Experimental investigation of dynamic interfacial interactions at reservoir conditions

Abstract

Much of the research on wettability in the existing literature has been done using stocktank oils and at ambient conditions. The main objective of this study is therefore to examine the validity of ambient measurements in inferring in-situ reservoir wettability. For this purpose, Drop-Shape-Analysis for interfacial tension and Dual-Drop-Dual-Crystal (DDDC) contact angle measurements have been carried out using dolomite rock, Yates reservoir stocktank and live crude oils and Yates synthetic brine at Yates reservoir conditions of 82oF and 700 psi. Two types of surfactants (nonionic and anionic) in varying concentrations have been used to study the effect of surfactants on wettability alteration in Yates reservoir. Dynamic behavior of interfacial tension (IFT) of crude oil - brine are mainly caused by the polar components or surfactants in the liquids. The oil composition especially light ends, and brine composition also have effect on it. A four-staged model was adapted from the literature to explain this time-dependent behavior of IFT. An advancing contact angle of 156o measured for dolomite rock, Yates stocktank oil and Yates synthetic brine in the absence of surfactants showed the strongly oil-wet nature. Experiments with Yates live crude oil at reservoir conditions indicated weakly water-wet behavior with a water-advancing angle of 55o For oil-wet stocktank oil system, the anionic surfactant was able to alter wettability from strongly oil-wet (156o) to less oil-wet (135o). No significant wettability alterations were observed with the nonionic surfactant in the stocktank oil containing system. However, for water-wet live oil system, the nonionic surfactant injection altered the wettability to intermediate-wet and the anionic surfactant altered it into strong oil-wet. The oil-wet behavior observed with Yates live oil due to anionic surfactant indicates the ability to this surfactant to form continuous oil-wet paths for mixed-wettability development. These experiments clearly indicate the need to use live crude oils at reservoir conditions for in-situ reservoir wettability determination. Furthermore, these experiments provided clear evidence that the surfactants used altered wettability to either intermediate-wet or mixed-wet, which could result in potential oil recovery enhancements in field applications.