Insights into Hybrid Smart Water Assisted Foam (SWAF) Flooding in Carbonate Reservoirs: A Combined Numerical and Experimental Approach

Abstract

Abstract Smart Water Assisted Foam (SWAF) flooding is a promising and an emerging synergic enhanced oil recovery (EOR) technique that combines smart water and foam injections. This technique works best in carbonates with mixed-to-oil wet wettability, where smart water (SW) alters the rock wettability towards a water-wetting state and stabilizes the foam lamellae, and surfactant aqueous solution (SAS) reduces interfacial tension (IFT) leading to improvement in oil recovery. This paper provides more insight and better understanding of the controlling mechanisms behind incremental oil recovery by this hybrid technique through a combined numerical and experimental approach. In this study, a mechanistic approach using surface complexation modeling (SCM) and DLVO theory was followed for modeling this hybrid technique, which aids in a better understanding of crude oil/brine/rock (COBR-system) interactions. The SCM considered the SAS-rock and SAS-oil interactions, which enabled improved prediction of rock wettability alteration through capturing surface complexes and surface potentials in the COBR-system. The Phreeqc simulator was used and the simulations were performed at 80°C. The proposed SCM was validated against experimentally measured contact angle and zeta potential measurements. Subsequently, to identify the best SAS formulations that promote stable foam generation and its propagation inside porous media during coreflood, foamability and foam stability tests were performed. Successful combination of SAS and Gas (i.e., SAG) candidates were confirmed by conducting coreflooding tests. Furthermore, the CMG-STARS simulator was used to history match a coreflooding experiment with providing insights into the relative permeability curves and the related interpolation parameters. Based on the numerical and experimental results, a stable water film was noted for low salinity case of MgCl2 solution where the same surface potential signs were obtained for both rock-brine and brine-oil interfaces. Also, the maximum contact angle reduction for the single ionic compounds was demonstrated by MgCl2 (i.e., 3500 ppm), which was 6.7°. Further, the most effective SAS was the MgCl2 + CTAB + AOS (i.e., 3500 ppm) solution. Moreover, the best foam was generated via MgCl2 + CTAB + AOS + N2 (i.e., 3500 ppm). Thereafter, the SWAF process yielded an incremental oil recovery of 42% of oil initially in place (OIIP), resulting in a cumulative oil recovery of 92% OIIP. Subsequently, utilizing the CMG-STARS simulator, the experimental coreflood was accurately history matched using the validated SWAF proposed model with a satisfactory error of only 6.7%. Under optimum conditions, it is anticipated that the newly proposed hybrid SWAF EOR-technique is more appealing from an economic and environmental standpoints. This work presents a workflow to mechanistically and experimentally determine the optimum conditions for the SWAF process in carbonates. The study also sheds insight into the mechanisms controlling the SWAF method and promotes designing successful field-scale pilots in carbonate reservoirs.