Reservoir In-Depth Waterflood Conformance: An Offshore Pilot Implementation

Abstract

Abstract Ebano field is a high permeability slope-channel turbidite reservoir located offshore Equatorial Guinea, West Africa. Oil production from this field started in May 2009 and water injection began in July 2009. Currently, the field operates with two wells; one injector and one producer with a well spacing of 1.5 km. Water breakthrough was observed approximately one year after water injection began, which was much earlier than the original prediction suggesting presence of water injection thief zone(s). Several reservoir management strategies to improve sweep efficiency were considered for implementation in this field including a reservoir in-depth waterflood conformance technology using a thermally active polymer (TAP). This paper will summarize the TAP pilot design, implementation, and performance interpretation based on a comprehensive surveillance program. The paper will also describe the workflow utilized to evaluate the technical feasibility of TAP technology (supported by detailed engineering, laboratory, and simulation studies). Engineering and laboratory studies to evaluate the technical feasibility of TAP started September 2010 and TAP pilot implementation commenced April 2011. Injection of TAP treatment was done from a barge requiring significant coordination between offshore and onshore to ensure safe handling and injection of chemicals. A total of 48,000 bbl of TAP were injected at an injection rate of 6,000 bbl/d, using a concentration of 15,000 ppm (4 cp injected). This treatment has been one of the largest offshore implementation using TAP technology. A detailed surveillance plan was put in place that included gathering and detailed analysis of injection/production data, injection pressure, produced water compositional analysis, production logs (PLT), and Fall-Off Tests (FOT) before and after the TAP treatment. Ebano pilot results validated TAP displacement and activation away from the injector. PLT data showed that the injection profile remained unaltered post treatment. Time-lapse FOT proved to be very useful in monitoring TAP performance. Uncertainties relating to how far away from the injector TAP was fully activated, injection pressure response (simulation vs. field), and production performance will also be addressed.