥ 0.67 +

0.66 ≥ EM ≥ 34 + +

0.34 ≥ EM + + +

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Table 5.3: Impacts of Landfill Sites

Receptor Activity Potential Impact

Surface water hydrology and channel morphology

Use of vehicles and machinery, and site drainage

Increase in surface run-off from ground compaction with rapid transfer of rainwater to watercourses via drains. Changes to flow regimes due to site drainage may cause deposition downstream, with increases to sediment loading, potentially increasing soil erosion and flood risk.

Surface water quality

Leachate and materials management

Potential decrease in water quality from sudden releases, for example a failure in the landfill liner; or from gradual leachate seepage.

Groundwater hydrology

Physical presence of landfill Continued alteration of groundwater flow.

Groundwater quality

Leachate and materials management

Contamination due to sudden releases, from leachate seepage to groundwaters, and from spills or leaks of fuel and oil.

Soils Waste disposal, and use of vehicles and machinery

Contamination of soil from toxic or hazardous materials being disposed of. Soil compaction, erosion and contamination from vehicle movements and road run-off.

Geology Excavations Removal of geology following expansion of the site.

Local air quality

Regional / global air quality

Landfill gas generation

Releases of methane (landfill gas) to the atmosphere, contributing to the greenhouse effect. Risk of explosion should the methane be contained within a confined space, therefore flaring is required. Odours from the landfill gas emissions.

Aquatic ecology Waste disposal and materials management

Risk of pollution to adjacent watercourses by leachate.

Terrestrial ecology Physical presence of landfill, landfill gas generation and waste disposal activities

Alteration of site leading to loss of habitats. Operation of the site will lead to the attraction of vermin (a nuisance issue). There may be harm to local species through the release of the landfill gas, and through disturbance due to traffic movements.

Health and Safety Waste disposal operations and the generation of landfill gas

Risk of harm to humans from handling toxic and hazardous materials, and through consumption of contaminated groundwater.

Nuisance Use of vehicles and machinery, and site management

Increased HGV traffic resulting in increased emissions, dust, noise, and mud on roads leading to the landfill site. There will be odours from the waste disposed and from the landfill gas emissions. Production of unsightly litter, attracting vermin.

Source: Case Study A, E01, p.10.8

The key environmental impacts are leaching, landfill gas and the impact of lorries. These impacts are discussed in more detail below (taken from Case Study A, E01, p.10.9):

• Leachate is generated when rainwater percolates through the landfill, makes contact with the buried wastes and extracts the soluble components. Depending on the characteristics of the landfill and the wastes it contains, the leachate may be relatively harmless or extremely toxic. Generally, leachate has a high biochemical oxygen demand (BOD) with high concentrations of organic carbon, nitrogen, chloride, iron, manganese, and phenols. Many other chemicals may be present, including pesticides, solvents, and heavy metals. The nature of leachate is such that it can permeate into adjacent water bodies and penetrate groundwater, and its effects can be detected downstream and even across country boundaries.

• Landfill gas (LFG) is composed of carbon dioxide and methane, both of which are colourless and odourless. It is an important and relatively long-lived greenhouse gas, having a global warming potential 31 times greater than carbon dioxide over a 100

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year time horizon. Decomposition of biodegradable wastes within landfill sites is one of the major contributors to emissions to the atmosphere, contributing approximately 30% of anthropogenic methane emissions in the EU. However, the process of capture of this LFG and its use as a source of fuel in power generation is an established practice in many of the larger landfill sites in the UK. Furthermore, as the power generated from LFG is eligible for Renewable Obligation Certificates (ROCs), LFG is increasingly seen as an asset and the extent of LFG capture is set to increase. If not captured, and if confined in spaces, LFG poses a significant risk of explosion or asphyxiation. Landfill gas contains over 150 trace components which can cause other local or global environmental effects such as odour nuisances, stratospheric ozone layer depletion, and ground-level ozone creation.

• There could well be increased movement of lorries during the onshore dismantling and disposal process. There may by opportunities for the transport of bulk material by barge (Case Study A, E01, p.9.10), although this would require a suitable water link from dismantling site to landfill site. Any impact would be most marked with large bulk structures such as concrete structures and large steel structures, and would occur whether the material was reprocessed or not. If lorries were used, there would be increased noise, pollution, disruption to traffic as well as heightened risk of accidents to road users. Generally these impacts are tolerable in that they occur routinely, although the use of small or rural roads may heighten the exposure in an inequitable way to local residents. The net impact of lorries related to the recovery of oil and gas structures is difficult to assess. If it is assumed that the impacts (such as road deterioration and air emissions), and the exposure of people to them, caused by lorry movements for the recovered material are the same as would be caused by the movement of lorries for the movement of virgin material, then the additional impact from lorry movements related to bringing a structure to shore would arise only from the material that needs to be landfilled.

The loss of void space The number of sites which are suitable and socially acceptable for the establishment of landfill sites is increasingly limited. The loss of void space suitable for landfill can be described as a loss of option value to future generations and therefore has value to the present generation in terms of a bequest of a resource to future generations; the additional loss of void is therefore a matter of intergenerational equity. This value is in some ways equivalent to that of the loss of non-renewable resource as described in Section 5.1.5, as the loss of void space to landfilling is in practice non-reversible. The future scarcity of landfill void would potentially be communicated through market signals and therefore the gate fee charged by the owner of the landfill site. However, due to the timescales involved and individual discounting of future values, much of this signal fails to be reflected in the gate fee. The landfill tax is in part an attempt to try to reflect this value and the environmental impacts of landfill. In 2004-05 the landfill tax will be set at £2 and £15 for inert and biodegradable waste respectively, with the latter due to rise by £3 per year until it reaches £35 per tonne (as the vast majority of decommissioning of offshore structures will occur after 2004-05, this increased tax will increase the costs of onshore disposal for those decommissioning scenarios that generate non-inert materials for landfilling). In this study, the non-financial outcome of landfilling (that value not captured by the gate fee and landfill tax) is taken to be influenced by three factors: 1. The amount of waste to be landfilled; 2. Whether the waste arising is biodegradable or inert;

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3. Whether some part of the waste is classed as hazardous The Landfill Impact Factor in the box below takes into account in an additive way the loss to society of void space and of landfilled materials (MT), and the environmental impacts of biodegradable and hazardous wastes (MB, MH). It may be noted that this equation implies that tonne for tonne, the loss of void and resources, biodegradability and whether the waste stream is hazardous are weighted equally. This is obviously a fairly crude assumption about the relative social disbenefits arising from these different impacts of landfill. In particular, it may seem a relatively low weighting for hazardous waste. The weighting may be justified by the fact that hazardous wastes are increasingly well managed in dedicated landfill sites and therefore much of the environmental threat is dealt with and reflected in the higher gate fees (the gate fees may also be expected to reflect the shortage or hazardous waste sites following the recent European prohibition of co-disposing of hazardous wastes with other wastes). It would be possible to change this assumption in sensitivity analysis if it seemed likely that landfill impacts of a particular kind were of importance in a particular decommissioning scenario.

5.1.8 Impacts on the fishing industry

The fishing industry is an important stakeholder in what happens in the North Sea. However, it should be noted that the fishing industry in the North Sea is not homogeneous, and the different outcomes from decommissioning would affect different parts of the industry in different ways. Thus, trawlers might be expected to favour a clear seabed approach to decommissioning, to enable them to trawl without obstructions, whereas net setters might favour residual structures if they perceive them to aggregate fish (as, for example, with wrecks). However, in the Scottish sector of the UK Continental Shelf, there is a clear consensus in favour of a clear seabed post-decommissioning5, and it is in relation to this that impacts of the various decommissioning scenarios have been evaluated. Historically, the fishing industry was entitled to fish in the areas where there are now exclusion zones around oil and gas structures. The outcome from the different decommissioning scenarios could impact on their business in the following ways:

I. If there are removal or remedial activities:

5 Personal communication, Michael Sutherland, Scottish Fishermen’s Federation, August 2004

Landfill impact factor (LIF) = Σ [MT + MB + MH] Where:

MT = Total mass of waste being landfilled in tonnes

MB = Mass of biodegradable waste being landfilled

MH = Mass of hazardous waste being landfilled

The assessment according to the landfill impact factor is as follows: 100 < LIF < 1000 -

1000 ≤ LIF <5000 - -

LIF ≥ 5000 - - -

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• This could involve short-term restrictions on the movement of all non-operational vessels in the operational area, typically lasting for a few weeks or months, and would only be an additional restriction to fishing in the case of pipeline operations, as there is an existing exclusion zone of 500 metres around all platforms during their operational phase.

• The removal processes would involve some short-term impacts on the local marine environment. The most significant of these would be the use of explosives to remove the footings if other removal methods proved to be unfeasible. This may cause some disruption to the seabed, to drill cuttings piles (and resulting contamination by the pollutants contained in them) if they had not already been removed, and disturbance to fish and marine mammals (although it may also be noted that quite effective techniques to mitigate against the shock waves from explosives have been developed).

• During the suction dredging of drill cuttings, there would be little pollution of the water column other than the plume caused by the remotely operated vehicle (ROV) whilst in contact with the cuttings pile. Using present technologies (the Breebot crown cutter), if there was a blockage in the suction hose, it would have to be cleared by back washing. This would lead to re-suspension back into the water column of a proportion of the cuttings material which was present in the hose when the hose was blocked. Little secondary pollution would be discernible at a distance of 100 metres from the dredging operations, and no effects would be seen on the sea surface. (UKOOA 2002, 20, Q48)

II. If any structure or cuttings pile is left in situ:

• This would involve a certain impact on long-term trawler fishing activities in that fishing vessels would need to avoid any in situ materials. It could be hazardous for the trawler vessel in the case of footings, and potentially hazardous for the marine environment in the case of cuttings piles for trawling activities to reoccur at the site after decommissioning had finished: a. The present exclusion (or safety) zones of 500 metres are automatically created around above-surface installations under section 21 of Petroleum Act 1987 and will remain after decommissioning provided the structure still protrudes above the surface. The Health and Safely Executive (HSE) could take statutory action to cancel a zone and would probably not do so unless someone requested it, e.g. fishermen6.

b. The footings of large steel structures left in situ would not automatically have an exclusion zone as the existing zone would cease to exist as soon as a structure no longer breaks the surface, so:

i. The DTI could make regulations under the Petroleum Act 1998 enabling it to create zones for any structure on the seabed. However, the DTI currently feel this is unlikely to be justified given the current advice from fishery and transport experts that marking on charts etc. would be sufficient for the prudent mariner to avoid the obstacle7.

ii. There is a provision under Part 1 of the Food and Environmental Protection Act 1985 for fishing exclusion zones to be created; this could be used by the Food Standards Agency if there was concern about the quality of fish caught when trawling through an old drill cuttings pile left in situ after the removal of a platform. However, there

6 Personal communication, DTI oil and gas department, Keith Mayo, January 2004. 7 Personal communication, DTI oil and gas department, Keith Mayo, January 2004.

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is no evidence to suggest that demersal fish frequenting historic cuttings piles have more hydrocarbon contamination than fish found elsewhere, and there is no evidence that the nature of hydrocarbon contamination in fish from cuttings piles is different from that of open sea fish (Case Study A, E1, page 10.23). As noted in Section 3.5, there is potential for some of the toxic aromatic compounds found in older cuttings containing OBM to pass into some benthic organisms found on the seabed (UKOOA 2003, Task 2C), but there is certainly no evidence of these having been passed on through the food chain to fish.

c. If all 44 fixed structures [33 large steel + 11 concrete (DTI 2002, Annex 2A, p.44)] eligible for derogation were to have a 500 metre exclusion zone after decommissioning, the total loss of fishing grounds would be 33 km2, or 0.01% of the UK North Sea assuming that there is no overlap (updated from AURIS 1995, p. 6.3). Fishing activities would most likely continue around decommissioned pipelines left in situ and therefore the risk to the fishing fleet needs to be assessed. Table 5.4 reproduces information from Tables 3.7 and 3.8 which is relevant to risks to trawling from pipelines and other objects on the seabed.

Table 5.4: Estimated Total Number of Interactions1 Between Fishing Gear and

Objects in the North Sea

Feature Potential interactions per year

Operational submarine cables 26,000 Wrecks 48,000 (likely to be more)

Pipelines 36,000

Level of pipeline deterioration Year 10 Year 30 Year 50

Any part of pipeline 36,000 36,000 36,000

Exposed sections 15,000 14,000 13,000

Spanning sections 500 1,200 1,300

Section with a break1 20 50 140

Source: AURIS 1995, p.6.28 1 ‘Interaction’ in this context includes passage over buried as well as unburied pipelines. 2 As the pipelines age, decay and rust, breakages in the pipelines could occur, potentially leaving jagged edges.

It is important to note that by no means do all interactions between fishing gear and marine features result in any noticeable impact. This is because:

• The results in Table 5.4, derived from modelling, assume random fishing over the pipeline network as it currently exists. However, pipelines posing more of a hazard of spanning and breaking are more likely to undergo remedial action or removal.

• Any decommissioned pipelines left in situ would be charted and the use of FISHSAFE will ensure proximity alarms are available to the Scottish fleet. In the Southern North Sea, sand waves can cause the creation and movement of sections of pipeline not in contact the seabed (spans). To reduce the chances of trawlers interacting with spans, any pipeline left in the Southern North Sea could have ongoing monitoring and updates on FISHSAFE on the whereabouts of any spans.

• There will be some self-burial of pipelines in the Northern North Sea not already buried. One estimate suggested that eventually 70% of the diameter

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would be buried. (AURIS 1995, page 6.25). This would be different in the Southern North Sea;

• Only very large diameter pipelines, broken pipeline sections or spanned sections which are broken during the interaction could plausibly lead to a snagging incident and therefore pose a safety hazard;

• Snagging is most likely to result from particular gear in particular circumstances8.

