FACTSHEET 2: WELL RE-USE

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Can oil & gas wells be re-used for CO2 injection?

An example of a CCS chain (Image: CO2DeepStore)

PurposeAs oil and gas fields come to the end of their lives and infrastructure is no longer required for its original use, what opportunity is there to re-use infrastructure for carbon dioxide transport and storage? This factsheet considers the potential for re-using oil and gas wells to inject CO2 as part of a carbon capture and storage (CCS) project.

Summary●● Given the technical difficulties, risks and economic realities, new wells are most likely to be required for CCS.

●● Due to the different design requirements for CO2 injection versus oil and gas production, most redundant wells are unsuitable for re-use.

●● The condition of redundant wells is often uncertain and would require considerable assessment and/or remedial intervention to enable re-use, which could be at a significant cost.

FACTSHEET 2: WELL RE-USE

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Potential opportunityIn theory, redundant oil and gas wells could be repurposed for CO2 injection, but there are technical, commercial and regulatory factors, which need to be considered, in assessing the potential for re-use. Fields and wells should be considered on a case-by-case basis. This factsheet provides a summary of the potential for re-use of redundant oil and gas wells and highlights some of the key factors, which must be considered.

General considerations●● As part of an overall system, the potential to re-use a well is only of interest if the depleted oil or gas field (or connected aquifer) is suitable for CO2 storage, if the offshore facilities to which the well is connected are suitable, and if there is a reasonable prospect of transporting CO2 to that location.

●● The suitability of the subsurface reservoir should be considered first and include considerations of:

●● capacity (is the reservoir an appropriate size for the project?) ●● integrity (can the CO2 be safely stored at this location?) and ●● injectivity (can the CO2 be injected at a rate which fits with the need?)

●● The age and condition of the well is likely to be a key factor in assessing its suitability. Old wells may have issues with corrosion or other integrity concerns.

Commercial considerationsAssuming that the location is suitable for CO2 storage, the key commercial considerations for well re-use are cost and risk. In theory, re-using an existing well should cost less than drilling a new one. The costs associated with the reuse of wells are highly dependent on the specificities of each well. The cost of reuse would include costs for assessment of wellbore, casing and completion integrity, as well as some remedial and conversion work. Repurposing an existing well may take 7 to 21 days; drilling a new well could take between 30 and 90 days, depending on depth and complexity.

However, as outlined in the technical section below, many redundant oil and gas wells will be unsuitable based on design issues. Those that could be considered suitable may carry a level of risk, which, given the potential consequences, may not be considered acceptable.

FACTSHEET 2: WELL RE-USE

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Technical considerations●● The basis of design for an oil and gas well is different to that for a CO2 injection well. The significant differences in operating criteria, such as temperatures, pressures and fluids in the well, mean that the various elements of the well, including the existing wellhead, casing strings and downhole equipment, are unlikely to be suitable for CO2 injection. This is due to pressure rating, metallurgy and elastomeric materials in equipment already in the well.

●● The optimum bottom-hole location for CO2 injection may be different than for oil and gas production. This may exclude the re-use of certain wells, or require sidetrack or well deepening activity. Sometimes the cost and uncertainty associated with re-entering an existing well is so great that a new well is preferred.

●● In certain circumstances it may be possible to re-use a well where either the design criteria are acceptable or remedial intervention could modify the well’s installed equipment to fit the required design criteria. This may involve more than a standard workover to replace tubing and completion equipment.

●● Re-use may involve obtaining additional information on the downhole condition of the well, such as casing corrosion and cement/casing bond integrity, or performing additional tests, such as pressure testing casing or wellhead, or performing injectivity tests.

Generic well schematic (Image: Pale Blue Dot)

FACTSHEET 2: WELL RE-USE

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Regulatory considerations The UK Oil and Gas Authority (OGA) has responsibility for managing all licence-related activity for both petroleum operations and CO2 storage. The licensee is not permitted to commence, suspend or recommence the drilling of any well without the consent of the OGA, or to complete, recomplete or abandon any well. The UK Health and Safety Executive require detailed notification of specific well operations, which must have been independently assessed by a well examiner. The Offshore Petroleum Regulator for Environment and Decommissioning (OPRED) within the Department for Business, Energy and Industrial Strategy (BEIS) regulates decommissioning of offshore oil and gas installations.

Well abandonment approval is provided by the OGA and would usually form part of the overall decommissioning programme, preparation of which is an obligation of the petroleum licence and approval of which is the responsibility of OPRED. Well re-use would also require consents from the agencies listed above, whilst recognising that the re-use of wells for CO2 injection would normally be part of a wider facilities re-use opportunity.

The transfer of assets between parties leaves an obligation on the previous party(ies) (Section 29 obligations under the Petroleum Act) to fund decommissioning if the new party fails to meet its obligations. After decommissioning, in the event of an issue, all parties who have held the licence are also liable (under Section 34 of the Petroleum Act) for addressing the matter.

The transfer of assets for a CO2 storage service, which are outside the terms of the petroleum licence, will require consent from the Secretary of State to release previous petroleum licence holders from their Section 29 and 34 accountabilities.

Cross section of the Hamilton depleted gas field, East Irish Sea (Image: Pale Blue Dot)