ABSTRACT
Abstract-The use of surfactants to enhance recovery of oil from petroleum reservoirs has been well documented in the literature. The two main mechanisms for oil recovery enhancement by surfactants are modifications in interfacial forces (interfacial tension) and surface forces (rock wettability). However, the ability of these surfactants to alter wettability, as well as the relative contributions from the two mechanisms on multiphase flow characteristics in porous media and enhanced oil recovery remain largely unexplored. Hence, flow experiments through porous media were carried out in two different rock-fluids systems using a nonionic ethoxy alcohol surfactant. The first system consisted of Berea rock, Yates synthetic brine and n-decane, in which wettability effects were assumed to be negligible; and the second system consisted of Berea rock, Yates synthetic brine and crude oil from the Yates reservoir in West Texas, with its accompanying wettability effects. The multiphase flow characteristics are represented by oil-water relative permeabilities. A coreflood simulator has been used to calculate oil-water relative permeabilities by matching the recovery and the pressure drop data obtained during these flow tests. The relative permeability variations have then been interpreted to characterize the wettability alterations induced by the surfactant. The significantly higher incremental oil recoveries, observed due to surfactant in the rock-fluids system containing Yates crude oil when compared to that consisting of n-decane, clearly demonstrated the wettability-altering capability of the surfactant in addition to confirming the hypothesis that the wettability alteration was the principal mechanism for enhancing oil recovery by the surfactants. In addition, this study has provided evidence that the surfactant was able to render a special kind of heterogeneous wettability, known as mixed wettability, that enables preferential draining of oil phase through the formation of continuous wetting films of oil on the rock surface. This study has also demonstrated the possibility of making erroneous wettability interpretations from relative permeability characteristics due to the strong impact of oil-water emulsions on flow dynamics.
