Challenges, Lessons Learned, and Successful Implementations of Multilateral Completion Technology Offshore Abu Dhabi

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Summary Zakum Development Company (ZADCO), with the support from shareholders and the cooperation of Abu Dhabi Marine Operating Company (ADMA-OPCO), successfully completed the final design of the multilateral completion (MLC) system for Reservoirs A and B through the Multilateral Tie Back System (MLTBS) project. Well T-2 in the Upper Zakum field was recompleted as dual lateral/dual producer using a re-entry drilling system (RDS) Version 2 and a dual bore deflector (DBD) oriented and set on a latch coupling in the 7-in. liner hanger assembly. According to Technology Advancement Multilateral (TAML) level specification, the final MLC is categorized as TAML Level-4 E-2-PN-D/4-TR-SEP (Level-4, existing well application, two junction, producer with natural lift, dual completion, tubing reentry, separated flow). The multilateral liner hanger (MLLH) system (i.e., accommodating a latch coupling in 7-in. liner hanger assembly to have a certain access to the upper lateral) was the first successful application of that kind in the world. The teamwork and integrated approach for the trial planning and implementation, as well as lessons learned from a predesign trial (TAML Level-4 E-2-PN-D-TR-SEP using straddle assembly) for Well T-1 completed in 2000, have led to reaching the final goal of the MLC in Well T-2, which provides ZADCO with the following reservoir benefits: -Independent coiled tubing access to the upper (Reservoir A) and lower laterals (Reservoir B) through a dual completion to perform effective stimulation and reservoir monitoring.-Full bore access to each lateral immediately after pulling out the completion, which is an additional feature to the predesign of an MLC for Well T-1.-Allow selective water shutoff to cope with water breakthrough into the upper-cased lateral.-Possibility of extending well life by drilling a secondary lateral through a window joint installed in the upper-cased lateral. Moreover, another MLC trial, installed in the quadrant multilateral well RL-2 in 2005, has been successfully implemented by using mechanically selective through tubing re-entry equipment. This success was largely because of the lessons learned from a similar MLC design implemented in well RL-1 in 2001. These successful trial implementations proved the MLC system is applicable for any new/re-entry wells in ZADCO reservoirs, which provides new methods of reservoir management, and creates new completion strategies for ZADCO field development. This paper covers the MLC strategies, lessons learned through the successes and failures and the additional challenges planned for the future of the MLTBS project.