Downhole Mechanical Isolation Equipment - Analysis of retrieval operations
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To encounter challenges when retrieving downhole mechanical isolation (DMI) equipment like plugs, junk baskets and prongs, using well intervention techniques, are not uncommon. These deviations result in additional runs, extra time and cost, and can - in the worst case - lead to failed operations. Up to now, these problematic retrieval operations have not been analysed in much detail. This thesis identifies the extent, consequences and nature of the challenges related to problematic retrieval operations of DMI equipment using intervention techniques. A comprehensive database of experience with retrieving DMI equipment based on the Statoil s drilling and well operations reporting system (DBR) was compiled. In total 244 retrieval operations from licenses on the Norwegian continental shelf, including all 2014 operations, were structured and compared. Key parameters such as well environment, DMI equipment type, installation method, retrieval method, well history and, well type have been systemised and analysed. In 40 of the 244 reviewed operations Statoil were not able to retrieve the DMI equipment on the first attempt, and had to use additional runs. The severity and nature of these problematic retrieval operations varied a lot, however led to in total 116 days of non-productive time. The analysis of the compiled database identified several factors that had negative effect on the outcome of the retrieval operations. In particular debris and the setting depth of DMI equipment had an evident effect on operational outcome. A solution to the debris related problems is to implement qualification for DMI equipment to fully function in unclean wells. This provokes the vendors to create more robust equipment against debris. This thesis recommends expanding the database of retrieval of DMI equipment, making it possible to apply a more thorough analysis of the various problematic retrieval operations and to open for a better benchmarking than today. Further, it is recommended to conduct a more extensive study on debris as a separate issue. The goal for such a study should be to understand both how debris occurs and to improve the practices for anticipating the debris. In addition, the study should figure out how to prevent and better deal with the challenges.