A study of Residual Oil and Wettability Effects on Polymer Retention

Abstract

Summary The propagation rate of polymer solution through reservoir rock is significantly affected by the magnitude of polymer retention, and consequently, impacting oil recovery and chemical consumption. Therefore polymer retention is a critical parameter for both the numerical prediction and the actual performance of a polymer flood. A clear understanding of the magnitude and influencing factors is still desired for polymer flooding in carbonates. In this study, we investigate the retention of a sulfonated polyacrylamide polymer in carbonate cores. The impacts of residual oil and wettability on polymer retention are studied by performing coreflooding experiments at reservoir conditions. Representative reservoir fluids and core samples are used for both experiments of single phase displacement and in the presence of residual oil. Two slugs of polymer with KI tracer are injected, and effluent polymer and tracer concentrations are analyzed for determining polymer retentions and inaccessible pore volumes (IPV). Results show that the retention of the tested polymer in carbonate cores is relatively low, ranging from 26.0 to 60.8 µg/g-rock. In the presence of residual oil the polymer retention has more than 50% reduction. This indicates that the oil in reservoir environment has positive impact on polymer consumption, and the studied polymer has a potential for carbonate reservoir applications. Compared to the significant effect of the oil presence, it was observed that wettability change caused a slight variation in polymer retention results. This suggests that wettability has small impact on polymer retention estimates. Furthermore, the polymer IPV results obtained in the presence and in the absence of oil are very close, ranging from 11.0% to 12.0% of pore volume (PV). This indicates that the presence of oil has insignificant effect on polymer IPV. This study shows that evaluating polymer retention using single phase displacement experiment tends to give an overestimated result, which may lead to a conservative estimate in polymer consumption.