Effective viscosity prediction of crude oil-water mixtures with high water fraction

Abstract

In the petroleum industry, a flowing crude oil-water system with high water fraction usually does not exist as a stable and homogeneous emulsion, but in the form of a mixture of oil and free water with some water being emulsified into the oil and thus, hydrodynamically, acting as part of the oil. Therefore, the existing viscosity models developed for stable and homogeneous emulsions cannot accurately predict viscosity of this kind of liquid-liquid mixtures. In the present work, the effective viscosity of crude oil-water mixtures with high water fraction was measured by using a stirring method. It was found that the effective viscosity of the mixtures decreased with increasing shear rate, water fraction and temperature. Based on the Taylor viscosity model and combined with our previous study on the emulsification behaviors of crude oil-water systems, a viscosity model was developed for crude oil-water mixtures with high water fraction, which is characterized in covering the effects of shear rate, emulsified water fraction and crude oil compositions. Validation was done by using 40 data points which were obtained from mixtures of two crude oils and not used for model development, and the results showed that the proposed model gave accurate predictions of the mixture viscosity, with an average relative deviation of 7.4%. Approach is proposed to application of this model in the prediction of the frictional loss of oil and water two phase flow in pipes.