Lessons Learned in Drilling and Completing World Record Length Wells in a Giant Middle Eastern Carbonate Reservoir

Abstract This paper presents the challenges and lessons learnt in drilling and completing record length wells exceeding 50,000 ft total measured depth. Several new methods and technologies were required to successfully drill and complete these wells in a giant carbonate reservoir. The wells were drilled from an offshore island and the ability to reach reservoir targets far away from the island defers the cost of building a new island for reservoir development and results in significant cost savings. The wells are completed with limited entry liner in the reservoir section for optimized stimulation and production. An ultra-extended reach drilling program was created to deep dive into challenges faced in drilling and completing these 50,000+ ft wells. The program focused on managing drilling torque, equivalent circulating density (ECD), hole friction factors and telemetry in these ERD wells. The long lateral lengths (35,000 ft+) coupled with reservoir pressure variations exacerbate differential sticking and buckling risks making it difficult to deploy the 6-5/8" liner in a single run. To combat these challenges, mud density was optimized based on formation pressure measurements to reduce overbalance across the liner. Further, a tapered liner design was implemented to reduce the buckling risk. An extensive torque and drag study was conducted to optimize the liner and running string design. A downhole high frequency measurement memory tool was included in the liner running string to understand tension/compression loads while running and the data was used to update the liner design and operational procedures. These wells were successfully drilled to 50,000ft+ where heightened focus on well surveillance practices allowed for real-time optimizations. The team leveraged downhole sensors to maximize weight on bit (WOB) transfer in efforts to reduce buckling of the string and utilized previous well learnings to minimize the drag forces in the well. Ultra-ERD hole cleaning practices were applied in preparation for lower completion liner running operations. A dual tapered 6-5/8"x5-1/2" liner design was implemented and was successfully run to TD. The length of each size of liner was optimized based on the torque and drag study. The liner running string was upgraded from regular drill pipe to a full string of heavy weight drill pipe to reduce buckling risk and to maintain sufficient weight to run the liner. To reduce surge pressure while running the liner, an open-ended shoe was used in the liner. In addition to the above changes, operational practices were changed based on surveillance. For example, the circulation frequency to condition the aged mud, and removing the pipe stretch prior to running in hole on each double/stand, had to be implemented based on the hook load measurements and breakover loads observed during the run. The data recorded by the downhole memory tool validated the outcomes of the changes implemented and improved overall understanding of the string dynamics and hydraulic pressure impacts during the run.