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Using Comparative Assessment Methods to Determine Preferred
Options in Pipeline and Jacket Decommissioning
Presented by
Joe Ferris
BMT Cordah Ltd, Aberdeen, Scotland
and
Johnny Tjea
BMT Asia Pacific, Jakarta, Indonesia
14 August 2015
• Introduction
• Comparative assessment within decommissioning
• Approach taken for North Sea decom programs
• Some of methods used
• Criteria considered
• Examples – A large platform and pipelines
• Conclusions/ recommendations
AGENDA
Unless all infrastructure are to be removed an understanding is needed as to relationship between
• Potential environmental and societal impacts;
• Safety considerations; and
• Costs.
Subsequently various options are considered.
Comparative Assessment (CA) used to evaluate options under consideration against a defined set of criteria and sub-criteria
COMPARATIVE ASSESSMENT WITHIN DECOMMISSIONING
In general three evaluation methods used:
1. Visualisation (A simple qualitative assessment)
• Uses a red-amber-green coding and narrative to describe the difference in performance between the options.
2. Narrative = Scoring + Visualisation
• Scoring based on scales to describe the difference in performance between the options against criteria and uses narrative with visualisations.
3. Narrative = Scoring + Weighting + Visualisation
• Derives scores as above and weights scores resulting in an overall order of preference.
APPROACHES TAKEN WITHIN NORTH SEA DECOM PROGRAMS
Options assessed with respect to five main criteria:
• Safety
• Environmental
• Technical
• Societal
• Economic
CRITERIA AND SUB-CRITERIA
ASSESSMENT CRITERIA SUB-CRITERIA (Matters to be considered )
Safety Risk to personnel
Risk to other users of the sea
Risk to those on land
Environmental Marine impacts , e.g. seabed, discharges, etc.
Other environmental compartments
(including emissions)
Energy/resource consumption
Other environmental consequences
(including cumulative effects and transboundary)
Technical Technical feasibility
Risk of major project failure
Societal Fisheries impacts
Shipping
Communities
Economic Costs
CRITERIA AND SUB-CRITERIA
The set of criteria must be:
• Complete
o It should cover all of the objectives of the stakeholders; covering all aspects of the situation that stakeholders care about when making the decision
• Non-overlapping
o Criteria should be different and independent, to avoid double counting
• Assessable
o It should be possible to assess the options against the criteria, using either data or expert judgement
CRITERIA AND SUB-CRITERIA
EXAMPLE: LARGE PLATFORM
CNRI Murchison Jacket Decommissioning – CA examined complete removal compared with removing the jacket down to top of footings.
• Eight leg structure of welded steel construction
• 75 by 75 m at the base
• 52.8 by 62.5 m at the top
• Overall height of the jacket is 188 m.
• Jacket foundations consist of 32 piles in groups of 8
• Each pile is 82” (208 cm) in diameter and 80 m in length, driven 40 - 50 m into the seabed
• Gross weight 27,584 tonnes (jacket structure + piles + grout + marine growth + flooded members)
EXAMPLE: LARGE PLATFORM
• Technically challenging as the Murchison jacket would be the largest jacket to be decommissioned in the North Sea up to that time.
• CNRI studies included reviews of new and emerging technology to assess whether the new single lift vessel concepts could remove the Murchison jacket as a single lift.
• Full removal and partial removal options evaluated. Both required an intensive period of offshore activity involving a large number of specialist vessels, equipment and personnel.
• Comparative assessment utilized qualitative and quantitative assessments with weightings
EXAMPLE: LARGE PLATFORM
Example of the criteria evaluated
EXAMPLE: LARGE PLATFORM
EXAMPLE: LARGE PLATFORM
CA concluded that there was significant increase in operational safety risk, technical complexity and cost associated with the full jacket removal compared to partial jacket removal.
The comparative assessment identified the following key issues:
• Full jacket removal would increase the Potential Loss of Life (PLL) by 100% compared to the partial removal option.
• Partial removal creates a long term and persistent risk to fishermen from the potential snagging of their fishing gear on the remaining footings.
• Both options cause some environmental disturbance, concluded that this would be localised and of short duration.
