Post-flooding with Associative Polymer/Alkali/Surfactant Ternary System After Polymer-Enhanced Oil Recovery

Abstract

Successful story has been witnessed on polymer flooding in Daqing oilfield, from which the average oil recovery factor in major reservoirs can reach 15% or even higher. However, some of reservoir blocks with polymer flooding have entered subsequent water flooding. Meanwhile, around 50% of the geological reserves still remained after polymer flooding, so that it is urgent to seek alternative solutions to further improve oil recovery after polymer flooding. While it is well recognized that alkali/surfactant/polymer (ASP) ternary system can not only reduce the oil–water interfacial tension, but also expand the sweep volume, higher traditional polymer concentration is needed to achieve ideal mobility control, resulting large injection quantity. To balance oil recovery efficiency and formulation cost, it is desirable to reduce dosage of polymer used. In this work, associative polymer (AP) was used instead of conventional partially hydrolyzed polyacrylamide (HPAM) to develop ASP ternary system. It is found that when compared with its alkali/surfactant/HPAM (ASHP) ternary system counterpart, the alkali/surfactant/AP (ASAP) ternary system shows better thickening ability and decreases the polymer dosage by more than 40%. In addition, the ASAP ternary system exhibits much higher resistance factor and residual resistance factor than the ASHP formulation, indicative of good profile control performance. The results of oil displacement using natural core reveal that the ASAP ternary system can increase oil recovery by more than 10%, 3% higher than the ASHP ternary system. Field trial based on the optimized laboratory ASAP ternary system formulation has obtained the stage recovery factor of 3.13% and the predicted final recovery factor of 7.76% after 0.615 pore volume of cumulative injection volume of ASAP slug.