These interactions should also be considered in context with other snagging hazards managed by trawler skippers, most noticeably wrecks, the modelled frequency of which is shown in Table 3.5. A recent survey (Case Study A, S1 page 4-5) of fishing vessel skippers’ perceptions of the impact of decommissioning on their activities found that:

• The preference expressed by the trawling skippers was for the complete return of the seabed to its original form.

• Large objects like legs remaining would be considered as the ‘worst situation feared by skippers’.

• Concern was centred both on the risk of the loss of fishing gear as well as the risk to the vessel and the crew.

• There were mixed concerns on pipelines ranging from acceptance if they are buried and regularly surveyed, to concern over safety and pollution if they are broken during fishing activities.

• The concerns around drill cuttings were largely centred on the possibility of the banning of fishing.

As noted above, the impacts discussed in this section do not impact on all fishing activities. Anglers, trappers, and long-line and net fishermen will not be affected in the same way by any structure left on the seabed at such depths (typically 100 metres or more). In fact, the protection of spawning grounds and local fish stock from trawling activities would have a benefit for the activities of these fishermen (see next section). For this assessment, two impacts on the trawler fishing industry seem important to include: the risk of snagging and the desire of fishermen for the return of current exclusion zones to fishing use. The assessment scheme for these impacts is given below.

8 Specifically: ‘Snagging may occur where an Otter door (improperly oriented in a flat position) slips under a span of insufficient height to allow a quick release. The result would most likely be a minor displacement of the line, which might occur with non-adapted beam trawls using a single bridle attachment to the shoe’ (AURIS 1995, p.6.27).

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5.1.9 Impacts on fish stocks (and other marine life)

The steel jackets of oil and gas platforms in the North Sea already act as artificial reefs; the densities of fish in and immediately around jackets is higher than that of the “open” sea away from the jackets (Case Study A, page 10.22). If the footings [of large steel structures] were left in situ it is very likely that the same effects would occur; the remaining structure would act as an artificial reef. While the focus of this section is on fish, the comments below would also apply to some extent to other marine organisms that are attracted the structures and that take advantage of the protection from fishing and environmental disturbance from fishing that these structures. In other words, the reef-effects can be beneficial to marine biodiversity in general, and not just fish. The footings of large steel structures found in the UKCS would typically extend to 30 or more metres above the seabed and provide the type of open lattice-work structure that is attractive to shoaling and bottom dwelling fish. Higher densities of fish would be found within and around the footings than would be found in the open sea nearby. The density of fish would fall very quickly at distances of more than about 20m beyond the footings. The potential benefits of the creation of the reef focus largely on the effect that the reef will have on attracting fish to the site and providing them with an environment that:

• increases the carrying capacity of the local sea area, so allowing a higher density of fish to live in that part of the sea;

• permits the healthy growth of adults and juveniles;

• protects the fish from the pressures of trawler fishing activities; and

• protects areas of seabed from the impacts of mobile fishing gear – trawling activities can plough furrows up to 2m wide and 0.3m deep, inflicting great disturbance on the sediment and the benthic communities inhabiting the seabed (Dayton et al. 2002, p.26).

The greatest benefit in the long term will be derived by the aggregation of fish at the site, and the eventual dispersal to the "open sea" of fish which have spent some time at the reef (Kjeilen et al., 1995 p.53). Research suggests that there is some relationship between the number of shoaling fish found at a platform and the volume of water “enclosed” by the structure. An average figure of about 0.3kg wet weight of fish per cubic metre of enclosed space has been estimated for platforms in the Central and North Sea in the UKCS (Case Study A, E1, p.10.23).

• The risk of snagging: o For the inconvenience of loss of gear (with the potential to be compensated by the industry) -

o For the risk to crew -

• The return of fishing grounds after the removal (or making safe) of the structure or cuttings pile (relative to the reference scenario) +

Note: It may appear that the above assessment is putting equal weighting on the incidence of loss of fishing gear and loss of life. This is not the case as by no means would all incidents of loss of fishing gear through a snagging incident lead to the loss of life. Risks are calculated by the multiplication of the consequence of a particular risk event occurring by the probability of that consequence actually occurring. The probability of the loss of life from a snagging incident is very low compared to the probability of loss of fishing gear.

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• Footings: with a base area of about 4 hectares (Case Study A, E1, p.10.23) and a height of 30-50m the volume enclosed by the footings of large steel structures could be some 120,000-200,000m3. If the average mass of fish were 0.3kg/m3, the mass of fish that may be found in and around the footings at any one time could be 36-60 tonnes. This is likely to be an over-estimate because the density of fish generally decreases towards the base of steel platforms. If the footings were collapsed inwards on top of the cuttings, the reef effect would be less marked. The enclosed space offered by the mound of steel material would be less than that offered by the intact footings. It is therefore likely that fewer fish would be found, and the species present would be dominated by bottom dwellers such as ling and wolf fish that spend most of their time resting on the seabed or on hard surfaces.

• Jacket: If a jacket of a typical large steel structure was cut at 40 metre sections and left as a reef, there would a total reef footprint of about 9 hectares. With an enclosed volume of 350,000m3 (based on calculations from the dimensions of Case Study A, E1, p.6.7), the mass of fish found in and around the created reef at any one time would be approximately 100 tonnes. The edge of reef factor would be reduced relative to the footings as the reef created by one piece of cut-up jacket put close to another would have a lower perimeter to area ratio.

• Topside: The topside from a large steel structure would have a reef volume of approximately 150,000m3 and would contain fish of mass 45 tonnes at any one time.

If these estimates were extended for all 33 of the large steel fixed structures presently on the UKCS, the total ‘reef’ effect on fish stocks at any one time would be approximately 6,400 tonnes. It should be noted that such an enclosed space could act as a spawning or nursery area for many generations of fish, which may then disperse to the open sea. Therefore, the benefits to total fish stocks in the North Sea and therefore long-term catches will be greater than this estimated mass of fish resident in the enclosed space at any one time. No reliable estimate of the relationship between resident spawning stock and impact on catch, or of the distribution of species, which will have different commercial values, is available, but it may be surmised that any benefit to fish stocks could become of some benefit to the fishing industry when fish leave the immediate protection of the structure. As noted above, there is no evidence to suggest that demersal fish frequenting historic cuttings piles have more hydrocarbon contamination than fish found elsewhere, and there is no evidence that the nature of hydrocarbon contamination in fish from cuttings piles is different from that of open sea fish (Case Study A, E1, p.10.23).

The benefits to fish stocks from the decommissioning scenarios which leave various materials in situ have been assessed as follows: Non-trawler area with little enclosed space + In-situ footings or shallow deposit of topside + + Jacket left in the marine environment + + +

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5.1.10 Summary of the assessments of non-financial outcomes

Table 5.5 summarises the various symbols which give the assessments of the material and energy flows, and other non-financial outcomes, which have been explained above. These symbols appear in the summary outcome matrices of Section 6. First, however, the evidence on which the assessments are based needs to be presented. This is the subject of the next section.

Table 5.5: Summary of Proposed Assessments of Non-Financial Outcomes

Non-financial outcome Proposed assessment Assessment score

Relative energy use (TER)

and emissions

Proportion of energy use and emissions in a scenario (P), compared to the reference scenario where: P ≥ 167% - - - 134% ≤ P ≤ 166% - - 101% ≤P ≤133% - P = 100% = 67% ≤P ≤ 99% + 34% ≤ P ≤ 66% + + P ≤ 33% +++

Rate of recovery of

materials from present

structure

Rate of recovery (RR) of materials from the structure as currently standing where: RR ≥ 85% +++ 75% ≤ RR ≤ 85% ++ 51% ≤ RR ≤ 74% + RR = 50% = 25% ≤ RR ≤49% - 0.5% ≤ RR ≤ 24% - - RR ≤0.5% - - -

A clear seabed

Seabed clear of all oil-and-gas related material Clear Any oil-and-gas related material is out of site and inaccessible Covered Oil-and-gas related material is exposed in the marine environment Not clear

Health and safety Raising of large structures - - Divers cutting at depth - - -

Jobs in the UK No assessment in the summary outcomes matrices

Impacts on the marine

environment

Additional minor or short-term impacts - Localised disruption of ecosystems or components of them - - Significant impacts on ecosystems or components of them - - -

Conservation of stocks of

non-renewable resources

Where RSR is relative loss of non-renewable resources: RSR ≥ 67% + + +

66% ≥ RSR ≥ 34% + +

33% ≥ RSR ≥ 1% + RSR = 0% =

-1% ≥ RSR ≥ -33% -

-34% ≥ RSR ≥ -66% - -

-67% ≥ RSR - - -

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Impacts of resource

extraction

Impacts of resource extraction; extraction multiplier (EM) is the ratio of the mass of the total material moved to the mass of the end product extracted: EM ≥ 1.67 - - -

1.66 ≥ EM ≥ 1.34 - -

1.33 ≥ EM ≥ 1.01 - EM = 1.0 =

0.99 ≥ EM ≥ 0.67 +

0.66 ≥ EM ≥ 34 + +

0.34 ≥ EM + + +

Impact of landfill

Where Landfill impact factor (LIF) = Σ [MT + MB + MH]: 100 < LIF < 1000 -

1000 ≤ LIF <5000 - -

LIF ≥ 5000 - - -

Impacts on the fishing

industry

Risk of loss of gear - Risk to crew - Return of fishing grounds +

Impacts on fish stocks

(and other marine life).

Non-trawler area with little enclosed space + In-situ footings or shallow deposit of topside + + Jacket left in the marine environment + + +

Note: It must be stressed that in any overall assessment of the scenarios, there can be no addition of the +

and - signs across the different issues, because they are incommensurate

5.2 EVIDENCE FOR THE ASSESSMENTS

Tables 5.6 and 5.7 give the evidence on the decommissioning of large steel structures that has come from Case Study A, as it relates for different decommissioning scenarios to three of the non-financial outcomes discussed above: the endpoint of the seabed (clear, covered or not clear); the impact on the marine environment; and the amount of material recovered and landfilled. The content of the three tables will be briefly described and summarised in turn. The letters used for the decommissioning scenarios are taken from Table 3.4. As discussed above (Section 3.2) the reference scenario (T1, J1, F1, CON1, P1, C1) against which the other scenarios are to be compared entails leaving all the materials (structure, pipelines and drill cuttings) in situ, after basic cleaning of the topside. T1 and J1 are currently against the OSPAR convention and therefore are not being contemplated in practice. Were this situation to change, and these to become practicable scenarios, the topsides and jackets left in situ would need regular maintenance and monitoring to ensure that they did not pose any risk to other users of the sea or the environment. The cost of a vessel to undertake such monitoring is approximately £38,000 per day (Case Study A, Soc 05, p.11). However, T1 and J1 are not further considered here as no stakeholders appear to consider them practicable options in the North Sea context and their implications have therefore not been studied in any detail. F1 (with the topside and jacket having been removed to the regulated extent), although requiring derogation under OSPAR, clearly is a practicable option, as are CON1, P1 and C1. They are therefore considered in some detail below. In all these cases monitoring of any materials left in situ would be required, at the kind of daily cost cited above, and some indication of what this is likely to entail is discussed now. For pipelines left on the seabed (P1) it has been estimated that they should be surveyed once every ten years over 100 years (Case Study A, Eco 05, p.11). With about 9,400 km of

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pipelines in the UKCS North Sea (DTI 1999, Appendix 11), if a substantial proportion were left in situ, this could employ a survey vessel for approximately 25% of its offshore time9. The environmental implications of drill cuttings left in situ (C1) have been discussed in some detail in Section 3.5. The UKOOA study (UKOOA 2002, p.15) considered that a monitoring program should be based on the protocol used for seabed monitoring at producing field sites, but should also include sampling and analysis of the pile itself. A minimum of two monitoring surveys should be undertaken at an interval of 3 years. The outcome of these surveys should then be used as basis for considering the need for any further survey. For Case Study A (ENV 02, p.39, UKOOA 2002, Final report, p.15), the energy calculations allow 30 days (3-day survey every five years for 50 years) and therefore 150 tonnes of diesel, for monitoring in situ cuttings piles. The energy use from monitoring activities (for all the non-reference in-situ scenarios involving structural elements, pipelines or drill cuttings) does not appear in the summary matrices of decommissioning outcomes in Section 6, because the monitoring requirements for these scenarios have not been sufficiently defined in the source documentation. Such energy use should, however, be taken into account in any conclusions about the scenarios. Sometimes, as a result of monitoring, a need for remedial action is respect of materials left in situ will be revealed. The financial implications of such remedial action have not been included in the assessment, but should be considered in connection with the ongoing liability of the industry for materials left in situ.

5.2.1 Clear seabed

The reference scenario entails leaving the topside (T1) in situ after shutdown, well decommissioning and the flushing and cleaning of tanks and process equipment. The jacket (J1) and footings (F1) would be left in situ. If the footings were to be left on their own, they would be cut from the jacket at the highest point of the piles. The pipelines would be cleaned to minimise the oil content, and might either be flooded with sea water or filled with inert fluid, containing less than 40ppm oil, sealed and left in place (P1). The drill cuttings piles would remain undisturbed (C1). This scenario, in part or whole, obviously does not leave a clear seabed. In the shallow disposal scenario the topside (T2) would be deposited on the seabed at the present location, and the jacket ( J2) would be cut into 8-10 sections and deposited on the seabed around the present location. The footings would not be cut unless they were to be removed to shore, either without the cuttings (F2a, in some cases for the cuttings the outcome would be similar to C2, as up to 100% of the cuttings could be dispersed into the water during the removal of the footings) or with them (F2b, C4). The shallow disposal of any part of the structure also does not leave a clear seabed. For removal of the structure to shore, the topside (T3) would be removed in 22 modules, and reprocessed onshore, with some of the more hazardous material (e.g. asbestos) removed. The jacket (J3) would be removed in 8 to 10 sections and reprocessed. The footings (F2a,b) would be either cut at the level of the cuttings or detached from the seabed (perhaps requiring the use of explosives), cut up and transported to shore, with or without the cuttings. This would effectively leave a clear seabed as far as the structure was concerned.

