Summary
Engineered water injection (EWI) has gained popularity as an effective technique for enhancing oil recovery. Surfactant flooding is also a well-established chemical enhanced-oil-recovery (EOR) technique in the petroleum industry. The hybrid surfactant flooding/EWI (surfactant/EWI) technique has been studied experimentally and showed promising results. However, there are very limited numerical applications on the hybrid surfactant/EWI technique in carbonates in the literature. Also, the studies applied under harsh conditions of high temperature and high salinity are even fewer. In this study, a numerical-simulation model is developed and used to investigate the hybrid effect of surfactant/EWI in carbonates under harsh conditions. This developed model was validated by history matching a recently conducted surfactant coreflood in the secondary mode of injection. Oil recovery, pressure drop, and surfactant-concentration data were used. The surfactant-flooding model was then coupled with a geochemical model that captures different reactions involved during EWI. The geochemical reactions considered include aqueous, dissolution/precipitation, and ion-exchange reactions. The proposed model has been further validated by history matching another experimental data set. Furthermore, different simulation scenarios were considered, including waterflooding, surfactant flooding, EWI, and the hybrid surfactant/EWI technique.
For the case of EWI, wettability alteration was considered as the main mechanism underlying incremental oil recovery. However, both wettability alteration and interfacial-tension (IFT) reduction mechanisms were considered for surfactant flooding depending on the type of surfactant used. The results showed that for the hybrid surfactant/EWI, wettability alteration is considered as the controlling mechanism where surfactant boosts oil-recovery rate through increasing oil relative permeability while EWI reduces residual oil. Moreover, the simulation runs showed that the hybrid surfactant/EWI is a promising technique for enhancing oil recovery from carbonates under harsh conditions. Also, hybrid surfactant/EWI results in a more water-wetting rock condition compared with that of EWI alone, which leads to lower injectivity, and hence, lower rate of propagation for ion-concentration waves. The hybrid surfactant/EWI outperformed other injection techniques followed by EWI, then surfactant flooding, and finally waterflooding. This work gives more insight into the application of hybrid surfactant/EWI on enhancing oil recovery from carbonates. The novelty is further highlighted through applying the hybrid surfactant/EWI technique under harsh conditions. In addition, the findings of this study can help in better understanding the mechanism behind enhancing oil recovery using the hybrid surfactant/EWI technique and the important parameters needed to model its effect on oil recovery.