Experimental Study of Spreading and Wettability Effects by Surfactants in Condensate Reservoirs at Reservoir Conditions

Abstract

Abstract Gas condensate reservoirs suffer a rapid decline in productivity as the flowing bottom-hole pressure falls below the dew point. This reduction is caused by condensate accumulation near the wellbore. This study aims to perform an experimental investigation into potential remedies through chemical treatments to modify the fluid-fluid spreading coefficient and wettability in condensate buildup regions to enhance condensate recovery and gas productivity. In this study, experiments were conducted at reservoir conditions of 2264 psia and 210 °F by using representative condensate reservoir fluids. Spreading coefficients were determined through measurements of oil-water, water-gas and gas-oil interfacial tensions using the Drop Shape Analysis (DSA) and capillary rise techniques. Dynamic contact angles were measured using the Dual-Drop-Dual-Crystal (DDDC) technique to characterize reservoir wettability. An advancing angle of 153° obtained from the experiments indicated that this representative sandstone condensate reservoir had a strongly oil-wet nature at reservoir conditions. In order to examine the capability of certain chemicals to alter spreading and wettability behavior at reservoir conditions, an anionic surfactant was screened for use in the experiments at the concentration levels of 500, 1500, and 3000 ppm. Although spreading coefficients were all positive for the gas-condensate-brine (with and without surfactants) systems, a decreasing trend was observed in the systems after the surfactant application. This indicates that condensate recovery is still enhanced from surfactants usage in this strongly oil-wet system. The low concentration 500 ppm of anionic surfactant was not found to change this sandstone reservoir wettability at reservoir conditions, however, the wettability alteration from strongly oil-wet to weakly oil-wet or intermediate-wet was observed as the surfactant concentrations increased to 1500 and 3000 ppm. This study thus demonstrates the potential for surfactant-induced wettability alteration and spreading coefficient reduction in resolving condensate blockage problems.