Abstract

Offshore China in the Cao Fei Dian 11-2 field (CFD 11-2), Bohai Bay, Joint Venture Partners Kerr-McGee China Petroleum Ltd (KMCPL) and China National Offshore Oil Corp. (CNOOC) were looking for original solutions to manage their water handling constraints. Downhole oil and water separation was investigated, with the goal of injecting most of the produced water downhole to alleviate surface processing requirements. This paper presents the completion design selected, results and equipment performance (to date), lessons learned and future applications.

Downhole separation is not a new idea. The technology has existed for many years, although most previous installations experienced issues which resulted in limited application of the technology. These issues are reviewed in detail because they were the driving force behind developing a new approach to overcome water handling constraints. To implement the technology at CFD 11-2, a candidate well had to be identified and a new SubSep completion designed. It used two independently controlled ESPs operating simultaneously to provide maximum control and flexibility. Chemical injection was incorporated to enhance separation efficiency using a fast-acting phase separation chemical. Monitoring systems were installed on both ESPs and at the downhole separator to survey all key parameters. A sample line was also included in the completion, and ported to the discharge stream of the hydrocyclone. This enabled real-time monitoring of oil ppm levels in the injected water, and facilitated timely optimization of ESP operating parameters and chemical performance.

The installation reduced the water-to-surface by 8,000 to 9,000 bwpd and achieved an oil carry over of 690 ppm, which was subsequently optimized to less than 300 ppm. The reduced water-volume-to-surface relieved process system pressure and provided an opportunity to increase production from other wells, delivering potential incremental production of up to 500 bopd.

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