9 Calculation based on assuming that a survey vessel can survey 13km of pipeline per day (Case Study A, Eco 05, p.11), and is offshore for 80% of its time.

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For the pipelines a clear seabed would only be achieved by their removal to shore (P2). Other scenarios are leaving them in situ with remedial action (P3, cutting or covering unstable or spanning sections), or burying and leaving them. For the cuttings, again only their removal to shore (C4) would leave a clear seabed. Other scenarios are covering the undisturbed pile with layers of inert material such as sand, gravel and rock (C3), or ‘excavating’ the pile (C2), which entails using a propeller to direct a low velocity, high volume flow of water vertically downwards onto the pile, which would scatter it in a thin layer over several hectares, leaving the material to biodegrade over several years. Only two scenarios for a concrete structure are considered: left in situ (CON1) and removed to shore (CON2). Only the latter would leave a clear seabed.

5.2.2 Marine environmental impacts

Table 5.6 describes and assesses (in accordance with the method described above, Section 5.1.4) the impacts on the marine environment of the different scenarios. The table contains a great deal of very detailed information, mainly from the Case Study A. The outcomes may be summarised as follows. The impacts of the reference scenario are described in the first column. In the normal course of events, and with the exception of the drill cuttings piles, the impacts of leaving all this material offshore will be small, although the eventual collapse of the topside and jacket might disturb the cuttings piles in due course. The cuttings piles would render the relevant area of the seabed sterile for many centuries, but would very gradually biodegrade, and some material would leach out into the environment. The overall impact of this is assessed as medium (‘- -‘). All the other decommissioning scenarios (for the structure and pipelines) cause a greater impact on the marine environment than the reference scenarios, because:

• The shallow disposal of the topside (T2) and jacket (J2) would disturb the cuttings pile. Their removal would give rise to localised disturbances to the environment and the loss of corals on the decommissioned structures.

• The removal of the footings with the cuttings in situ (F2a) could scatter up to 100% of the cuttings over a wide area, with an impact assessed as ‘- - -‘. The impacts would be less, and the same as for the jacket (‘- -‘), if the cuttings were removed with the footings (F2b) (this assessment might also apply to the ‘hybrid’ options described in Section 3.1.6, just removing those cuttings around the footings, or cutting the footings at the level of the cuttings, but it was not possible to assess these options in detail). If explosives were used to sever the piles from the seabed, there could be damage to marine organisms (although there are techniques to mitigate this). This would make the impact assessment for these scenarios more negative.

• For the pipelines all the non-reference scenarios involve some damage to the marine environment, but it is localised and not long term (‘- -‘).

For the drill cuttings, covering them (C3) would encourage the re-establishment of a healthy seabed community, with only short-term environmental disturbance, and is therefore assessed as ‘-‘, or positive (‘+’) compared to the reference scenario. Removing the cuttings (C4) with a suction dredge would also only cause short-term impacts, and is also assessed as ‘-‘, or positive (‘+’) compared to the reference scenario. The excavation scenario (C2) involves significant environmental damage, possibly resulting in a surface oil slick, with an impact on

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seabirds and sea mammals, and the smothering of benthic organisms over a wide area. To reflect this, C2 is assessed as ‘- - -‘, or ‘- (- -)’ compared to the reference scenario.

5.2.3 Landfill impacts

Table 5.7 gives the evidence for the assessment of landfill impacts, with the assessment carried out according to the method described in Section 5.1.7. The total landfill impact of removing the structure and pipelines to shore is relatively small, with 2,173 tonnes of material landfilled in all, with a total Landfill Impact Factor (LIF) of 3,439. For drill cuttings it is a very different story. The nearly 40,000 tonnes of cuttings has an LIF of more than 115,000, considerably more than that which the 80,000 tonnes of concrete would have if it were to be brought ashore.

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Table 5.6: Evidence for the Assessment of Marine Impacts Note: In the table the A references, followed by another letter/number refer to documentation from Case Study A. B references refer to Case Study B.

Description and assessment of environmental marine impacts

Structure type

Structure Component

Reference scenario

(T1, J1 & F 1, CON 1, P1 & C1)

Shallow disposal

(T2 & J2)

Assessment

Assessment relative to

reference scenario

Removal and reprocess (T3 & J3)

(Also used in shallow disposal)

Assessment


reference scenario

Topside

- -

A, E01, 12.3: There would be no planned discharges of oil or

chemicals to sea other than those from the normal operations of

vessels.

- -

Jacket

A, E01, 10.5: Disturbance of the pile [resulting from the depositing of the topside and jacket] would result in the re-suspension of contaminants into the water column and onto the surrounding seabed. A, E01, 10.3: The effects on the water column would be localised and temporary because contaminants would be rapidly dispersed and

diluted. - -

- -

A, E01, 12.3:

Most impacts would be very

localised and short-lived, and similar to those that arise during the normal offshore activities.

A, E01, 12.3: The jacket legs and members do not contain any oil or chemicals, and the bulk of material that would be handled is steel and sacrificial anodes made of aluminium alloy.

- -

- -

Removal with cuttings in situ (F2a) Removal with cuttings also removed (F2b)

A, E01, 12.3, A, Tec 10, p.6:: A proportion [in a worst case scenario up to 100%] of the drill cuttings pile

would be re-suspended. The effects on the water column would be localised and temporary because contaminants would be rapidly dispersed and

diluted, but the cuttings could re-settle over a wide area

- - -

- - - As with the removal of the topside and jacket,

there would be no planned discharges of oil or chemicals to sea other than those from the normal

operations of vessels.

- -

- -

Large fixed steel

Footings

A, E01, 12.4: Over time the steel structure would corrode, but the corrosion products would be largely inert and not bio-available, and would not impact the local benthic or pelagic communities.

Interactions with cuttings A, E01, 12.4: The long-term presence and eventual collapse of the

[structure] would have a bearing on the fate and long-term impacts of the cuttings pile were it to be left in situ. A, E01, 10.5: Disturbance of the pile would result in the release of contaminants into the water column and onto the surrounding seabed.

Following such disturbance, contaminants are likely to be bioavailable to marine organisms in the water column and benthos. A, E01, 10.5: Disturbance of the pile [resulting from the depositing of the topside and jacket] would result in the re-suspension of contaminants into the water column and onto the surrounding seabed. A, E01, 10.3: The effects on the water column would be localised and temporary because contaminants would be rapidly dispersed

and diluted.

It is possible that explosives may be used underwater to sever the piles. Underwater explosions cause pressure waves and loud noises that can be damaging or fatal to marine mammals, finfish and plankton. Some measures to mitigate

against this are available.

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Description and assessment of environmental marine impacts (cont.)

Structure type

Structure Component

Assessment


reference scenario

Assessment


reference scenario

Assessment


reference scenario

Reference scenario Leave in situ with remedial action (P3) Removal and reprocessing of pipelines (P2) Bury and leave pipelines (P4)

General

Pipelines

A, E01, 12.9: The presence of

[decommissioned pipelines left in situ] and its slow degradation would not result in any significant impacts to the seabed or the pelagic or benthic communities.

A, E01, 12.9: A small area of the seabed where remedial action is

required would be disturbed, and the benthic communities there would be

destroyed.

- -

- -

A, E01, 12.9: Would result in a small number of minor impacts to the seabed and benthic communities immediately adjacent to the pipeline. Where pipelines are buried by part of the cuttings pile, some contaminated sediments would be dispersed into the water column, but these impacts would be localised and transient.

- -

- -

A, E01, 12.9: A small area of the seabed along the length of the

pipeline would be disturbed, and the benthic communities there would be destroyed. Where pipelines are buried by part of the cuttings pile, some contaminated sediments would be dispersed into the water column, but these impacts would be localised

and transient.

- -

- -

Excavate & leave (C2) Cover (C3) Removal operations (C4)

General

Cuttings

A, E01, 12.5: The pile

would remain in existence, and ecologically

essentially sterile, for at

least 1,000 years. Presently, the piles are causing only a minimal impact in the adjacent water column and

surrounding benthos, but storm events could cause a

faster release of contaminants.

- -

A, E01, 10.7: Excavation of the pile would create a surface slick of oil that would be evident for the duration of operations, and could impact seabirds and sea mammals in the area. The resettlement would have measurable effects on the benthos by smothering organisms and reducing the diversity of communities over a wide area.

- - -

- (- -)

A, E01, 12.6: The covering operation would result in the re-suspension of small amounts of cuttings and oil into the water column and the subsequent resettlement of cuttings onto the seabed. It is possible that some clean areas of seabed could be impacted by the resettlement of oily

cuttings, and that chemical and biological perturbation resulting from the presence of the cuttings pile could be increased.

-

+

A, E01, 12.7: A limited plume may be generated. Some operational upsets, such as a back-flush event from the suction dredge, may result in the discharge of cuttings into the water column and this could cause limited impacts to benthos and

pelagic organisms.

- +

Reference scenario (CON 01) Remove and reprocess (CON 02)

Concrete

Tank

B, 106: There are considered to be no, or no significant, effects of leaching from the concrete and the reinforcement rods of the Ekofisk Tank into the sea and ground. The overall environmental impact of discharges to the sea is assessed as small and negative.

A, 108: The expected scale of the environmental impacts of releases of seawater and gravel/rock connected with removal of the Tank is assessed

as small.

- -

- -

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Table 5.7: Evidence for the Assessment of Landfill Impacts

Footings

Material, tonnes (t) Mass, M MH MB LIF

Cement grout 650 0 0 650

Marine growth 350 0 350 700

TOTAL 1,000 1,350

Jacket


Marine growth 700 0 700 1,400

TOTAL 700 1,400

Topside


Inert landfill 33 33

Active landfill 211 0 211 422

Hazardous 5 5 0 10

TOTAL 249 465

Whole large steel structure


Cement grout 650 0 0 650

Marine growth 1,050 0 1,050 2,100

Inert landfill 33 0 0 33

Active landfill 211 0 211 422

Hazardous 5 5 0 10

TOTAL 1,949 3,215

Pipelines


Concrete 224 0 0 224

TOTAL 224 224

Cuttings


Cuttings 38,587 38,587 38,587 115,762

TOTAL 38,587 115,762

Concrete structure


Cuttings 80,000 0 0 80,000

TOTAL 80,000 80,000

LIF = Landfill Impact Factor (see Section 5.1.7)

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6. SUMMARY OUTCOMES

6.1 INTERPRETATION OF SUMMARY OUTCOME MATRICES

There now follow summary outcome matrices for each of the decommissioning scenarios that has been analysed in any detail. These matrices are complex. They are interpreted verbally in the text in subsequent sections, which accompany the matrices. However, some preliminary remarks about the matrices may serve to clarify them. Three colours (in addition to black) have been employed in the matrices:

• Material flows are in red.

• Energy flows are in blue. o The Total Energy Requirement (TER) is the total of all the energy requirements, including the energy required to generate the material to replace any material left offshore, which would have been recycled if returned to shore.

o As noted above, TER does not include any energy that might be required for monitoring in the non-reference scenarios that leave material on the seabed.

o The electricity required to dismantle the structure onshore is solely considered in the TER column, as electricity is not a direct material input. Therefore, the sum of the energy inputs shown in the summary matrices do not equate to the TER for return to shore scenarios requiring dismantling.

• Financial expenditures are in green. o ‘Gross expenditure of scenario’ is the total cost of the entire decommissioning scenario to the partnership of owners of the facility.

o ‘Expenditure net of recovered materials’ is the gross expenditure of the scenario less the value of any recovered material.

o ‘Additional cost to UK tax payer’ is the foregone direct tax revenues to the UK Treasury relative to the reference scenario, which is estimated to be 50% of the additional expenditure of the scenario.

• The assessments of non-financial outcomes are in the form described in Section 5. o These refer to impacts not captured by any of the financial expenditures. o The assessments are relative to the reference scenario. The exception to this in each scenario are the columns under the heading ‘Endpoints of structural material’, which describe the quantities of material left in situ, replaced or recovered (and associated energy use), with the rate of recovery, where relevant.

o Some of the assessments are made for impacts which are partly captured by a financial expenditure, and are partly a non-financial outcome (e.g. landfill); this assessment is for that proportion of the impact not captured by the financial expenditure.

o All symbols in the summary matrices are aligned vertically rather than horizontally.

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• An implicit valuation of all the non-financial outcomes relative to the reference scenario is provided by the additional expenditure of a scenario, were it to be adopted by society. This is discussed in each case in the text accompanying the matrices. It may be stressed again that the ‘+’ & ‘-‘ assessments cannot be summed across the different issues as they are incommensurate.

