Recovering oil from carbonate reservoirs by waterflooding is often ineffective due to the combination of ineffective sweep and the originally oil-wet nature of that rocks. Ionic liquid monomers and polymers have recently attracted attention as chemical agents for enhanced oil recovery. 2-acrylamido-2- methylpropane sulfonic acid copolymer with methacrylic acid (AMPSA/MAA) diluted in sea water at 3000 ppm was previously screened among other polyionic liquids (PILs) at different concentrations (Abdullah et. al, 2017) and proved to be the most effective enhanced oil recovery chemical. The PIL AMPSA/MAA was tested with sandstone and proved efficient on enhancing oil recovery. In this study, we extend the work to explore the efficiency of such PIL on carbonates.

A post-secondary water flooding was conducted and an incremental tertiary recovery of 6% original oil in place (OOIP) corresponding to 12% residual oil in place (ROIP) was obtained indicating the efficiency of the AMPSA/MAA PIL. This carbonate recovery compares to 10% OOIP in sandstone as reported in previous study (Abdullah et. al, 2017). This difference can be attributed to the low permeability characterizing the carbonate sample used in this work in comparison to the sandstone tested earlier. Seawater-crude oil Interfacial tension and contact angle measurements on carbonate substrate were performed at elevated temperature and pressure to investigate the possible recovery mechanisms. Interfacial tension (IFT) resulted in insignificant IFT drop. On the other hand, contact angle measurements confirmed wettability alteration towards more water wet state indicating it as the main recovery mechanism in carbonates.

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