Emulsification Characteristics and Electrolyte-Optimized Demulsification of Produced Liquid from Polymer Flooding on Alaska North Slope

Abstract

The first-ever polymer flooding pilot test is currently implemented in heavy oil reservoirs on Alaska North Slope (ANS). One of the major concerns of field engineers is the impact of polymer on oil/water separation after polymer breakthrough. This paper aims to predict the influence of polymer on emulsification characteristics of produced liquid and seek a cost-effective method to treat the produced liquid from polymer flooding. In this study, emulsions, at moderate and vigorous shearing conditions, were prepared by mechanically mixing 25 vol% of the ANS heavy oil with 75 vol% of the polymer solution. Bottle test method, microscope, and pendant drop technique were utilized to investigate the effect of polymer on emulsification characteristics in terms of separation behavior, drop size distribution (DSD), and interfacial properties [i.e., interfacial tension (IFT) and interfacial dilational rheology], respectively. As for chemical demulsification, the performance and interfacial behavior of four commercial demulsifiers and an inorganic salt, that is, potassium chloride (KCl), was measured using simulated produced liquid. The bottle test results demonstrated that polymer could enhance the emulsion stability, resulting in a slower separation rate, poorer water quality, and greater thickness of the intermediate layer. The pendant drop measurements showed that the IFT and interfacial dilational rheology were independent of polymer concentration. Thus, the stabilization effect of the polymer was mainly attributed to the increased viscosity of the continuous phase and the decreased drop size of the dispersed oil phase. As for the chemical demulsification tests, compound demulsifier E12 + E18 exhibited the best demulsification performance as well as the lowest IFT and interfacial elastic modulus. Nevertheless, a multifold dosage of E12 + E18 was required to demulsify the emulsion under vigorous mixing, leading to a potential increase in the chemical cost. A less expensive electrolyte, KCl, was able to work synergistically with demulsifier E12 + E18 to promote oil/water separation and reduce the demulsifier usage. In this proposed demulsifier formula, the mechanism for the effectiveness of the commercial demulsifier was its destructive effect on the interfacial film, while the effectiveness of KCl was mainly dependent on its viscosity reduction effect on the continuous phase. This study illustrates the intermediate layer elimination, and the water quality is the major challenge for produced liquid from polymer flooding and provides both practical and theoretical guidance in advance for the corresponding demulsification strategy of the produced liquid from the ongoing first-ever polymer flooding pilot on ANS.