Synergistic Surfactant Blends for Wettability Alteration in Wolfcamp and Eagle Ford Shale for Improved Oil Recovery

Abstract The goal of this work is to develop synergistic surfactant blends that can perform wettability alteration for improved oil recovery (IOR) in tight liquid-rich unconventional shale reservoirs. Shales samples from Eagle Ford and Wolfcamp formation were used in this study. The performance of these surfactant systems in altering the wettability and improving the spontaneous imbibition process was evaluated. Comprehensive screening of surfactants (anionic, non-ionic, zwitterionic) was performed in this study. First, aqueous stability tests of these surfactant systems were performed at reservoir temperature. Second, contact angle experiments were conducted on polished oil-wet shale (Eagle Ford and Wolfcamp) chips to screen formulations with optimal wettability-altering capabilities. Third, bulk emulsion stability was investigated by measuring the half-lives of the emulsions. Fourth, the interfacial tensions between oil-surfactant formulations were measured via the pendant drop method using a goniometer. Finally, spontaneous imbibition experiments in tight cores such as carbonates and shale were performed to evaluate the efficacy of these formulations in recovering oil. Several anionic surfactants and their blends with anionic, non-ionic, and zwitterionic cosurfactants were shortlisted based on the aqueous stability tests. Polished shale chips from Eagle Ford and Wolfcamp formation were made oil-wet by aging them with crude oil at 85 °C for 30 days. Contact angle experiments revealed that these synergistic surfactant blends can alter the wettability from oil-wet to water-wet conditions and outperform the performance of the individual surfactant system. The spontaneous imbibition experiments demonstrate that a significant amount of oil (11.8 to 52 % OOIP) can be recovered from tight carbonate rocks by optimally selecting surfactant formulations. It was shown that surfactant imbibition in an originally oil-wet shale sample can recover a significant amount of oil (12.96 to 22.4% OOIP). Unconventional liquid-rich shale plays such as Eagle Ford, Bakken and Wolfcamp constitute a major portion of the oil production in the US. Surfactants can significantly improve production from such shales and improve oil recovery. This study offers a novel systematic investigation of synergistic surfactant blends which alters the wettability of oil-wet shale to water-wet and induce spontaneous imbibition in liquid-rich shales to increase oil recovery.