Investigating the dynamical stability of heavy crude oil-water systems using stirred tank

Abstract

In petroleum industry, the stability of oil-water emulsions has a significant influence on multiphase flow and oil-water separation; however, there is a lack of quantitative research on the stability of heavy oil emulsions under flowing conditions. Here, emulsion stability was characterized by the free water fraction, and experiments using a stirred tank were carried out to investigate the stability of heavy crude oil emulsions. Sensitivity analysis of different variables such as temperature, shear rate, emulsifier dosage, salinity, and initial water fraction of oil-water mixture were conducted by measuring the free water after stirring. Free water fractions under flowing conditions were determined by extrapolation of the separated water fraction to the precise moment when stirring was stopped. Additionally, the viscosity of emulsions under corresponding experimental conditions was measured by the method of stirring. It was found that for partially emulsified heavy oil emulsion systems, the stability of the system increased with the initial water fraction, salinity, shear strength and emulsifier dosage, and decreased with the settling temperature. Based on the experimental results, a preliminary water separating fraction model (to evaluate the stability of the heavy crude oil-water system) and a viscosity model were proposed. The power law equation might well fit the data with relative deviation below 13.75% and 7.28%, respectively. The stability evaluation model and viscosity calculation model may prove beneficial in estimating pipeline flow conditions, and helping to design transportation arrangements in industrial applications.