Effects of Ionic Interactions on the Stability and Destabilization of Water-In-Crude Oil Emulsions

Abstract

Abstract Water-in-crude oil emulsions are formed as a result of high shear stresses at the flow restrictions such as choke valves and the wellhead during crude oil transport with produced water. Consequently, the produced water disperses in the crude oil forming droplets that are stabilized by the natural surfactants/emulsifiers in the crude oil. Emulsion droplets undergo spherical to ellipsoidal shape deformation and subsequent break up to smaller drops during flow. Droplet deformation is often resisted by the interfacial tension as determined by the Laplace pressure. The droplets will coalesce if they are attracted and adhered together but will become stable if repulsion between them dominates. However, the application of droplet-droplet interactions has not been adequately exploited for formulation of environmentally friendly chemical demulsifiers. This work investigates the effects of ionic interactions of droplets on the stability and destabilization of water-in-crude oil emulsions. Properties of the crude oil used in this work were measured and correlated to the properties of the resulting emulsions at different water cuts and salinities. The stability of the emulsions was determined by examining the sedimentation and coalescence of emulsion droplets in bottle tests and backlight scattering methods. The breakage of the droplets was examined by conducting the rheology profiles of the emulsions. Subsequently, the emulsions were destabilized with sodium methyl ester sulfonate (SMES) at 70°C. SMES and is an anionic chemical material that is locally available, environmentally friendly and possess potential demulsifying properties. Results show that the emulsions were kinetically stable since the droplets remained highly dispersed and were characterized by diffusion–sedimentation subsequent equilibrium. Destabilization of water-in-crude oil emulsions is mostly a function of droplet momentum and the viscous force presented by the continuous phase. Thus, inducing ionic charges in emulsion systems can significantly enhance the force of attraction among emulsion droplets which leads to improved phase separation.