Solvent Induced Oil Viscosity Reduction and Its Effect on Waterflood Recovery Efficiency

Abstract

WAG process is one of the techniques used for reducing gas consumption, enhancing recovery factor and achieving better profile control of displacing fluids. Recovery efficiency due to reduction of oil viscosity, simulating a WAG process, in a wide range of reservoir permeability and water injection rate was investigated. Gas viscosity reduction by miscible gas or solvent injection is mimicked by progressive dilution of a medium density crude oil with a mixture of hydrocarbon solvent. The porous media used in this study consists of a set of water wet sandstone core plugs of low to medium permeability. The experimental findings show that reduced oil viscosity has no correlation with recovery efficiency, in the normal flood velocity regime. However, in the higher flood velocity regime, recovery efficiency reduces with increasing oil viscosity, only for higher permeability cores, which is attributed to micro-heterogeneity within pore geometry. The study suggests that the additional oil recovery during miscible gas injection, is mainly contributed by the swelling factor of oil which results in increased oil saturation, higher reservoir pressure and increased relative permeability of oil in addition to the contribution from lower interfacial tension and very little, if any due to oil viscosity reduction. Key words: WAG process; Recovery efficiency; Oil viscosity