• No significant difference in the energy and emissions in the full compared to partial removal options
• Full jacket removal is technically more challenging than partial jacket removal.
• Higher probability of project failure for full jacket removal compared to partial jacket removal.
• Cost of full jacket removal is approximately 75% higher than for the partial removal option
EXAMPLE: PIPELINES
• Southern North Sea CA for infield pipelines included in the proposed Decommissioning Programmes
• 16 pipelines
• Located within a designated conservation area
• The CA would help determine the preferred option for future decommissioning programs
Technical feasibility assessment selected from eleven proposed options, five options for further assessment through the CA process:
Option 1: Full Removal – Reverse S-Lay/ Reel;
Option 2: Full Removal – Cut and Lift;
Option 3: Partial Removal – Cut and Lift;
Option 4: Decommission in place – Minor Intervention; and
Option 5: Decommission in place – Minimum Intervention
EXAMPLE: PIPELINES
Minor intervention relates to the removal of all mattresses, where safe to do so, and rock placement on all exposed sections of the pipeline.
Minimum intervention mattresses will remain in situ, cut pipeline ends would have rock-placement, and no additional rock-placement along the pipeline length.
EXAMPLE: PIPELINES
Side-scan sonar images showing evidence of exposure on the pipelines resulting from the mobile seabed
EXAMPLE: PIPELINES
An overall value was established by totalling the normalised/ weighted values for the assessments and comparing the totals.
Criteria/ sub-criteria Weighting
(percentage)
Feasibility/ Technical Feasibility 7.5
Feasibility/ Risk of Major Project Failure 7.5
Safety 30
Environmental/ Environmental Risk 15
Environmental/ Energy Usage 5
Environmental/ Emissions 5
Societal/ Socioeconomic Risk 10
Cost 20
Total 100
Option Summed
Total*
Normalised/ weighted Score
5: Decommission in situ – Minimum Intervention 184 15.0
1: Full Removal – Reverse S-Lay/ Reel 194 14.2
2: Full Removal – Cut and Lift 194 14.2
3: Partial Removal – Cut and Lift 226 12.2
4: Decommission in situ – Minor Intervention 332 8.3
Weightings used in scoring
EXAMPLE: PIPELINES
0
5
10
15
20
25
30
No
rmal
ise
d/
We
igh
ted
Val
ue
Criteria/ Sub-criteria
Option 5: Decommission in situ - Minimum Intervention
Cost (20)
Societal (10)
Emissions (5)
Energy Usage (5)
Environmental Risk (15)
Safety (30)
Risk to Project Failure (7.5)
Feasibility (7.5)
0
5
10
15
20
25
30
No
rmal
ize
d/
We
igh
ted
Val
ue
Criteria/ Sub-criteria
Option 2: Full removal - Cut and Lift
Cost (20)
Societal (10)
Emissions (5)
Energy Usage (5)
Environmental Risk (15)
Safety (30)
Risk to Project Failure(7.5)
Cut and Lift: • Lowest scoring (45.5/ 100) option • Due to poor performance against
Cost, Safety and Energy and Emissions
• Maximum scores for Technical Feasibility and Societal Impacts
Minimum Intervention: • Scored highest (96.8/ 100) • Strong performance against
Safety, Environment and Cost
Problems occur because either evaluation criteria or options are:
• ‘Soft’ criteria that require judgements (typically where data is not available)
• Criteria described inadequately, leading to inconsistent use and interpretation
• Criteria that do not differentiate the options and are irrelevant to the decision being made
• Focusing on the method rather than the outcomes and consequences of the different options
• Overcomplicating the assessment, including too many or irrelevant options
• Inadequate technical knowledge of the options and their differentiators
RECOMMENDATIONS AND CONCLUSIONS
• The figure on right represents a summary of the method: Narrative + Scoring + Weighting
• Operators may wish to take an incremental approach to CA and start with the most simple and qualitative approach, moving only to the more complex and quantitative methods if it is judged necessary.
Source: Oil and Gas UK, 2015
For additional information on CA: [email protected] or [email protected] Copies of this presentation available at: www.bmtcordah.com
Thank you for your attention
