Does Interfacial Viscoelasticity Increase Oil Recovery at High Temperature and Salinity in Carbonates?

Summary Low salinity water (LSW) injection may increase oil recovery in some crude oils. Despite the general belief that the mechanism of LSW is governed by wettability alteration, crude oil-water interfacial viscoelasticity appears to have a more dominant effect on oil recovery. The elasticity of the crude oil-water interface may be tuned by a very small amount of a polymeric surfactant (PS). In this work, we present a systematic investigation of viscoelastic interfaces in different crude oil-brine systems using four different crude oils (A, B, C, and D). The interfacial elasticity is measured for crude oil-LSW, crude oil-high salinity water (HSW), and crude oil-HSW with 100 ppm PS (HSW-PS). The measurements are conducted by shear oscillations of the interface at 25°C and atmospheric pressure. The PS may increase the elasticity of the crude oil-water interface significantly. Three of the crude oils (A, C, and D) show an increase in interface elasticity with 100 ppm PS in HSW. In one crude oil (B), there is no appreciable change in interface elasticity for HSW, LSW, and HSW-PS. We have conducted 15 different coreflooding experiments in carbonate rocks. Six experiments are carried out at 50°C, two at 90°C, and another five at 100°C. Experiments are conducted using stock-tank crude oil and formation water of very high salinity. We conduct two additional experiments at 100°C using live crude oil. The overall observation is that there is extra recovery from the addition of 100 ppm of PS to HSW injection. The extra recovery is in the range of 8–20% for oil displacement by the aqueous phase with high interfacial elasticity promoted by the addition of 100 ppm PS in HSW. The oil recoveries are found to be greater at high temperatures during the displacements of both stock oil and live oil with the use of 100 ppm of PS. Interface elasticity measured at 25°C may provide an indication of extra recovery at high temperatures.