A Novel Process for Demulsification of Water-in-Crude Oil Emulsions by Dense Carbon Dioxide

Abstract

CO2 was used to break several water-in-crude oil and water-in-model oil emulsions stabilized by asphaltenic films. The stability of asphaltenic films in model oils having varying H/C ratios (aromaticities) was also studied upon contact with liquid or supercritical CO2. The efficacy and kinetics of demulsification appeared to be enhanced with increased CO2 density and mole fraction. The proposed mechanism by which CO2 destabilizes water-in-crude oil emulsions involves asphaltene flocculation and precipitation. The emulsions break by flocculating the adsorbed asphaltenes, leading to film defects, film thinning, film rupture, and water coalescence. The various factors influencing asphaltene precipitation and emulsion destabilization were studied in model solvent systems containing asphaltenes and resins. Increasing CO2 pressure, residence time, temperature, and degree of mixing were found to increase the rate of asphaltene precipitation. Asphaltene precipitation by CO2 was found to increase in the presence of water as compared to precipitation from water-free systems. It is apparent that CO2 preferentially precipitates the most surface-active portion of asphaltenes, leading to a substantial weakening of the viscoelastic asphaltenic film built around the dispersed water droplets in the emulsion. The rate of the demulsification process was greatly enhanced when the emulsion was injected under pressure into compressed CO2 as a result of the enhanced CO2/emulsion volume ratio and mass transfer rates.