Sustained casing pressure (SCP) in oil and gas wells can result in leakage to the seabed if not properly checked during the final phase of the well life cycle. The escape of well fluid to the seabed as a result of SCP can lead to significant environmental damage, if not properly managed by the operator.A recently developed innovative technology can drastically reduce the cost of sustained casing pressure mitigation during well plug and abandonment (P&A). The non-removal of the inner casing string before potential SCP sections are milled translates into savings for the operator. This specialty tool is designed to go through riser restrictions and pass through restrictions in the production casing internal diameter to mill the sustained casing pressure section in the intermediate casing. The mitigation of SCP in a single annulus is a challenging operation. In some cases, SCP exists in multiple annuli and can be more challenging because the removal of steel from the well is an expensive operation. The high-expansion section mill has been deployed in combination with improved milling technology in offshore well abandonment and has lowered the cost of well P&A.The catastrophic impact of losing well barrier elements as a result of sustained casing pressure migration must be prevented. The cost of achieving this in some cases can be more than the cost of constructing a new wellbore. Moving forward, the industry will benefit from this technology by having the ability to mill a casing string section within a section. This capability eliminates the existing practice of performing several cut-and-pull attempts and/or casing milling, followed by a section milling operation. Objective/ScopePressure generated within an annulus by thermal expansion of wellbore fluid during production is called annular pressure buildup (APB). APB can be bled off in platform and land wells, and it does not rebuild afterwards.The objective of this paper however is to address the challenges of sustained casing pressure (SCP) in well abandonment occurring from the rebuilding of casing annulus pressure after bleedoff. Sustained casing pressure is not caused solely by temperature fluctuations or pressure introduced in the well by the operator. Subsea wells have no penetration through the high-pressure wellhead housing for annuli B, C, D and other annuli that may exist in the well. The casing shoes are left open and can serve as a pathway for SCP in the casing annuli. The open casing shoe mitigates the annular pressure buildup due to
The operator, rig contractor and services company formed a trilateral collaboration to plan the safe plug and abandonment of four onshore wells located in a densely populated region of Indonesia. These wells, located in scattered locations, posed a significant logistical challenge for project mobilization and moves between the wells. Well information was incomplete due to a change in asset ownership. Some of the challenges faced in these wells were: Well integrity issues resulting from the presence of H2S and CO2Sustained casing pressureSurface water safetyFluid losses Personnel safety and future well integrity was crucial to this operation. Consequently, plans were developed to conduct the operation safely and efficiently, as well as to provide solutions that mitigated well integrity challenges. The method adopted for this project was to approach this as an integrated project where the collaboration team was responsible for planning, executing, monitoring and closing out all segments of the project. Well information from the previous field operator was analyzed and a solution to safely plug and abandon these wells was created. Because inadequate well information posed a major challenge, the collaboration team planned multiple contingencies. An abandon-the well-on-paper (AWOP) workshop was organized to review and refine the execution plan. An intelligent coiled tubing system, which could be used for simultaneous logging and pumping operations, was selected as well as an efficient and environmentally friendly mechanical pipe cutter that did not use explosives or hazardous chemical substances for tubing severance operations. The sustained casing pressure challenges (in previously fully cemented/non sealing annuli) were addressed by using advanced milling technology for section milling. The early engagement plan enabled development of a project execution strategy that clearly outlined equipment mobilization schedules from various locations in Indonesia. Because of the collaborative projects structure, local personnel recruited for this project were quickly on boarded and integrated with the rest of the project team. This approach led to the safe and efficient execution of the plug-and-abandonment scope of work, with zero HS&E incidents and 167 perfect HS&E days during project execution. Extensive testing of cement mix water was introduced to this project. The testing improved the cement design and enabled accurate plan transition times that reduced waiting on cement. Based on lessons learnt from the first well, extensive logging operations were performed to determine the formation temperature and specific leak locations in the casing. These pre-cementing logging operations helped in collecting accurate well temperature and pressure information that aided the design of cement recipes for the barriers placed in these wells.
Well log analysis is one of the methods for reservoir characterization, in the oil and gas industry. Logs are used for subsurface formation evaluation. They are useful in hydrocarbon zone identification and volume calculation. Interpretation of well log involves sequential steps, which are lithology, shale volume, porosity and saturation determination. It is unwise to analyze well log without following the logical steps, as this could introduce errors in the result. Petrophysical and Geomechanical properties are two classes of properties for reservoir characterization. The computed volume of shale in the reservoir was 10%, the average water saturation was 30%, and the average porosity was 25pu. The bulk density decreased from 2.15g/cc to 1.95g/cc and there is a considerably lower acoustic impedance in the hydrocarbon bearing sands. In challenging reservoirs, where traditional petrophysical methods do not give definitive results, the use of geomechanical methods will improve interpretation certainty and help to clear doubts in the interpreted results.
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