Results of the UK Captain Field Interwell EOR Pilot

Abstract

Abstract An enhanced oil recovery (EOR) pilot was conducted by Chevron North Sea Limited ("Chevron") at the Captain Field in the UK North Sea between 2011 and 2013. Results from the polymer injection are presented along with an assessment of incremental oil recovery. The polymer solution was selected and qualified using a combination of laboratory and yard tests to determine optimum specifications for injection. The selected polymer was initially tested in an injectivity test in 2010, followed by continuous polymer injection in 2011, after establishing a waterflood baseline. Continuous polymer injection was terminated in 2013 due to injectivity decline associated with polymer emulsion injection. An unambiguous response from the reservoir was observed with a significant uplift in oil production. The three mechanisms of a successful polymer flood were observed and evaluated: (1) acceleration of oil production, (2) incremental oil production due to improved polymer sweep, and (3) water production and injection minimization. Our results demonstrate that waterflood recovery can be accelerated by polymer flooding. Secondly, incremental oil was produced due to increased volumetric sweep by changing the displacing phase fluid mobility with the viscosified polymer. Finally, the reduction in water production translates into reduced water handling and thereby lower operating costs. Before and during the pilot chemical injection, production logging tools were run in the injector and producer to measure their respective outflow and inflow phase profiles along the horizontal completions. These logs confirmed that polymer promotes crossflow to make injection rates more uniform along the wellbore. We also drilled a post-polymer observation well in the swept zone between the pilot wells. Logs from this well established remaining oil saturations to polymer that we used to confirm our calculations for polymer flood volumetric sweep. The post-polymer flood oil saturations confirmed the performance of the polymer flood. We show a full suite of surveillance data and its use in quantitative interpretation. We also show innovative uses of the surveillance data in our interpretation methods. The results prove the subsurface and operational success of polymer flooding a heavy oil reservoir with horizontal wells, even in a harsh offshore environment such as the UK North Sea.