6.2 SUMMARY OUTCOMES FOR TOPSIDE OF LARGE STEEL STRUCTURE (SEE TABLE 6.1)

The reference scenario for the topside (T1) of a large steel structure is to leave it in situ. This involves abandoning 20,520 tonnes (t) of materials, of which 20,271t have to be replaced, with an energy use of 12,523 toe, with associated emissions of CO2, NOx and SO2 as shown in the table. The non-financial outcomes are the reference against which the other scenarios are compared. The cost of T1 is taken to be £0, but there is an unquantified residual financial liability to the owners for the structure and other materials left in situ. Scenario T2 (removal and shallow disposal of the topside) leaves the same amount of material from the structure in the sea, but requires 3,790t of diesel and 1,188t heavy fuel oil (to provide power to run the topside during the decommissioning process), and 1,200t of temporary steel, as well as 5,060 toe of energy, to carry it out. The 1,200t temporary steel (which is left in the sea) is added to the material which has to be replaced on shore, so more energy is required for recycling. The TER has increased by 5,776 toe (46%) over T1, with proportionately higher associated air emissions. The seabed is not clear (as it was not in T1), and the outcomes for health and safety, marine impacts, conservation and extraction of resources and the fishing industry are all more negative than in T1. The landfill outcome is the same, and fish stocks are likely to have benefited (because the topside was not previously acting as a reef). The additional expenditure of this scenario is £18.6m (£9.3m to UK taxpayer), and the financial liability to the owner for the materials and structure left in the sea remains. Scenario T3 (removal to shore and reprocessing of topside) uses 7,071t (7,279 toe) more diesel fuel than T1 and 1,188 tonnes (1,152 toe) more heavy fuel oil, but saves 7,839 toe by recovering, rather than having to replace, the material. 244t of material (211t of which is active waste) needs to be landfilled in non-hazardous landfill facilities, at a cost of £6,888. There is an additional 5 tonnes of hazardous waste consisting of such material as LSA (low specific activity) radioactive material, PCBs and an estimated 4 tonnes of asbestos which would need to be dealt with by specialist contractors and disposal firms. Cost estimates for managing these waste streams are not available from Case Study A, and would be difficult to predict with any level of certainty without more certain knowledge of how it will be managed, but there is no residual financial liability to the owners for any of this landfilled material. The TER includes electricity used in onshore dismantling of the topside, which is not included in the material inputs column. Therefore, as noted above, the TER in this and the other matrices does not necessarily equal the sum of the energy inputs across the row of the matrix. Of the other non-financial outcomes relative to T1, T3 produces a clear seabed, and clear benefits in terms of the conservation and extraction of resources, and to the

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trawling fishing industry. However, T3 is clearly worse than T1 in respect of fish stocks, and seems marginally worse in terms of landfill and impacts on the marine environment. The additional expenditure of T3 is £30.4m (£15.2m to UK taxpayer).

6.3 SUMMARY OUTCOMES FOR JACKET OF LARGE STEEL STRUCTURE (SEE TABLE 6.2)

The reference scenario for the jacket (J1) of a large steel structure is to leave it in situ. This involves abandoning 9,500t of steel and aluminium, all of which has to be replaced, with an energy use of 7,942 toe, with associated emissions of CO2, NOx and SO2 as shown in the table. The non-financial outcomes are the reference against which the other scenarios are compared. The cost of J1 is taken to be £0, but there is an unquantified residual financial liability to the owners for the structure and other materials left in situ. Scenario J2 (removal and shallow disposal of the jacket) leaves the same amount of material from the structure in the sea, but requires 3,122t of diesel and temporary steel and 2,600 toe of energy, to carry it out. The 600t temporary steel (which is left in the sea) is added to the material which has to be replaced on shore, so more energy (358 toe) is required for recycling. The TER has increased by 2,958 toe toe (37%) over J1, with air emissions increased by an even greater proportion, because of the relative emission intensity of the diesel. The seabed is not clear (as it was not in J1), and the outcomes for health and safety, marine impacts, conservation and extraction of resources and the fishing industry are all more negative than in J1. The landfill outcome, and that for fish stocks, are the same. The additional expenditure of this scenario is £23m (£11.5m to UK taxpayer), and the financial liability to the owner for the materials and structure left in the sea remains. Scenario J3 (removal to shore and reprocessing of the jacket) uses 4,339t more materials and 3,852 toe more energy than J1 in the removal, but saves 5,699 toe by recovering, rather than having to replace, the steel and aluminium. 700t of material (marine growth) needs to be landfilled, at a cost of £21,000, but there is no residual financial liability to the owners. The TER of J3 is only 80% that of J1, but it produces more air emissions, because the emission intensity of offshore diesel use is higher than that of onshore refining. Of the other non-financial outcomes relative to J1, J3 produces a clear seabed, and clear benefits in terms of the conservation and extraction of resources, and to the fishing industry. However, J3 is clearly worse than J1 in respect of health and safety, fish stocks, landfill and impacts on the marine environment. The additional expenditure of J3 is £27.7m (£13.8m to UK taxpayer).

6.4 SUMMARY OUTCOMES FOR FOOTINGS OF LARGE STEEL STRUCTURE (SEE TABLE 6.3)

The reference scenario for the footings (F1) of a large steel structure is to leave them in situ. This involves abandoning 10,300t of steel and aluminium, all of which has to be replaced, with an energy use of 7,512 toe, with associated emissions of CO2, NOx and SO2 as shown in the table. It may be noted that the replacement of the materials for the footings requires less energy than for the jacket (J1), despite the greater quantity of materials involved, because the footings contain less energy-intensive aluminium. The non-financial outcomes of F1 are the reference against which the other scenarios are compared. The cost of F1 is taken

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to be £0, but there is an unquantified residual financial liability to the owners for the footings left in situ. Scenario F2a (removal of the footings but leaving the drill cuttings in situ, with no distinction made between cutting the footings at the level of the cuttings and removing them entirely) requires 4,201t of diesel and temporary steel and 3,608 toe of energy to recover the materials, but saves 5,104 toe by recovering, rather than having to replace, the steel and aluminium. 1,000t of material (cement grout and marine growth) needs to be landfilled, at a cost of £21,550, but there is no residual financial liability (for the footings, though that for drill cuttings will remain) to the owners. The TER of F2a is only 85% that of F1, but it produces more air emissions. Of the other non-financial outcomes relative to F1, F2a does not produce a clear seabed (because the cuttings are left in situ), and is clearly worse than F1 in terms of health and safety, impacts on the marine environment, landfill and fish stocks. However, F2a is clearly better than F1 in terms of the conservation and extraction of resources, and in respect of the fishing industry. The additional expenditure of F2a is £26.5m (£13.3m to UK taxpayer). The material and energy outcomes of Scenario F2b (removal of the footings and the drill cuttings to shore) are taken to be the same as F2a, the extra materials and energy required to remove the cuttings being assigned to the cuttings decommissioning scenario. A difference between F2b and F2a is that in F2b there is no residual financial liability to the owners for either the footings or drill cuttings. The TER of F2b is the same as that of F2a. The other non-financial outcomes of F2b are similar to F2a, except that now there is a clear seabed (the fate of the cuttings is considered under the cuttings decommissioning scenario), and more benefits to the fishing industry. The additional expenditure of F2b is the same as that of F2a.

6.5 SUMMARY OUTCOMES FOR ENTIRE LARGE STEEL STRUCTURE (SEE TABLE 6.4)

The reference scenario for the entire large steel structure is to leave it in situ, combining the three in situ references scenarios for the individual components of the structure (T1, J1, F1). This involves abandoning over 40,000t of metals, all of which has to be replaced, with an energy use of 27,976 toe, with associated emissions of CO2, NOx and SO2 as shown in the table. The non-financial outcomes are the reference against which the other scenarios are compared. The cost of this reference scenario for the whole structure is taken to be £0, but there is an unquantified residual financial liability to the owners for the structure (and any other materials left in situ). The next whole-structure scenario to be considered is the removal and shallow disposal of the topside and jacket (T2, J2), while leaving the footings in situ (F1). This leaves the same amount of material from the structure in the sea, but requires 9,300t of diesel and temporary steel and 7,760 toe of energy, to carry it out. The 1,800t temporary steel (which is left in the sea) is added to the material which has to be replaced on shore, so more energy is required for recycling. The TER has increased by 8,734 toe (31%) over the whole-structure reference scenario, with proportionately higher associated air emissions. The seabed is not clear (as it was not in the reference scenario), and all the other non-financial outcomes are worse than in

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the reference scenario, except for landfill, which is the same, and fish stocks, which benefit from the reef effects of the shallow disposal. The additional expenditure of this scenario is £41.6m (£20.8m to UK taxpayer), and the financial liability to the owner for the materials and structure left in the sea remains. Removal of the whole structure to shore for reprocessing (T3, J3, F2a,b) uses 17,998t more materials and 15,896 toe more energy than the whole-structure reference scenario (TI, J1, F1), but saves 18,642 toe by recovering, rather than having to replace, the metals. 1,949t of material (the sum of that from T3, J3, F2a,b) needs to be landfilled, at a cost of £49,348, but there is no residual financial liability to the owners. The TER of this scenario is only 94% that of the whole-structure reference scenario, but it produces more air emissions. Of the other non-financial outcomes relative to this reference, this scenario produces a clear seabed, and clear benefits in terms of the conservation and extraction of resources. It is also positive for the fishing industry. However, the scenario is clearly worse than the reference in respect of health and safety, fish stocks, landfill and impacts on the marine environment. The additional expenditure of the scenario is £84.6m (£42.3m to UK taxpayer).

6.6 SUMMARY OUTCOMES FOR A MOSTLY CONCRETE STRUCTURE (SEE TABLE 6.5)

The reference scenario (CON1) for the mostly concrete structure is to leave it in situ. This involves abandoning over 1mt of materials, 46,134t of which are metals, while the rest is ballast and concrete. Most of this has to be replaced onshore, with an energy use of 30,649 toe, with associated emissions of CO2, NOx and SO2 as shown in the table. The non-financial outcomes are the reference against which the other scenarios are compared. The cost of this reference scenario for the whole structure is taken to be £0, but there is an unquantified residual financial liability to the owners for the structure (and other materials left in situ). The scenario CON2 entails removing the structure to shore for reprocessing. This uses 61,204t (63,005 toe) more diesel fuel than CON1, but saves 20,718 toe by recovering, rather than having to replace, the materials. 83,700t of material (80,000t of which is concrete, the rest being marine growth) needs to be landfilled, at a cost of £1.47m, but there is no residual financial liability to the owners. The TER of CON2 is 189% more than that of CON1, and air emissions are also much greater (though less than proportionately), due to the high energy requirement of recovering the materials. Of the other non-financial outcomes relative to this reference, CON2 produces a clear seabed, and clear benefits in terms of the conservation and extraction of resources. It is also positive for the fishing industry. However, the scenario is clearly worse than CON1 in respect of health and safety, fish stocks, landfill and impacts on the marine environment. The additional expenditure of the scenario is £286.7m (£143.4m to UK taxpayer).

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6.7 SUMMARY OUTCOMES FOR PIPELINES (SEE TABLE 6.6)

Outcomes for four decommissioning scenarios for large pipelines are summarised in Table 6.6. The reference scenario (P1) is to leave them in situ with no remedial action. This involves abandoning 5,351t of materials, 5,127t of which have to be replaced onshore, with an energy use of 2,386 toe, with associated emissions of CO2, NOx and SO2 as shown in the table. The non-financial outcomes are the reference against which the other scenarios are compared. The cost of this reference scenario for the whole structure is taken to be £0, but there is an unquantified residual financial liability to the owners for the materials left in situ. The scenario P2 entails removing the pipelines to shore for reprocessing. This uses 2,046t (2,107 toe) more diesel fuel than P1, but saves 1,578 toe by recovering, rather than having to replace, the materials. 224t of concrete needs to be landfilled, at a cost of £3,808, but there is no residual financial liability to the owners. The TER of P2 is 28% more than that of P1, but air emissions, especially of NOx, are proportionately much higher than this, because of the NOx intensity of burning the diesel. Of the other non-financial outcomes relative to P1, P2 produces a clear seabed, and clear benefits in terms of the conservation and extraction of resources. It is also positive for the fishing industry, and no worse than P1 for health and safety and fish stocks. There is a small negative outcome in respect of landfill and impacts on the marine environment. The additional expenditure of the scenario is £19.9m (£10m to UK taxpayer). The scenario P3 entails leaving the pipelines in situ with remedial action. This uses only 259t (267 toe) more diesel fuel than P1, but leaves the same amount of material in the sea, and the same amount to be replaced, and leaves residual financial liability for owners. The TER of P3 is 11% more than that of P1, but extra NOx are again proportionately much higher than this (though less than in P2). Of the other non-financial outcomes relative to P1, P3 is only an improvement in respect of the fishing industry, is the same in respect of health and safety, fish stocks and landfill, and is worse in respect of natural resources and the marine environment. The additional expenditure of P3 is £1m (£½m to UK taxpayer). The scenario P4 entails trenching and burying the pipelines. It is very similar to P3, leaves the same amount of material in the sea, and the same amount to be replaced, although the pipelines are now covered, and leaves residual financial liability for owners. It uses 920t (947 toe) more diesel fuel than P1. Its TER is 40% more than that of P1, with higher emissions, with extra NOx again proportionately much more increased. Air emissions are also greater than P3, though less than P2. The other non-financial outcomes are the same as for P3. The additional expenditure of P4 is £25m (£12.5m to UK taxpayer).

