Study on the indigenous stabilization mechanism of light crude oil emulsions based on an in situ solvent-dissolution visualization method

Abstract

The produced fluid from reservoirs are generally in the form of emulsion with oil and water, in which indigenous components such as asphaltene, resin and wax can act as natural emulsifiers. In this study, water-in-oil emulsions were prepared with five light crude oils from CQ Oilfield respectively, and investigated to identify the indigenous stabilization mechanism based on a novel visualized method by in situ solvent-dissolution (ISV). The emulsion stability was studied by dehydration rate and droplet size via bottle test and microscope. Saturate-Aromatic-Resin-Asphaltene (SARA) separation, wax appearance temperature (WAT) measurement, and gas chromatography were applied to characterize the indigenous components in the crude oil. Colloid instability index was introduced to analyze the solubility of asphaltene. Furthermore, the stabilization mechanism of the oil emulsion was investigated by ISV method in both macroscopic and microscopic scales via dilution by n-heptane and toluene. The viscosity of oil, interfacial viscosity, interfacial storage and loss modulus were measured by rheometer to evaluate the contribution of the stabilizer quantitatively. The results showed that emulsion stability increased with the concentration of asphaltene, especially over a critical concentration. This ISV method provides a convincing approach to understand the indigenous stabilization mechanism of original crude emulsion vividly rather than that in the model emulsion. The interfacial viscosity, viscoelasticity or oil viscosity increased with asphaltene concentration in the crude oil. The strong elastic interface film formed with asphaltene restricted the droplet coalescence and controlled the stability of emulsions, which was found to be the crucial stabilization mechanism. Asphaltene and its concentration are the dominating factors of stability of these light crude oil emulsions. This work not only clearly clarifies the significant role of asphaltene in the stability of light crude oil emulsions, but also proposes a convenient in situ method to study the emulsion stabilization mechanism.