Enhanced oil recovery by emulsion injection in heterogeneous heavy oil reservoirs: Experiments, modeling and reservoir simulation

Abstract

Many of western Canada's heavy oil reservoirs are too thin to allow expensive thermal recovery techniques. Therefore, waterflooding is still often employed in heavy oil reservoirs due to its relatively inexpensive and easy manipulation. However, heterogeneity in permeability and/or in water saturation has been widely encountered in heavy oil reservoirs, resulting in very poor oil recovery with excessive water production. In this study, performances of enhanced oil recovery (EOR) by injection of oil-in-water (O/W) emulsions in heterogeneous heavy oil reservoirs were evaluated through experiments, modeling and reservoir simulation. For experiments, each O/W emulsion was firstly characterized via its stability behavior, emulsion quality, oil-water interfacial tension (IFT), oil viscosity, and droplet size distribution. Parallel-sandpack models with two different types of heterogeneities, either in oil saturation or absolute permeability, were applied to simulate the heterogeneity in heavy oil reservoirs. Experimental results show that injection of the emulsions is effective to recover the by-passed oil in the water-unswept sandpack and the EOR performance is strongly dependent on the emulsion characteristics. In order to achieve optimal oil recovery, a conformance in water mobility (outflow percentage ratio of 50%:50%) is found to be effecitve in the parallel-sandpack with heterogeneity in permeability. In parallel-sandpack with variations in water saturation, a strong blockage in high water saturation sandpack with a long penetration distance contributes an optimal oil recovery. An in-house simulator was developed based on an optimized emulsion flow model, for the first time, to be able to describe the physics of emulsion-assisted EOR in heterogeneous porous media. The simulation results show that emulsion injection in parallel-sandpack causes a greater average permeability reduction in the high water mobility sandpack resulted from longer emulsion slug penetration compared to that in the low water mobility sandpack. This leads to an increased water flood rate in the low water mobility sandpack, resulting in more oil production. A case study of emulsion flooding for EOR in a heterogeneous heavy oil reservoir was conducted. Strategies for optimal EOR in heterogeneous heavy oil reservoirs were discussed. Reservoir simulation results show that a greater ratio of emulsion slug in high water mobility zone to that in low water mobility zone is beneficial for EOR with a fixed emulsion plugging strength. For a given emulsion slug, there exists an optimal emulsion plugging strength for a prime EOR which can be designed through the optimized emulsion flow model.