Microscopic scale interactions of water ions at crude oil/water interface and their impact on oil mobilization in advanced water flooding

Abstract

In this study, we performed interfacial shear rheology, surface potential and oil droplets coalescence time measurements to investigate microscopic scale interactions of various individual water ions at both air-water and crude oil-water interfaces. The measured interfacial rheology data indicated completely different interfacial behavior at crude oil-water interface when compared to air-water interface due to the presence of crude oil functional groups. Viscous dominated response was observed at crude oil-water interface for all brine compositions. Lower interfacial viscous modulus was observed for certain key ions such as calcium, and magnesium. The interfacial viscous modulus was found to be substantially much higher for sulfates, besides exhibiting some elasticity. The surface potential was gradually decreased by replacing seawater with calcium only brine. The better surface activity with seawater can be attributed to adsorption of more key water ions at the surface.These interesting results observed with calcium and magnesium ions at crude oil-water interface are expected to favorably impact oil mobilization in advanced water flooding processes. Such favorable interactions can quickly destabilize the interfacial film between oil and water (due to less viscous interfaces) to promote the coalescence between released oil droplets and enable faster oil mobilization. This coalescence process is also sequential and it would continue until the formation of small oil bank. The coalescence times measured between oil droplets confirmed the adverse impact of sulfate ions, to hinder the coalescence and delay oil mobilization, in consistent with interfacial shear rheology results. The new fundamental knowledge gained in this study would provide an important guidance on how to synergize water ion interactions at fluid-fluid interfaces with those at rock-fluids interfaces and optimize advanced water flooding processes in carbonate reservoirs.