6.8 SUMMARY OUTCOMES FOR DRILL CUTTINGS (SEE TABLE 6.7)

Outcomes for four decommissioning scenarios for drill cuttings are summarised in Table 6.7. The reference scenario (C1) is to leave them in situ with no covering. This involves abandoning 40,000t of materials, but the great majority of these are waste materials, and only 1,413t of recoverable waste oil (contained in the cuttings) have to be replaced onshore. There

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is no energy use or air emissions in C1. The non-financial outcomes are the reference against which the other scenarios are compared. This is the only reference scenario which is given a negative impact on the marine environment (‘- -‘), because of the long-term ecological sterility of the cuttings pile and the continuous low-level leaching of contaminants from it.The cost of this reference scenario for the whole structure is taken to be £0, but there is an unquantified residual financial liability to the owners for the materials left in situ. The scenario C2 entails excavating and leaving the cuttings. This uses only 772t (794 toe) more diesel fuel than P1, but leaves the same amount of material in the sea, and the same amount to be replaced, and leaves residual financial liability for owners. The TER and air emissions of C2 are obviously higher than the zero in this category of C1. Of the other non-financial outcomes relative to C1, C2 is the same in respect of health and safety, landfill, the fishing industry and fish stocks, but worse in respect of natural resources and the marine environment. The additional expenditure of C2 is £5.1m (£2.6m to UK taxpayer). The scenario C3 entails covering and leaving the cuttings (with or without the base of the footings left in place). This uses 4,004t (4,122 toe) more diesel fuel than C1, and about 166,000t of sand and gravel. The same amount of material is left in the sea, and the same amount has to be replaced as in C1, although the cuttings are now covered, perhaps reducing the financial liability for owners. C3 produces far more air emissions than the zero emissions of C1, but also nearly six times the CO2, and higher other air emissions, than C2. Of the other non-financial outcomes relative to C1, C3 is the same in respect of health and safety and landfill, better in respect of the fishing industry, fish stocks and the marine environment, but worse in respect of natural resources, with especially high resource extraction impacts because of the amount of sand and gravel used. The additional expenditure of C3 is £10.3m (£5.1m to UK taxpayer). The scenario C4 entails removing the cuttings to shore for reprocessing. This uses 9,073t (9,340 toe) more diesel fuel than C1, which is partially offset by the 1,413t (1,370 toe) of recovered oil. 38,587t of material needs to be landfilled, at a cost of £655,984, but there is no residual financial liability to the owners. The TER of C4 is 8,036 toe more than that of C1, with correspondingly high air emissions. Energy use is nearly twice, and air emissions are more than twice, those of C3. Of the other non-financial outcomes relative to C1, C4 produces a clear seabed, and benefits in respect of the fishing industry, fish stocks and the marine environment. It is the same for health and safety. However, it is very much worse than C1 in terms of landfill (assuming the cuttings cannot be processed into an inert construction material), and also negative in terms of resource extraction, and resource conservation (because of the extra diesel use). The additional expenditure of the scenario is £38.9m (£19.4m to UK taxpayer). The information and evidence in this section about the different decommissioning scenarios has relied most heavily on one case study, here called Case Study A, with evidence drawn from a limited number of other studies. This reflects the fairly limited experience with decommissioning, especially of large steel structures, in the North Sea to date and therefore the limited availability of relevant data. However, it is clear the conclusions to be drawn from

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the evidence in this study will only apply to decommissioning in the North Sea more widely if Case Study A, and to a lesser extent the other case studies, are representative of other structures to be decommissioned, or other aspects of decommissioning. The next section, following the summary matrixes, explores the extent to which this might be the case.

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Table 6.1: Summary Outcomes for Topside of Large Steel Structure

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Table 6.2: Summary Outcomes for Jacket of Large Steel Structure

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Table 6.3: Summary Outcomes for Footings of Large Steel Structure

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Table 6.4: Summary Outcomes for Entire Large Steel Structure

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Table 6.5: Summary Outcomes for a Mostly Concrete Structure

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Table 6.6: Summary Outcomes for Pipelines

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Table 6.7: Summary Outcomes for Drill Cuttings

7. ASSESSMENT OF THE WIDER APPLICABILITY OF RESULTS

In making its assessment of the different decommissioning scenarios, this study has presented information on the following issues:

Assessed quantitatively (Section 4)

15. Material inputs; 16. Material endpoints (of the material being decommissioned); 17. Total energy requirement (TER); 18. Total gaseous emissions; 19. Financial expenditures;

Assessed qualitatively (Section 5)

20. A clear seabed; 21. Health and safety of personnel directly involved in the decommissioning process; 22. Jobs in the UK; 23. Impacts on the marine environment; 24. Conservation of non-renewable resources; 25. Impacts of resource extraction; 26. Impacts of landfill; 27. Impact on the fishing industry; and 28. Impacts on fish (and other marine life).

The purpose of this section is to explore to what extent the results obtained from a limited range of case study material might be more generally applicable to decommissioning in the UK sector of the North Sea as a whole.

7.1 ASSESSMENT OF THE GENERIC NATURE OF THE LARGE STEEL STRUCTURE RESULTS

This report has relied on a few case studies, and there is little other detailed information about North Sea decommissioning in the public domain. However, it is hoped that the conclusions from this report will be relevant to more structures than just the ones studied. This section explores the extent to which this may be the case. A key group of structures facing decommissioning in the next few years are the larger steel structures which are typically found in deeper water in the Northern North Sea, with footings fixed to the seabed. Those with jackets with masses of greater than 10,000 tonnes (10kt) are eligible to apply for derogation to leave the footings in situ under the rules of the OSPAR convention. Case Study A from this group of structures provided much of the information for this report. Figure 7.1 shows the distribution of jacket masses for all such eligible steel structures, and Case Study A’s place within the distribution. It can be seen that Case Study A is centrally placed (ranked 13th) in the group of 25 structures with jacket masses between 10kt and 20kt. A further 8 structures have masses of over 20kt.

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Figure 7.1: Distribution of Jacket Masses: UK Structures Eligible for OSPAR

Derogation 98/3

0

10

20

30

40

50

1 3 5 7 9 11

Case study A 15 17 19 21 23 25 27 29 31 33

Structure

Jacket mass (kt)

Source: UKOOA 2001, Appendix II, Page 23 Note: The heaviest structure (ranked 33rd) is beyond the range of the Y-axis at 88kt as it has a large quantity of concrete within the jacket.

Figure 7.2: Distribution Of Jacket Depth: UK Structures Eligible For OSPAR

Derogation 98/3

Case study A

0

20

40

60

80

100

120

140

160

180

200

1 4 7 10 13 16 19 22 25 28 31

Structure

Water depth (m)

Source: UKOOA 2001, Appendix II, Page 23 Note: Data on water depth is not available for one of the 33 large steel structures on the UKCS

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Figure 7.2 shows that in terms of water depth Case Study A, in about 140m of water, is ranked 23rd out of the 32 eligible structures on the UK Continental Shelf (UKCS) for which data is available. 20 structures (ranked 9-28) are in 120-160m of water, and Case Study A is in the middle of this mid-depth distribution. Only 4 structures are in deeper water than 160m. Figure 7.3 combines the data for jacket mass and depth for large steel structures on the UKCS. It shows that the great majority of structures including Case Study A have a mass of between 10kt and 20t and stand in 80-160m of water. Case Study A is at the upper end of the section of the distribution showing a broadly linear, but shallow, relationship between mass and depth. If anything, Case Study A has a low mass in relation to its depth.

Figure 7.3: Jacket Mass Against Depth of Water for Large Steel Structures on the

UKCS

Case study A

0

5

10

15

20

25

30

35

40

45

50

0 50 100 150 200

Depth (m)

Jacket mass (kt)

Source: UKOOA 2001, Appendix II, p.23 Note: A single data point (Harding) has been removed as it stands-out from the rest of the dataset due to its high proportion of concrete, and therefore the results presented in the report are not considered applicable to the decommissioning of the jacket or footings of this structure.

The extent to which results for Case Study A are relevant to other structures is a complex matter, and is determined by a wider set of characteristics than just its mass and water depth, some of which are explored further below. However, these two parameters show that Case Study A can be considered as a mid-range structure in terms of mass and water depth. The topsides of all these structures will tend to be similar in terms of their decommissioning requirements as their design was constrained by the carrying capacity of the lifting vessels available. Clearly there may be important differences in the construction of large jackets, the structures may have worn and weathered differently during their service lives, and additions or modifications will have been made to some of them. Detailed plans for decommissioning

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will obviously need to made for structures on a case-by-case basis, but there is nothing in the basic nature of the structure studied in Case Study A to suggest that the kind of overview results that have been derived for this report would not be more generally applicable to large steel structures other than Case Study A. In fact, this study’s findings would certainly seem to be highly relevant to those structures of similar weight and depth to Case Study A (the majority of large steel structures), although one might expect differences for structures in shallower water or structures that are significantly heavier (see Figure 7.3). The particular nature of the drill cuttings pile in relation to the footings is the key factor that may lead to different conclusions, as discussed in the next section. This conclusion is borne out by the analysis of some further characteristics below.

7.2 ASSESSMENT OF THE GENERIC NATURE OF DRILL CUTTINGS PILE RESULTS

The only available parameter against which the generic nature of the drill cuttings pile results can be assessed is the volume of the pile. A comprehensive comparison of the toxic composition of the cuttings piles would involve a far more complex exercise of interpreting sampling data, which does not exist for the vast majority of cuttings piles on the UKCS. Therefore the hazards particular to each cuttings pile will need to be assessed on a case-by-case basis when decommissioning is being considered. However, the energy, material and financial expenditures required for decommissioning drill cuttings piles are comparable for all cuttings piles of broadly the same size.

Table 7.1: Comparison of Volumes of Case Study Drill Cuttings Pile with Other

Cuttings Piles in the Northern and Central North Sea

Northern North Sea Central North Sea Central and Northern North Sea

Total Volume (m3) 503,218 787,500 1,290,718

Average Volume (m3) 13,978 9,488 11,733

Case Study A (m3) ~25,000 ~25,000

Maximum Volume (m3) 45,000 41,233 45,000

Minimum Volume (m3) 801 252 252

Source: Source: UKOOA 2002, Phase 1, Determination of the Physical Characteristics of Cuttings Piles, using Existing Survey Data and Drilling Information

Table 7.1 shows that the Case Study A cuttings pile, with a volume of about 25,000 m3, is about twice the average volume of piles in the Central and Northern North Sea. Figure 7.4 shows that the cuttings pile volume of Case Study A is ranked 37th out of the 46 structures listed in the source, and is about at the mid-point of the 22 piles larger than 10,000 m3, and there are 24 piles smaller than this. So Case Study A can be considered as towards the upper end of the volume distribution of drill cuttings piles found on the UKCS. In comparison with smaller cuttings piles, the management of the cuttings pile of Case Study A seems likely to provide economies of scale (although it has not been possible to quantify them in this report) in terms of: 1. Any fixed testing, administrative and monitoring costs;

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2. Material required to cover the cuttings pile and therefore the costs and energy requirement of this material; and

3. More general economies of scale associated with handling larger volumes of cuttings. Similarly, further economies of scale might be available in respect of these factors for the cuttings piles larger than that of Case Study A, but it has not been possible to estimate these.

Figure 7.4: Mapped North Sea Cuttings Pile Volumes (000's m3)

Case study A

-

10

20

30

40

50

1 3 5 7 9 11 13 15 17 19 21 23 25 27 29 31 33 35 37 39 41 43 45

Cuttings piles

Mapped pile volume (000's m

3)

Source: UKOOA 2003, Phase 1, Determination of the Physical Characteristics of Cuttings Piles, using Existing Survey Data and Drilling Information - Table 1&2 Notes: Data only available for 46 of the 124 facilities listed.

7.3 COMPARISON OF FINANCIAL EXPENDITURES

In Section 4.1 it was noted that the financial expenditures related to the structure, pipelines and drill cuttings of Case Study A, and the concrete tank of Ekofisk (Case Study B). Because of differences between the structures, and their current condition, extension of these financial expenditures to other structures should be done with great caution and only very broad conclusions drawn from the results. In respect of Case Study A, the calculations for the pipelines costs especially may not representative of the North Sea as a whole. Because Ekofisk is a very particular structure, no extension to other structures has been considered possible, so it has been excluded from Table 7.2. Table 7.2 shows the expenditures that have been calculated in relation to Case Study A, and has scaled these up for the North Sea as a whole to give a very rough estimate of what the various decommissioning scenarios would cost if they were applied to 32 large steel structures (one large steel structure has been excluded, because it is exceptional in containing a large mass of concrete) across the North Sea.

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It can be seen that, with the exception of pipelines (for which trenching and burying is the most expensive scenario), the highest cost scenarios are for removal to shore. If applied across the North Sea, these could entail a total expenditure of £12.2bn (of which over £7bn relates to pipelines10), of which, as has been noted before, around £6bn would be provided by the UK taxpayer through foregone tax revenues. Leaving the footings, pipelines and drill cuttings in situ would save £9bn of this total expenditure, even once monitoring had been provided for. These figures are very rough, but they are of the same order as the £8.8 billion cost for decommissioning estimated by UKOOA and cited in Section 3.1.5, especially when the uncertainty involved in the scaling up of the pipeline estimates for Case Study A is taken into account. Both numbers give an idea of the enormous resources involved in decommissioning and the importance, to both the industry and the public exchequer, of the decisions about derogations of footings, pipelines and drill cuttings that will need to be taken in the not-too-distant future.

