Numerical modeling of viscous fingering during miscible displacement of oil by a paraffinic solvent in the presence of asphaltene precipitation and deposition

Abstract

We study the mixing dynamics of a paraffinic solvent with oil in the context of miscible displacement in porous media for enhanced oil recovery. Typically, injected solvents are less viscous compared to the resident oil, leading to the rise of interfacial instabilities known as viscous fingering. This, in turn, accelerates precipitation of initially dissolved asphaltene particles in the oil. The formed precipitates are carried with the flow and may deposit in the porous media, altering porosity and permeability fields. Although asphaltene precipitation and deposition are inevitable in most of the solvent-based recovery techniques, they have been neglected in the previous works of miscible displacement due to their added complexity. In this work, we present a rigorous formulation of the physics of the problem and conduct high-resolution nonlinear numerical simulations to investigate the effects of asphaltene precipitation and deposition and the resulting formation damage. For this purpose, the related governing equations are derived based on the velocity-vorticity formulation, and a high-order hybrid scheme is applied to solve them. This type of handling enables us to simulate viscous fingering at large viscosity ratios and Peclet numbers, beyond what has been previously reported in the literature. Furthermore, experimental measurements are conducted for viscosity and asphaltene content of the oil at various solvent concentrations and are used in the simulations. The results of our numerical simulations reveal that despite having a great impact on the permeability field, asphaltene precipitation and deposition do not influence the growth of viscous fingers, noticeably, which is due to the substantial viscosity ratio of the studied system. However, deposition of the formed precipitates leads to in-situ upgrading of the oil and thus enhances the quality of the produced liquid. Finally, regarding the effect of the choice of viscosity mixing rule, we compare two commonly used viscosity mixing rules in the previous works (exponential and quarter-power) and elaborate on their main differences in terms of the observed dynamics.