An Application of Superhydrophilic Coating to Enhance the Water Film Retention for Core Annular Flow

Abstract

Abstract The tremendous viscosity of heavy oil presents significant challenges to the pipeline transportation and efficiency improvement of oil gathering systems, thus prompting the execution of numerous studies that aim to reduce drag. The core annular flow is regarded as one of the most efficient and eco-friendly methods for drag reduction, but its commercial application is limited by the inadequate stability of the water film. In this work, a concept of water film retention enhancement at the pipe wall through superhydrophilic coating is presented, to increase the stability of core annular flow in heavy oil flowlines. Furthermore, a novel measuring method that efficiently evaluates the water film retention enhancement performance of superhydrophilic coating using a rheometer is proposed. This method is more effective, oil-saving, and sensitive compared to conventional flow loop tests. The influence of temperature, shear rate, and water film thickness on water film retention are studied. It was found that the viscosities measured with superhydrophilic coating decreased by approximately 40% at 50 °C and showed a reduced temperature-dependence, compared to the inherent viscosities of heavy oil. This decrease in viscosity was attributed to the lubrication provided by the water film. The viscosities measured with coating were also found slightly decrease with increasing shear rates from 10 to 120 s−1, indicating that the water film retention is enhanced by coating and the emulsification of heavy oil and water film is prevented even under strong shear. Moreover, it was observed that the water film thickness had a negligible impact on the measured viscosities as long as the water was sufficient to fully wet the coating. These results verify the feasibility of using superhydrophilic coating to enhance water retention and show a promising possibility of practical application of superhydrophilic coating in core annular flow for transporting heavy oil.