Table 7.2: Decommissioning Expenditures for the Different Scenarios Scaled Up

Across the North Sea

Scenario Net Case Study

A expenditure compared to reference, £m

Relevant parameter in scenario

Total for parameter in North Sea1

Scaled up expenditure for North Sea, £m

Remove all to shore

scenarios, £m

T2 18.6 20.5 kt materials 720 kt 653

T3 30.4 20.5 kt materials 720 kt 1,068 1,068

J2 23.0 10 kt materials 353 kt 812

J3 27.7 10 kt materials 353 kt 978 978

F2a 26.5 11 kt materials 397 kt 956

F2b 26.5 11 kt materials 397 kt 956 956

P2 19.9 26 km pipelines 9,400 km 7,195 7,195

P3 1.0 26 km pipelines 9,400 km 362

P4 25 26 km pipelines 9,400 km 9,038

C2 5.1 25 km3 cuttings 1.3 million m3 265

C3 10.3 25 km3 cuttings 1.3 million m3 536

C4 38.8 25 km3 cuttings 1.3 million m3 2,018 2,018 1 For the structural components (topside, jacket, footings) the total mass of 27 large steel structures (1.24mt) was taken from Infield Systems 2000, scaled up by the mean mass to 1.47mt for 32 structures, and divided between topside, jacket and footings according to the ratios for the Case Study A structure

7.4 COMPARISON OF TOTAL ENERGY REQUIREMENT

Tables 7.3a, b compare the decommissioning results for the TER for the total removal scenario for a large steel structure from this study with the results from Case Study A and experience with the decommissioning of Ekofisk. The results from this study are similar to the Case Study A results, not surprisingly, because they are generated by broadly the same

10 Note the earlier remark about the pipeline calculations being particularly specific to Case Study A. The results from scaling up should be treated with special caution in this case.

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model with a similar data set. The Ekofisk results are derived from an aggregate of the decommissioning estimates for 13 smaller steel structures (with no footings), which in total have a greater TER, and greater TER per tonne of material, than the large steel structure represented by Case Study A. For pipelines the situation appears to be different, with the Ekofisk estimates showing its pipeline decommissioning less energy-intensive than those for Case Study A. There are many possible reasons for these differences, including differences in removal techniques or economies of scale (of decommissioning one large structure over 13 smaller ones). Perhaps more significant is the fact that the estimates do not vary by more than about 50%. Comparing the drill cuttings results from this study and Case Study A with those from UKOOA (2002) leads to a similar level of variation in estimates. Perhaps the most important conclusion from this analysis is that not much weight should be attached to differences in energy outcomes from scenarios applied to different kinds of structure if these are less than 50%, because these would seem to be within the possible margin of error of the data.

Table 7.3a Comparison of Different Estimates of Total Energy Requirement (TER)

for the Removal of a Large Steel Structure and Associated Pipelines and Cuttings

Energy – toe This Study Case Study A Scaled Ekofisk UKOOA JIP

Footings 6,351 6,692

Jacket 6,391 6,670 7,654

Topside 13,717 14,333 20,612

Large steel 26,459 27,695

Pipelines 3,062 2,837 2,317

Cuttings 8,036 9,538 6,401

Table 7.3b Comparison of Different Estimates of Total Energy Requirement (TER)

per Tonne of Material Removed for the Removal of a Large Steel Structure and

Associated Pipelines and Cuttings.

Energy – toe/t This Study Case Study A Ekofisk UKOOA JIP

Footings 0.56 0.59

Jacket 0.63 0.65 0.75

Topside 0.67 0.70 1.00

Large steel 0.63 0.66

Pipelines 0.57 0.53 0.43

Cuttings 0.20 0.24 0.161 1 The UKOOA JIP cuttings TER is based on an estimate of 6.7 GJ/tonne (UKOOA 2002, p.23, and Question 66)

7.5 COMPARISON OF OTHER NON-FINANCIAL OUTCOMES

As noted above the other non-financial outcomes that have been assessed (qualitatively) in this study are: clear seabed (or otherwise); health and safety of personnel directly involved in the decommissioning process; jobs in the UK; impacts on the marine environment;

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conservation of non-renewable resources; impacts of resource extraction; impacts of landfill; impact on the fishing industry; and impacts on fish (and other marine life). In respect of these issues, and taking account of the approach that has been taken to them, it seems that Case Study A may differ from other large steel structures more obviously in respect of its decommissioning impacts on the marine environment (and perhaps consequent impacts from landfill), particularly from any decisions that might be taken over its drill cuttings pile. As noted above, drill cuttings piles could vary widely between structures, and each one will need to be the subject to its own analysis. Having said that, none of the evidence submitted has suggested that Case Study A’s drill cuttings pile is either particularly toxic, or particularly environmentally benign, compared to other drill cuttings piles. There is therefore no reason for thinking that the results for Case Study A’s drill cuttings are not a reasonable first estimate of what is likely to be involved in, and the outcomes of, decommissioning drill cuttings piles, certainly until further evidence becomes available. Clearly, however, the paucity of evidence in this area should hedge with caution the kinds of conclusions to be drawn. With regard to all the other non-financial outcomes listed above, there seems no reason not to treat Case Study A as a reasonable point of departure for a broad comparison of outcomes from different decommissioning scenarios as has been carried out here.

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8. CONCLUSIONS

8.1 OVERVIEW OF DECOMMISSIONING ASSESSMENTS AND IMPLICIT VALUATIONS

Table 8.1 presents an overview of all the scenarios that have been discussed, with the non-financial outcomes and the net expenditure of the scenario relative to the reference scenario.

8.1.1 Total energy requirement (TER)

The first broad conclusion, from the TER column, is that taking account of the energy needed to replace materials left in situ makes a difference. Indeed, it is decisive in terms of net energy use for both J3 and F2, which remove the jacket and footings respectively to shore and which use less energy than the reference scenario (because of not having to replace from virgin sources the metals recovered from offshore).

8.1.2 Air emissions

The second conclusion is that air emissions from all the scenarios are worse than in the reference case. This is because offshore diesel use is emission-intensive (especially of NOx - see the summary matrices in Section 6 for the detail of the actual emissions), so that even those scenarios (J3, F2) which use less energy than the reference, produce more emissions.

8.1.3 Clear seabed and resource conservation

A third clear conclusion that emerges from Table 8.1 is the correlation between the scenarios that produce a clear seabed and those that produce positive results in terms of conservation of the stock of non-renewable resources and resource extraction. This is not surprising, as much of the material removed to shore is recyclable metals. The exception is C4, because the drill cuttings contain very little useful material for recycling (the data was not available to the project to assess the possibility of converting the drill cuttings into an inert cionstruction material). On the other hand, the scenarios that produce a clear seabed also tend to be associated with negative environmental impacts from landfilling, which can be considerable (especially CON2 and C4, as evaluated).

8.1.4 Impact on the marine environment

A fourth clear result is that, compared to the reference, and with the exception of the drill cuttings, all the scenarios have a negative impact on the marine environment, and with some (F2a, C2) this is pronounced. This is because most of the structural material and the pipelines are inert. Leaving it in situ therefore has few implications for the marine environment. Removing it to shore, however, involves extensive industrial activities offshore that can cause environmental disturbance, though in most cases these are only of medium or small scale and are short-lived. The drill cuttings piles are different, because of their long-term ecological sterility and slow leakage of contaminants (with the potential for faster leakage if disturbed) if left in situ uncovered (C1). Both covering (C3) ad removal (C4) are assessed as being relatively positive (compared to the reference scenario) for the marine environment. Excavation (C2) is worse, and is likely to be unacceptable on environmental grounds alone.

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Table 8.1: Overview of Non-financial Outcomes from Decommissioning Scenarios and Associated Net Expenditures (cost),

Compared with Reference Scenario

Scenario TER CO2 NOx SO2 Clear

seabed Residual financial liability

Health &

safety

Marine impacts

Stock of resources

Resource extraction

Land-fill

Fishing industry

Fish stocks1

Net cost, £m (50% UK taxpayer)

T2 - - - - - - - - - Not clear Yes = - - - = - - ++ 18.6 (9.3)

T3 - - - - - - Clear No = - - +++ +++ - + = 30.4 (15.2)

J2 - - - - - - - - - Not clear Yes - - - - - = - - = 23.0 (11.5)

J3 + - - - - - - Clear No - - - - ++ +++ - - + - - - 27.7 (13.8)

F2a + - - - - - - Not clear Yes - - - - - - +++ +++ - - ++ - - 26.5 (13.3)

F2b + - - - - - - Clear No - - - - - +++ +++ - - ++ - - 26.5 (13.3)

T2,J2,F1 - - - - - - Not clear Yes - - - - - - = - - ++ 41.6 (20.8)

T3,J3,F2 + - - - - - Clear No - - - - - - +++ +++ - - + - - - 84.6 (42.3)

CON2 - - - - - - - - - - - - Clear No - - - - +++ +++ - - - + - - - 286.7 (143.4)

P2 - - - - - - - - - Clear No = - - ++ +++ - ++ = 19.9 (10.0)

P3 - - - - - - - Not clear Yes = - - - - = ++ = 1.0 (0.5)

P4 - - - - - - - - - Covered Yes = - - - - = ++ = 25 (12.5)

C2 - - - - - - - - - - - - Not clear Yes = - - (-) - - (- -)2 = = = 5.1 (2.6)

C3 - - - - - - - - - - - - Covered Yes = - - +2 = + + 10.3 (5.1)

C4 - - - - - - - - - - - - Clear No = - - - +2 - - - + + 38.8 (19.4) 1.1.1.1.1.1 1 Also includes some other aspects of marine biodiversity 2 Compared with the C1 impact of ‘- -‘

1.1.1.1.1.2 Key to Scenarios All 1 scenarios are reference scenarios Leave in situ T: Topside T2 Removal and shallow disposal; T3 Return and reprocess on shore (applicable to all structures) J: Jacket J2 Removal and shallow disposal J3 Return and reprocess on shore (applicable to large steel structures) F: Footings F2a Remove with cuttings left in situ F2b Remove with cuttings taken to shore (applicable to large steel structures) CON: Mostly concrete structure CON2 Return and reprocess onshore (applicable to concrete structures)

P: Pipelines P2 Remove and reprocess onshore P3 Leave in situ with remedial action P4 Trench and bury C: Drill cuttings C2 Excavate and leave C3 Cover and leave C4 Remove and treat onshore

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8.1.5 UK Employment

No conclusions have been drawn about whether the decommissioning scenarios will provide net employment in the UK. This is not because there is any doubt as to whether decommissioning will employ people in itself. Obviously any major programme of expenditure will directly generate jobs. One issue is that, with an international activity like decommissioning, there is no knowing in advance what proportion of these jobs will be in the UK. The other issue is that the net employment effect of decommissioning will depend not only on the number jobs it directly generates, but the comparison of that number with the number of jobs that would be created by the likely alternative use of decommissioning expenditures (in both the private and public sectors, if some decommissioning expenditures represent foregone tax payments), if decommissioning were not to be carried out. There is no way of knowing what this alternative use of the money might be, nor, in the case of private expenditures, whether they would be spent in the UK. Speculation on these matters has been avoided.

8.1.6 Costly scenarios

Easily the most expensive scenario is CON2, the return to shore of a large, mainly concrete structure. The resources reclaimed are overwhelmingly concrete and ballast, which are not scarce non-renewable resources, although the impacts associated with their extraction can be considerable. This provides the first opportunity for an implicit valuation of a decommissioning outcome. The net environmental benefits of this scenario are a clear seabed, the reclamation of nearly 1mt of materials (920 kt of which were aggregates) and the avoidance of the environmental costs of their extraction, net of the extra air emissions, impacts on the marine environment and fish stocks, and significant extra landfilling involved. While valuations of these environmental impacts may vary between stakeholder groups, it is by no means certain that the net environmental benefits are positive. Other non-financial impacts are a small benefit to the fishing industry and a worse outcome on health and safety. If society were to choose CON2, it would be equivalent to saying that overall it considered these net benefits to be worth £287m in total, and £143m in terms of public expenditure. The next most expensive single scenario is C4, the return of cuttings to shore. This would deliver a clear seabed, with the re-establishment of an ecosystem, in place of the largely sterile and contaminated drill cuttings pile. There would also be a small benefit to fish stocks in terms of the removal of a possible source of toxic contamination. There would also be a benefit to the fishing industry in opening up new grounds to trawling (a development which would certainly remove the direct benefit of this scenario to fish stocks). The environmental costs of this scenario, compared to the reference scenario, are substantial: large scale energy use and air emissions, and maximum negative scores in terms of landfill and resource extraction. Some stakeholders may feel that the achievement of a clear and regenerating seabed is worth both these environmental impacts and the nearly £40m it would cost in the case of this one cuttings pile. Clearing the UKCS of cuttings piles would, as noted above (see Table 7.2), be likely to cost nearer £2bn. Others might feel that the seabed gain is outweighed by the other environmental and the financial costs, that the money, including the roughly 50% of expenditure that would come from the UK taxpayer, could be better spent.

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8.1.7 Covering pipelines

The benefits of covering pipelines (P4) go entirely to the fishing industry, there are a number of negative environmental impacts and it is relatively expensive. P2 is slightly worse in terms of SO2 emissions and landfill, but has clear advantages in terms of resource extraction and the stock of non-renewable resources, achieves a clear seabed and is 20% cheaper. P2 on this assessment therefore seems superior to P4 both environmentally and financially (though it should be remembered that the Case Study A structure to which it applies may not be representative of pipelines around other structures, which may be smaller in diameter and therefore less costly to cover).

