Alternative Methods for Tubing Removal
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When the production from a well is no longer profitable, the options are to either permanently plug and abandon (P&A) the well, or to re-use the slot by plugging the original well and sidetrack a new wellbore (slot recovery). The purpose of P&A is to establish permanent barriers to prevent migration of hydrocarbons to the surface, in a safe and cost-effective manner. In the coming years, there is an expectation of a significant increase in subsea wells needed to be plugged and abandon. With today s time consuming and expensive P&A operations, the industry desire new innovative methods able to reduce time and cost. The industry has today a large focus on technology that enables performing the plug and abandonment operation by light intervention vessels. In order for that to occur solving key challenges, such as tubing removal is required. The established approach to remove the tubing in subsea wells today is to use a semi-submersible drilling rig. The main objective for this project has been to investigate alternative methods for tubing removal. After an evaluation, the most promising alternative was the alternative method, tubing expansion with axial cuts. The method works by bisecting the tubing between the tubing couplings, axial cut one part, expand it and then pull the tubing parts together. Based on 12 m length between the couplings the method is able to create 5.5 m window per operation. Performing the operation 6 times creates a window greater than 30 m and thus fulfilling NORSOK D-10 minimum requirements for logged cement. If the logging shows acceptable cement bonding, the secondary plug can be set. To evaluate whether one, two or four axial cuts are optimal, An FE-analysis was carried out. Results from the analysis suggested two axial cuts with pressure applied by a mechanical tool only to the region around the cut are optimal. The operational steps and tools necessary to perform the operation have been assessed. By using a single-trip tool, it was estimated that the method would take approximately 21 hours to complete and be economically feasible for well lengths above 1445 m when the alternative is to pull with a semi-submersible drilling rig. Further work should be investigating the possibility of decreasing the axial cutting operation time. One option is to use two cutters simultaneously. Further, laboratory testing to confirm the FE-analysis and the expansion tool design should be carried out.