The First Successful Deployment of Downhole Oil-Water Separation Technology in South China Sea: Lessons Learned and Way Ahead

Abstract

Abstract The operator of an offshore oilfield located in South China Sea, has been researching for efficient methods to tackle the production constraints from the increasing produced water amount and maximize oil recovery. An ESP assisted downhole oil and water separation system, known as SubSep system, was designed and successfully installed in year 2014. During the operations, the system achieved designed separation performance but went offline due to heavy sand problem. This paper concentrates on sharing the experience of complete cycle of system design, deployment, operation and post-job investigations, and discussing the lessons learned and future improvements for downhole oil and water separation technology. The downhole oil and water separation system features in two independent ESP to operate simultaneously: the lower ESP feeds well fluid into multistage hydrocyclone where oil is separated from water, and enters upper ESP to lift to ground, while water is injected to injection layer. Installed in year 2014, the system is the first successful deployment of downhole oil and water separation technology in South China Sea area. The system has totally operated 480 days, during which various operation methodologies were experimented and outcomes analyzed. In normal operation the separated water collected from sample line in water injection zone showed 99ppm oil, and 75% of water was reduced to ground, which signaled the significant success in water and oil separation. The system went offline when surface water rate increased abnormally and injected water with high oil concentration. Further investigation of pulled system showed clear evidence of abrasions from sand and quarts. Future improvement pathways were identified as applying multiple sand control methods, simplifying completion strings, enhancing chemical injection programs and implementing surface experiments. This paper shares the experience of a complete cycle of design, deployment, operation, and post-job investigations of a downhole oil and water separation system, and provide reference for future improvements and optimizations