8.1.8 Decommissioning the structure

A final set of comparisons can be made in respect of the components of the large steel structures, between those scenarios which envisage their removal to shore (T3, J3, F2a,b) and those that do not (the reference scenarios T1, J1, F1 and the shallow disposal scenarios, T2, J2). The pattern of relative benefits between these scenarios is quite clear. Those that involve removal to shore achieve a clear seabed, conserve the stock of resources and reduce the resource extraction to produce from virgin sources the material that has been recovered. They also benefit the fishing industry. For the jacket and footings the removal scenarios (J3, F2a,b) also conserve energy, although they have more emissions, because of the high relative emission intensity of offshore diesel use. On the negative side, their health and safety implications, and their impacts on the marine environment and in terms of landfill are worse than the in-situ scenarios, which also benefit fish (except for T3) rather than the fishing industry. The removal scenarios are, not surprisingly, more expensive, by £20-30m for each of the three components, or by about £85m overall, compared to the reference scenarios, but by much less (only £4.7m between J2 and J3) compared with shallow disposal. Moreover, all the in-situ scenarios involve some degree of monitoring, which, as noted above, is a cost and has a small environmental impact which have not been included in the assessment. A financial (though unquantified) benefit of all the clear seabed scenarios, as far as the industry is concerned, is that they extinguish any residual financial liability. It may well be that the industry would be prepared to pay its share (on average around half) of the cost of the removal scenarios in order to be free of any future liability. Whether this consideration counts as much for the UK taxpayer, who may prefer to live with the liability while it is not proving problematic, and put the taxation revenues to another use, is another matter.

8.1.9 Deciding on Drill Cuttings Piles

As noted earlier, it is only in respect of the drill cuttings piles that the reference scenario (C1) may result in a significant negative effect on the marine environment. Excavation (C2) will have an even greater negative effect on the marine environment and is not likely to be seriously considered on these grounds alone. Both C3 (covering) and removal (C4) have been assessed as having a positive effect on the marine environment compared with C1. The major environmental impact associated with C3 is the very large quantity of aggregates (166,000t) that is required. This produces a large negative impact in terms of resource extraction. It may also be noted that this material is not included in the definition of the ‘resource stock ratio’ (RSR, see Section 5.1.5), according to which the entry under ‘Stock of resources’ in the

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summary outcome matrices is calculated. Had it been so, then C3 would have scored a ‘- - -‘ in this category as well. The small benefit of C3 to fish stocks would, as with C4, be swiftly removed by the fact that it would open up the area to the fishing industry. C3 has clear environmental benefits over, for example, C2, because the cuttings are covered rather than excavated (blown away). Its marine environmental benefits are comparable to that of C4 (removal); it uses less fuel and has no landfill implications, but requires far more aggregates; it is also less than a third of the cost of C4. The implicit valuations in relation to the drill cuttings scenarios may therefore be summarised as follows: C1: this would place a value of less than £10m on the net C3 environmental benefits, and

less than £39m on the net C4 environmental benefits C3: this would imply that the C3 seabed benefits (compared to C1) less the negative

impacts of the extra fuel use and aggregates extraction were worth at least £10m C4: this would imply that the C4 seabed benefits (compared to C1) less the negative

impacts of the extra fuel use and landfill were worth at least £39m

8.2 THE DIFFERING PERCEPTIONS, PREFERENCES AND PRIORITIES OF DIFFERENT

STAKEHOLDERS

8.2.1 A spectrum of views

The difference in preferences and priorities noted in the previous paragraph is an example of the many such differences that are undoubtedly involved in the issue of decommissioning, which is one of the reasons why any attempt to give unique money values to the different impacts and outcomes is likely to be unsatisfactory, and why there is unlikely to be a full social consensus on the ‘best’ decommissioning scenario. Watson (2004) has expressed the opinion that there are at least seven different kinds of consideration which will influence the attitude to decommissioning of different stakeholders: technical feasibility, safety, cost, environmental impacts, the regulatory framework, reputation and the political environment. As noted earlier (Section 1.1), the attitude of Greenpeace (2004) to some of these issues was that any full consideration of decommissioning also needs to take account of broader issues such as “the established international trend against dumping”, “the cumulative damage and the potential precedent that could be set by dumping individual installations on a ‘case-by-case’ basis”, the need for industry to take responsibility for the products it creates, the precautionary principle and the need to protect the environment from harm. While the views of Greenpeace may not be representative of other environmental groups, or of society at large, it is certainly the environmental group that has exerted most influence on the UK decommissioning debate and on decommissioning policy, which is why its views have been singled out for consideration here. Greenpeace (2004) considers that full removal of all materials to shore is technically feasible (and cites the contractors who would get the work to that effect), and that risks to personnel in the activities involved can be mitigated. This contrasts with those in the industry who consider that the limited decommissioning experience to date has shown that significant technical difficulties remain (Watson 2001, p.28) and, of course, dangerous activities remain potentially dangerous whatever risk mitigation measures are taken, and accidents happen. In any case, driving risks down to very low levels, in a context of considerable technical uncertainty in the first place, is bound to

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increase costs, perhaps very substantially, above the already uncertain estimates that have been quoted here. No evidence has been found that Greenpeace is concerned about the high costs of decommissioning, which, as noted extensively above, will be shared between the industry and the UK taxpayer (from foregone tax revenues, as explained earlier). Rather it tends to stress the need to reinforce the international trend against dumping and the need for the industry to take responsibility for its products, implicitly whatever the cost. In contrast, the industry is certainly likely to worry about costs, but this will not be the only consideration. It might well be prepared to pay its (half) share of the costs of the removal scenarios, in order to remove any question of future liability and protect its reputation. The Government (and taxpayer) may have a different view as to whether this is the best use of public money. Industry will also tend to worry more about safety (it is easy to say that risks must be mitigated, but, as noted above, accidents happen and are also bad for reputation) and about the technical feasibility of removing tens of thousands of tonnes of material from relatively deep water. Contractors will tend to be optimistic about this feasibility, because they will be paid to solve any problems that may arise. The industry is bound to worry about the time and cost uncertainties that may be involved. There is also the possibility that, again for reasons of reputation, the industry may not wish to challenge the current regulatory framework, again preferring to pay its (half) share of the bill for total removal to buy political peace. Again, it is not clear, on the basis of this assessment, that such an outcome would be in the public interest, either environmentally or for the taxpayer. The environmental outcomes from the various decommissioning scenarios are mixed. No scenario can be said to be definitively superior from an environmental point of view. The total removal scenarios can only be justified environmentally if a relatively high value (though differing for different scenarios) is put on a clear seabed, benefits to the fishing industry, the conservation of the stock of resources and the impacts of resource extraction (although the last two considerations do not apply to drill cuttings), and a relatively low value is put on fish (for all the scenarios), energy use and air emissions (for the concrete structure and drill cuttings), impacts on the marine environment (for all the removal scenarios except drill cuttings) and landfill (especially for the drill cuttings). It is not clear that this would be the relative valuation accorded to these issues either by the range of environmental groups concerned about the marine environment, or by society more widely. It is also not clear what action might be most in line with the precautionary principle, which Greenpeace has said needs to be taken into account. Avoiding the negative environmental impacts from the removal scenarios may be as important in this regard as achieving a clear seabed and recycling metals none of which can be regarded as scarce.

8.2.2 The authors’ assessment

In the view of the authors, a balanced and independent assessment of the considerations above might arrive at the following tentative conclusions. Topsides For the topside, all parties seem agreed that removal to shore (T3) is the only scenario worthy of serious consideration, and the assessment shows this to have fewer environmental trade-offs than some other removal scenarios. It still involves expenditure of some £30m (£15m

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from the taxpayer) for a single large steel structure, £12m more than the shallow disposal scenario (T2). Jackets of large steel structures

For the jacket, the same arguments seem to apply, except that the difference in cost between the removal (J3) and shallow disposal (J2) scenarios is significantly less. As has been noted throughout, both the reference (T1, J1) and shallow disposal (T2, J2) scenarios are illegal under the current DTI regulations deriving from the OSPAR 1998 Decision. This assessment shows the implementation of these regulations to be far from cheap, for the industry or the UK taxpayer, but, although mixed environmentally, the regulations are at least not obviously counter-productive, and they implement the desire articulated by Greenpeace (which may well have support more widely among the UK and European public) that industry should clean up after itself and take responsibility for its products. It is possible that the use of a decommissioned structure as an artificial reef could be sanctioned as a ‘legitimate use’ of the structure, rather than its disposal, but there is little doubt that any attempt to obtain such a sanction would be widely seen as a challenge to the OSPAR 1998 Decision, for which at present there seems to be little appetite in any quarter. Footings of large steel structures

The footings are a different matter, largely because of their difficulty of removal, causing both environmental impacts and safety concerns, the former of which are complicated by the footings’ interaction with drill cuttings. The major impact of leaving them in situ is on the fishing industry. Their removal across the UKCS could cost nearly £1 billion (see Table 7.2), of which about one half would be paid by UK taxpayers. It is not at all clear to the authors that this expenditure would represent good value for money. Large concrete structures

Unlike the large steel structure, there are strong arguments, environmental and financial, for not removing large concrete structures to shore (CON2), and few environmental arguments for doing so. The taxpayer expenditure alone on this scenario (£143m) would not, in the view of the authors, be justified by the benefits that would result11. Drill cuttings piles

The situation with drill cuttings is the most complex of the components of decommissioning studied, as has been clearly shown by the assessment and implicit valuation in Section 8.1.9. Excavation (C2) may be rejected on environmental grounds, but both the removal (C4) and covering (C3) scenarios also have significant environmental impacts of their own, and require substantial expenditures from both the industry and the taxpayer. For some people, this expenditure, in order to clear the seabed of materials that are affecting around 0.15% of the seabed of the North Sea, and the ongoing pollution risk which seems rather small, this expenditure will seem excessive. The UKOOA Joint Industry Project (JIP) Report, which has already been extensively cited, stated that, as long as the rate of loss of hydrocarbons from a cuttings pile to the water column was less than 10 t/year, and the area of seabed with

11 This was the view also taken by the Norwegian Parliament in 2002, when it approved the ConocoPhillips plan for decommissioning Ekofisk, involving the in-situ disposal of the large Ekofisk tank, which was the subject of the financial calculations above. The plan also entails the removal of the 14 steel topsides of the Ekofisk complex (including that of the tank), and the leaving in situ of the buried pipelines and drill cuttings (ConocoPhillips 2002)

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hydrocarbon concentrations of greater than 50mg/kg over time was less than 500km2years, allowing the natural degradation of cuttings piles would the best environmental strategy (UKOOA 2002, Final report p.36). For the two cuttings piles examined in the project (Beryl A and Ekofisk 2/4 A) the rate of loss of hydrocarbons to the water column was around 5 t/year (UKOOA 2002, Final report, p.26), which clearly satisfies at least the first condition for natural degradation to be the best environmental strategy. The independent Scientific Review Group (SRG) of the UKOOA JIP was more equivocal and advocated a case-by-case approach for each drill cuttings pile: “We support the conclusion that the most suitable options are removal, covering, and leaving in place to allow natural degradation, and that the balance of advantage between these will depend on the specific characteristics and the environment of individual cuttings piles.” (SRG 2002, p.4) The SRG then recommends the re-injection of drill cuttings in cases where removal is the preferred option. However, in Section 3.5 this was shown to be as expensive as onshore processing and to be potentially problematic both logistically and in relation to OSPAR prohibitions against dumping at sea. The conclusions of the Independent Review Group (IRG) of the Case Study A work in this area were quoted at some length in Section 3.5 and will not be repeated, except to note that they were no more definitive than those of SRG. The Case Study A work did not allow this project to assess the options of re-injection, bioremediation or processing into an inert construction material in detail. However, on the basis of the information and technologies currently available, a very high value would have to be put on a clear seabed, and a low value on the negative environmental impacts of the alternatives, for the preferred scenario not to be leaving the cuttings in place, with a monitoring programme (see below) to keep their condition and any pollution from them under review. Pipelines

For pipelines the situation is similar to that for footings. Recovering them (P2) clears the seabed, conserves resources and reduces the impacts of resource extraction, but with some environmental impacts, and at a cost of £20m (a figure which, as noted above, is specific to Case Study A and may not be representative). The main beneficiaries of this expenditure, as with clearing footings, would be the fishing industry. Covering the pipelines (P4) is even more expensive and has little environmental justification over removal. Leaving them, with remedial action to make them safe for fishing if necessary, would be the preferred scenario, unless a very high value was put on a clear seabed and the resources they comprise. Monitoring material left in situ

As noted above (Section 5.2), all scenarios with material left in situ would require monitoring, the financial and (small) environmental implications of which need to be added to the relevant scenarios. This monitoring, and the financial implications of any remedial action which it revealed to be necessary, would, in the first instance, be the responsibility of the industry, in view of the ongoing liability for materials left in situ which it would retain. It was outside the scope of this project to investigate the institutional design of any monitoring programme (for example, who should take the decisions about the frequency of monitoring, or what conditions would trigger a requirement for remedial work on, perhaps, the drill cuttings piles). However, the very existence of such a monitoring programme raises the possibility of this monitoring being combined with marine monitoring for other purposes, which in turn broadens the scope of consideration beyond decommissioning.

