Measurement of Surfactant-Induced Interfacial Interactions at Reservoir Conditions

Abstract

Summary The effect of surface-active chemicals on oil/water interfacial tension (IFT) and wettability in crude-oil/brine/rock systems at reservoir conditions is important in enhanced-oil-recovery (EOR) processes. However, most of the experimental studies on IFT and contact angles have been conducted at ambient conditions and using stock-tank crude oils. In this study, live and stock-tank crude oils have been used at reservoir conditions to make IFT and dynamic contact-angle measurements using the drop-shape-analysis (DSA) and dual-drop/dual-crystal (DD/DC) techniques, respectively. Yates reservoir rock and fluids, and two types of surfactants (nonionic and anionic) in varying concentrations have been used at reservoir conditions of 82°F and 700 psi (27.8°C and 4.8 MPa). The dynamic oil/water IFT was found to be a strong function of oil composition and of temperature, and it showed a slight dependence on pressure. An attempt has been made to explain the dynamic behavior of IFT using a four-stage mechanistic model involving induction, diffusion, kinetic-barrier, and equilibrium stages. The significant difference observed between the advancing contact angles of live oil (55°) and stock-tank oil (154°) clearly indicates the need to use live oils at reservoir conditions to determine in-situ reservoir wettability. Anionic surfactant altered the weakly water-wet behavior of live oil to strongly oil-wet (165°). It was also able to alter the strong oil-wet behavior of stock-tank oil to less oil-wet (<135°). The nonionic surfactant was able to alter the water-wet live oil system to intermediate-wet (82°), while it did not affect the strongly oil-wet behavior of stock tank oil system. The oil-wet behavior observed for live oil with surfactants indicates the capability of these surfactants to develop continuous oil-wet paths for potential mixed-wettability development. Thus, this study is of practical significance in cases where the surfactant-induced wettability alterations to either intermediate-wet or mixed-wet can result in improved oil recovery through the lowering of both capillary and adhesion forces.