Maintaining well integrity during slot recovery operations
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The temporary plug and abandonment (P&A) of old wells, and the following slot recovery, will be important for increasing the average rate of recovery from the Norwegian Continental Shelf (NCS). However, these operations faces challenges like high costs, safety concerns, environmental issues, and rapidly growing demand. Maintaining well integrity may be difficult when re-entering old wells. The demand for increased efficiency may lead operators to compromise on safety to finalize projects in time. This thesis tries to give a broad understanding of the well integrity issues on the NCS, and then tie these ndings around the term slot recovery operations. It will be important to understand the aspects which aects the lifetime of a well. Especially the long-term pressure, temperature and chemical effects on casings/tubings are important aspects to be understood. If this is done, one can increase the material lifetime in a well, and thus be able to re-use more of the casing strings in a slot recovery. These measures will help to keep marginal fields protable for a longer period. The thesis has also kept a strong focus on the challenges regarding the planning phase of a slot recovery operation. Of the essential factors in a slot recovery is to verify the old barrier envelope, and based on these findings create a robust operational plan. One of the mistakes which has been done in several slot recoveries is that the plan is created before any tests have been done. Once the plan is set and signed by the management, changes are harder to implement. Testing of the well often reveals unexpected factors which needs to be taken into consideration when planning an operation. Two separate slot recovery operations were also studied. They were carefully chosen to highlight typical issues with a slot recovery, and thus show that the theory fits with the reality. The requirements and guidelines for wells on the NCS also needs to be more customized for slot recovery operations.