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8.3 PUTTING DECOMMISSIONING INTO A WIDER CONTEXT

Decommissioning is not the only activity in the marine context with environmental implications. Indeed, according to OSPAR, the offshore oil and gas industry is not responsible for any of the six human pressures on the marine environment to which it gives a Class A (highest impact) grading (three of the six pressures come from fishing [removal of target species, seabed disturbance, effects of discards and mortality of non-target species], two of them are trace organic contaminants from land and shipping, and one is inputs of nutrients from land) (OSPAR 2000, Table 6.1, p.113). In this context, any decommissioning scenario that preserves areas from fishing (as the oil and gas structures have done) seems likely to have additional environmental benefit (as noted above). Put another way, if a seabed clear of drilling materials resulting from decommissioning means that trawling again takes place over the area, the seabed will very soon become clear of most marine environmental interest as well. One response to marine environmental degradation, and the loss of fish stocks, has been proposals to establish marine protected areas (MPAs, RCEP 2004, Gell & Roberts, forthcoming). OSPAR itself is currently engaged in efforts “to complete by 2010 a joint network of well-managed marine protected areas that, together with the Natura 2000 network, is ecologically coherent.” (OSPAR 2003, para.11). MPAs established to conserve or rebuild fish stocks would need to be substantially larger than those currently being considered for nature conservation purposes. However, were these larger MPA to include the current sites of oil and gas installations, this would remove the risk of any drill cuttings piles left in situ being disturbed by trawling operations, with a consequent release of pollution, and would permit any covering of these piles, to enable ecosystem regeneration on the seabed, to be far less robust. The present simultaneous concern with both decommissioning and MPAs would seem to open up a significant opportunity for marine environmental protection that embraces both issues. One of the factors that militate against MPAs is the expense of monitoring them. Monitoring is necessary both to ensure that their status and regulations (e.g. no fishing) are being observed, as well as to determine scientifically whether protecting the area is having the desired environmental results. It is here that the potential synergies with some decommissioning scenarios exist. It has been noted above that, in respect of footings, pipelines and drill cuttings at least, the net environmental benefit of removing all materials to shore is uncertain, while the cost is very large. If these materials were to be left offshore, they would need monitoring. This monitoring would be paid for by the industry as part of the decommissioning scenario. If the area to be monitored was included in an MPA, it could be a relatively simple task to devise a scheme whereby the monitoring also included scientific work and surveillance of MPAs. The potential problem of in-situ decommissioning scenarios, in relation to interfering with fishing gear, would then also not arise, because fishing boats would be excluded from the relevant areas. In time, it might even be that the well-attested reef effects created by the shallow disposal of structures (see Section 5.1.9 for an account of these effects in respect of the existing standing structures) would, in the context of a MPA, make this scenario more publicly acceptable for jackets or topsides, provided that some of the monies saved over their removal to shore were also channelled into monitoring or other marine environmental protection activity related to the MPA.

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It has been noted above that one of the issues relating to in-situ decommissioning scenarios, which makes them unattractive to the industry, is that they involve residual financial liability for the materials left offshore. It may be that, in addition to making a contribution to monitoring, the industry would be prepared to contribute to a marine environmental protection fund, to reduce or share this liability with the Government, which would provide even more resources for marine environmental protection. There can be little doubt, on the basis of the evidence in the assessment above, that using these resources for direct marine environmental protection, especially if this was related to MPAs, would yield far more environmental benefit than the removal of thousands of tonnes of non-scarce materials to shore. The serious consideration of such a proposal would require the various parts of OSPAR (those relating to decommissioning and MPAs) to start bringing these issues together with a view to finding joint solutions to decommissioning and the wider protection of the marine environment. Then there is the added difficulty that fishing is outside the remit of OSPAR altogether, and is handled in the North Sea area by the European Commission, through the Common Fisheries Policy, for EU Member States, and by individual countries otherwise. This introduces great institutional complexity into any potential discussions about a strategy that involves conserving fish as well as the marine environment. However, it should also be noted that such discussions are already taking place in the context of attempts to agree at the EU level a Marine Thematic Strategy, which, among other things, is proposing the establishment by 2010 of Eco-Region Marine Environmental Protection Plans (European Commission 2004). It would seem highly desirable that out of these discussions emerge an effective mechanism to look at such overlapping issues as the possible relationship between decommissioning outcomes and MPAs . The difficulties of establishing such a mechanism should not be underestimated. The reason for attempting to overcome them is that utilising resources from the offshore oil and gas industry that were made available for marine environmental protection as part of a package that combined decommissioning with MPAs for habitat protection and the regeneration of fish stocks could transform the prospects for marine environmental conservation. It is hoped that this report will make a contribution to discussion of these issues.

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47. UKOOA CO/101/01, August 2001, UKOOA working group OSPAR 2003: Issues Summary Paper.

48. UKOOA (UK Offshore Operators Association) 2002, UKOOA Drill Cuttings

Initiative: Final Report, – Joint Industry Project (JIP), Research and Development Phases 1 and 2, 2000, CD re-released in 2002, UKOOA, London http://www.oilandgas.org.uk/issues/drillcuttings/pdfs/finalreport.pdf, also see UKOOA website a, http://www.ukooa.co.uk/issues/decommissioning/links.htm

49. Watson, T. 2001 ‘The Environment and the Decommissioning of Offshore

Installations’, MA Dissertation, Greenwich Maritime Institute, University of Greenwich, London

50. Watson, T. 2003 ‘Removable Feast: New Business Opportunities Through

Decommissioning’, EEEGR Event, November, Newmarket Racecourse, Suffolk, http://eeegr.com/eventmaster/pix/20.

51. Watson, T. 2004 Personal communication, February 25th

104

52. Wills, J. 2000 Muddied Waters: A Survey of Offshore Oilfield Drilling Wastes and

Disposal Techniques to Reduce the Ecological Impact of Sea Dumping, for Ekologicheskaya Vahkta Sakhalina (Sakhalin Environment Watch), 25th May 2000 - http://www.alaskaforum.org/other/muddiedwaters.pdf

105

ANNEX 1: THE REGULATORY FRAMEWORK

Note: The following information about the current regulatory framework in respect of decommissioning has been largely taken from the UKOOA website12.

The process of decommissioning is regulated by international, regional and national legislation. The distinction between the removal and disposal of disused offshore oil and gas installations is important as they come under very different types of legislative frameworks. Whilst interlinked, the legal requirements for removal are primarily concerned with safety of navigation and other users of the sea. The disposal of structures comes under the pollution prevention regulatory framework.

International frameworks and conventions Geneva Convention The current regulations have evolved from earlier conventions such as the 1958 Geneva Convention on the Continental Shelf, article 5 (5) of which called for the total removal of all marine based structures. This international convention came into force long before deep-sea structures were ever emplaced. UNCLOS

The Geneva Convention was superseded by the UN Convention on the Law of the Seas 1982 (UNCLOS), Article 60 (3) of which permits only partial removal of offshore structures provided IMO criteria are met. IMO Headquartered in London, the International Maritime Organisation (IMO) sets the standards and guidelines for the removal of offshore installations world-wide. The 1989 IMO Guidelines require the complete removal of all structures in waters less than 100 metres (since January 1998 – previously it was 75 metres) and substructures weighing less than 4,000 tonnes. Those in deeper waters can be partially removed leaving 55 metres of clear water column for safety of navigation13. All new structures installed after 1 January 1998 must be designed so as to be feasible for complete removal. The London (Dumping) Convention (London Convention)

The London Convention (LC) is based at IMO headquarters in London. The new ‘Guidelines for the Assessment of Wastes and Other Matter that may be Considered for Dumping’ were finalised in September 2000. These Guidelines have been reviewed by a LC Working Group and have now been adopted. The 1972 London Convention made provision for generic guidance for any wastes that can be dumped at sea. These new guidelines provide specific guidance for different classes of waste, including platforms and other man-made waste.

12 http://www.ukooa.co.uk/issues/decommissioning/framework.htm. The DTI Guidelines themselves are available on http://www.og.dti.gov.uk/regulation/guidance/guidenote.doc. 13 This requirement is partially linked to defence requirements. Submarines require a depth of 55m to be able to remain submerged. The requirement does not apply to structures that are not removed and are left protruding above the water line.

106

Regional conventions In addition to the international legislative framework, there are a number of regional conventions which govern marine disposal in specific areas. The North East Atlantic is governed by OSPAR (the area reaches from the east coast of Greenland to the west coast of continental Europe and stretches from the Arctic down to the southern most tip of Europe at Gibraltar). Similar conventions govern other seas such as BARCOM for the Mediterranean and HELCOM for the Baltic Sea. OSPAR

OSPAR is an international convention drawn up in 1992 and which came into force in March 1998. It replaced the 1972 Oslo Convention (on dumping from ships) and the 1974 Paris Convention (on discharges from land) to protect the marine environment of the Northeast Atlantic from pollution. The Convention’s main roles are to control disposal of all waste at sea and discharges from land. There are 16 contracting parties including the UK, and the EU in its own right. Until June 1995, the OSPAR Convention did permit, under certain circumstances, the disposal at sea of parts or all of disused offshore installations. After the Brent Spar affair in June 1995, a moratorium on all disposals at sea of offshore structures was instated (although not formally signed-up to by the UK and Norway). The OSPAR Convention framework works alongside international legislation governing the removal of structures. Therefore, prior to the change to the OSPAR regulations in February 1999, the OSPAR guidelines were only called upon for structures over the IMO’s required size for total removal (ie structures in waters deeper than 100 metres and weighing more than 4,000 tonnes). This accounted for some 80% of the structures in the North Sea. In July 1998, at the OSPAR Ministerial meeting in Portugal (Sintra), the section of the Convention governing the disposal of offshore installations was reviewed and a new regulatory framework – Decision 98/3 – now exists which no longer permits any disposal at sea of offshore structures. OSPAR Decision 98/3 now requires the following:

• all topsides of all structures must be removed to shore;

• all sub-structures or jackets weighing less than 10,000 tonnes must be totally removed and brought to shore for reuse, recycling or disposal ;

• for sub-structures weighing over 10,000 tonnes, an assessment will be made on a case by case basis as to whether they should be totally removed or whether the footings might be left in place; and

• derogation may be considered for the heavy concrete gravity based structures listed in Annex 1 of the Decision as well as for floating concrete installations and any concrete anchor-base which results, or is likely to result, in interference with other legitimate users of the sea.

• exceptions can be considered for other structures when exceptional and unforeseen circumstances resulting from structural damage or deterioration or other reasons which would prevent the removal of a structure

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National and Local Legislation The legislation governing the decommissioning of offshore structures on the UK continental shelf involves a number of different government departments and bodies. All Government departments concerned with decommissioning and with the issuing of any permits or consents co-operate to ensure that their procedures are compatible. The international laws described above are enshrined in the UK’s national legislative framework. The principal legislation for decommissioning comes under the Petroleum Act 1998 which is administered by the DTI and which provides a framework for the decommissioning of disused offshore installations and pipelines on the UKCS. The DTI also provides operators with guidelines on how to undertake the process of decommissioning. These are described in the DTI’s Oil & Gas Directorates draft ‘Guidance Notes for Industry – Decommissioning of Offshore Installations and Pipelines under the Petroleum Act 1998’.

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ANNEX 2: APPROVED DECOMMISSIONING PROGRAMMES

Source: DTI - http://www.og.dti.gov.uk/upstream/decommissioning/programmes/approved Copied from DTI website: 26th February 2004.

Field /

Installation Operator at

time of

Approval

Operator

following

licence /

company

change

Main Installations

Decommissioned Approved

Decommissioning

Option

Year of

Approval

Piper Alpha Occidental Talisman Fixed Steel Platform Toppling 1988

Floating Production, Facility (FPF)

Removal to shore

Catenary Anchor Leg Mooring (CALM) Buoy

Removal to shore

Crawford Hamilton BHP

Subsea Facilities Removal to shore

1991

Floating Production, Facility (FPF

Removal to shore

Catenary Anchor Leg Mooring (CALM) Buoy

Removal to shore

Argyll, Duncan and Innes

Hamilton BHP

Pipelines Removal to shore

1992

Blair Sun Oil AGIP Pipelines 1 x Re-use

1 x Decommissioned in situ

1992

Angus Amerada Hess

Floating Production, Storage and Offloading (FPSO) Vessel

Re-use 1993

Forbes AW Hamilton BHP Fixed Steel Platform Removal to shore 1993

Esmond CP & CW

BHP 2 x Fixed Steel Platform

Removal to shore 1995

Gordon BW BHP Fixed Steel Platform Removal to shore 1995

FPSO Re-use Emerald MSR

Pipelines Decommissioned in situ

1996

Frigg FP Elf Norge TotalFinaElf Norge

Flare Column Removal to shore 1996

Leman BK Shell Fixed Steel Platform Removal to shore 1996

Staffa Lasmo Pipelines Removal to shore 1996

Viking

AC, AD, AP & FD

Conoco 4 x Fixed Steel Platform

Removal to shore 1996

Brent Spar Shell Oil Storage and Loading Facility

Re-use as part of quay extension

1998

109

Donan BP FPSO Re-use 1998

Single Anchor Leg Mooring Buoy

Removal to shore Fulmar SALM

Shell

16" Pipeline Decommissioned in situ

1998

FPSO Re-use Blenheim and Bladon

Talisman

Pipelines Removal to shore

2000

FPSO Re-use Durward and Dauntless

Amerada Hess

Subsea Facilities Removal to shore

2000

Large Steel Gravity Platform

Removal to shore for re-use or recycling

Concrete Loading Column

Removal to shore for re-use or recycling

Maureen and Moira

Phillips

Pipelines 2 x removal to shore

1 x decommissioned in situ

2000

Camelot CB ExxonMobil Fixed Steel Platform Re-use or removal to shore for recycling

2001

Revision to Approved

Decommissioning

Option: Removal to shore for dismantling and recycling

Year of

Revised

Approval:

2002

Durward and Dauntless

Amerada Hess

Pipelines Decommissioned in situ 2002

Tension Leg Platform

Re-use Hutton Kerr-McGee

Pipelines 1 x removal to shore

1 x decommissioned in situ (with future monitoring programme)

2002

Forbes and Gordon Infield Pipelines

BHP Billiton Infield Pipelines Decommission in situ - retrench any area of pipeline with less than 0.4m depth of cover

2003

Frigg TP1, QP & CDP1

Total E&P Norge AS

Treatment Platform 1 (TP1), Quarters Platform (QP) and Concrete Drilling Platform 1 (CDP1)

Concrete substructures to remain in place, Concrete topsides to be removed to shore, Steel installations to be removed to shore, Infield Pipelines to be removed to shore

2003

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