A core-scale study of polymer retention in carbonates at different wettability and residual oil conditions

Abstract

As an effective technique to improve oil recovery, polymer flooding has been successfully used worldwide in many fields. The retention of polymer in reservoir increases the project cost, retards polymer transport, and thus delays the incremental oil response. Therefore, low polymer retention is crucial for a successful polymer-flooding project. Accurate quantification of this parameter is accordingly essential. Polymer retention is often evaluated in the absence of oil, which is not representative of the polymer-flooded oil regions in the reservoir. There is also a lack of consensus on the wettability impact on retention in the literature. In this work, the polymer retention in carbonates is investigated at varied wettability conditions, in the presence of oil as well as in the absence of oil. A sulfonated polyacrylamide polymer is evaluated in this study, and representative reservoir fluids and core samples are used in the experiments. The results demonstrate that the studied polymer exhibits relatively low retention in the carbonate cores, ranging from 20.9 to 60.8 μg/g-rock. The inaccessible pore volume (IPV) ranges from 9.0 to 12.0% pore volume (PV). These results demonstrate a potential of this polymer for carbonate reservoir applications. More importantly, the results indicate that the polymer retention is reduced more than 50% in the presence of residual oil. In other words, the presence of oil in actual reservoir condition has a positive side in terms of polymer consumption. Accordingly, it is a factor that must be either simulated or accounted for. On the other hand, the results suggest that the wettability impact on polymer retention is small compared to the presence of oil. Furthermore, both residual oil and wettability have insignificant impact on polymer IPV. In summary, the polymer retention results from single phase displacement experiments tend to be more conservative. When using these retention estimates for designing a polymer flooding project, their conservative nature should be kept in mind or factored in.