Summary Polymer flooding has matured into a commercially viable enhanced oil recovery (EOR) method. Yet, substantial volumes of oil often remain trapped post-polymer injection, and economically feasible solutions for further recovery are limited—with no widely reported successful field implementations to date. With this study, we present field results from alkali-polymer (AP) injection following long-term polymer flooding. In this approach, alkali reacts with reactive crude oil to generate in-situ soaps that mobilize residual oil, while polymers maintain sweep efficiency and enhance microscopic displacement. The oil exhibited a total acid number (TAN) of 2.14 mg/L, indicating its high chemical reactivity with alkali. Before field implementation, a comprehensive laboratory program was conducted to optimize alkali and polymer selection, concentrations, and rheological properties—while addressing interactions with reservoir rock, near-wellbore area effects, geomechanics, and reservoir architecture. Scale inhibition strategies and water quality controls were also developed to mitigate operational risks. Initial field pilot results indicate that AP injection using the selected alkali and polymer achieves additional oil recovery, even after previous polymer flooding. The simplified chemistry of alkali and polymer compared with more complex alkali/surfactant/polymer (ASP) formulations reduces surface facility complexity and operating expenditures (OPEX). It should be noted that for AP flooding to be effective, sufficient soaps must be produced through the reaction of alkali with oil, and these soaps should not be overly hydrophobic, as this would prevent achieving low interfacial tension (IFT). Scaling was prevented in injection wells using softened water and managed in producer wells through targeted inhibitor dosing. Economic evaluation reveals that AP injection post-polymer flooding can achieve unit technical costs below EUR 30/bbl, with further cost reduction and performance optimization possible through chemical and operational refinement. Additionally, direct AP injection—without preceding polymer flooding—shows promise for oil reservoirs containing reactive oils, potentially leading to higher net present value (NPV) through higher incremental oil recovery and accelerated revenue realization compared with AP after polymer flooding.
Clemens et al. (Sun,) studied this question.