Abstract
Aqueous surfactant-nanoparticle mixtures have received great attention recently for promoting a more sustainable and efficient enhanced oil recovery (EOR) process. However, colloidal stability under reservoir conditions is considered a great challenge. In addition, the way synergy operates in EOR is not clearly understood. This study aims to formulate a cost-effective surfactant-nanoparticle mixture in a formation brine for efficient EOR in calcite-rich oil reservoirs. For this, bare silica nanoparticles were covalently grafted using an epoxysilane and blended with two commercial surfactants, namely a zwitterionic alkyl hydroxysultaine (AHS) and a binary zwitterionic-nonionic (ZN) surfactant, for both additional steric stabilization and EOR. The effects of additives alone or their mixtures were examined at solid-fluid and fluid-fluid interfaces to explore their impact on EOR. The surfactant-nanoparticle blend often showed a pH-responsive behavior at solid-fluid and fluid-fluid interfaces with particles serving as carriers or surface activity improvers for surfactant resulting in different extents of rock wettability alteration and emulsification. In oil recovery tests, optimum surfactant concentrations were found to significantly increase crude oil recovery of formation brine by 36 ± 1% original oil in place (OOIP) in secondary spontaneous imbibition which was further enhanced by 14 ± 0.5% OOIP upon adding a low particle concentration (0.01 wt %). The surfactant-nanoparticle formulation was also efficient in producing residual crude oil in tertiary mode (6% OOIP additional oil recovery after formation brine). The oil recovery results disclosed a high dependence on the emulsification ability of the blends with AHS-particle dispersions producing more stable emulsions and thus more crude oil compared to that of ZN.