AA Mathematical Model for Emulsion Mobilization and Its Effect on EOR during ASP Flooding

Large-scale pilot tests of alkali-surfactant-polymer (ASP) flooding in the China’s Daqing Oilfield reveal that emulsification occurs during ASP flooding and displacement. The flow of emulsions in porous media exhibits high viscosity, well-behaved chemical stability, and apparent non-Newtonian flow features. The genesis and mobilization of emulsions in reservoirs are an important part of ASP flooding processes, and entrainment and capture of such emulsions in porous media are considered to be important for improving oil recovery by ASP flooding. However, there are few studies that attempt a quantitative description of emulsion mobilization in porous media. As a result, the physicochemical phenomena of emulsions are not included in the current numerical simulation of ASP flooding processes. Based on our experimental studies and field tests, we conducted an in-depth analysis of displacement mechanisms, emulsification, and flow behavior of emulsions in porous media during ASP flooding processes. In this paper, we describe the development of a mathematical model to describe such physicochemical emulsion phenomena. This mathematical model incorporates the mechanisms governing the interaction between emulsion droplets and pore structures, including emulsion genesis criteria, correlation of emulsion viscosity and water content, and permeability reduction caused by droplet capture. The model is implemented into an existing chemical reservoir simulator for numerical modeling studies of ASP flooding that considers emulsification mechanisms. Simulation results show that oil emulsification during ASP flooding has a significant impact on, and could improve, in situ oil displacement efficiency. The proposed model can be used for understanding the effects of emulsions in ASP flooding, within both laboratory studies and field applications. Introduction The result of laboratory testing and large-scale pilot testing of alkali-surfactant-polymer flooding shows that emulsification occurs with different intensities and characteristics. The flow of emulsions during ASP flooding processes exhibits high viscosity, high density and apparent non-Newtonian flow behavior. Laboratory tests show that oil emulsification of ASP flooding can improve interlayer and in situ interference, as well as oil recovery efficiency. Since emulsions play an important role in ASP processes, attempts have been made to simulate the process with increasingly complex compositional models. These models require a detailed understanding of the main effects involved during the ASP flooding process, and underscore the need for a mathematical model to describe emulsion mobilization during ASP flooding. Significant research has been carried out on the formation, stability and de-emulsification of ASP crude oil emulsions. However, very little work has been reported on mathematical modeling of emulsion flow through porous media, especially during chemical flooding processes. Furthermore, most of those studies have only considered the case in which emulsion is diluted and the only phase present in the system. Alvarado and Marsden introduced their bulk viscosity model, dependent on shear-rate, in which emulsion was considered to be a continuous, single-phase fluid. The so-called droplet retardation model was introduced by McAuliffe and used by Devereux, who modified the Buckley-Leverett theory for two-phase flow by including a retardation factor in the pressure driving force of the dispersed oil phase. However, within this model, the permeability of the porous media returns to its initial value when emulsion is followed by waterflood. Soo and Radke presented a filtration model describing the flow of stable, dilute emulsions in porous media. The formulas underpinning this filtration model are suited for droplet flow in a 100% brine-saturated porous medium, but do not consider the possibility of droplet generation from a residual oil phase present in the porous medium. By contrast, Islam and Farouq presented a model in which they considered emulsion as an independent phase. They also introduced permeability reduction as a step function of emulsion throughput and incorporated permeability reduction as a function of initial permeability. Their model,