PORE-SCALE MODELING OF NON-NEWTONIAN FLUID FLOW IN POROUS MEDIA

Abstract

Understanding the effects of various interfacial and rheological parameters on a fluid flow inside a porous system is critical for a variety of industrial applications, including petroleum engineering, soil remediation, or biomedical engineering. This study conducts a series of numerical simulations of immiscible two-phase flow in a porous medium to investigate the influences of these parameters on pressure gradient and oil recovery efficiency. The HBP model is used to define a non-Newtonian fluid with a shear-thinning behavior and initial yield stress. Coupled Navier-Stokes and Cahn-Hilliard equations were solved by FEM in COMSOL Multiphysics. This study considers four different geometries beginning with a simple model of a fluid flow in a regular tube and proceeding with more sophisticated geometries. Starting with simple models we noticed that system pressure increased from 1520 Pa for the “m=10” up to 14700 Pa and 147000 Pa for the cases of m=100 and m=1000, respectively. Afterwards, we observed the same trend for the higher yield stress fluids of 100 N/m and 1000 N/m. However, this trend was not consistent for the shear-thinning fluids with a yield stress less than 1 N/m. Furthermore, the numerical results showed that maximum pressure increases by a factor of three each time we increase n by 0.25. Later, more complicated models were introduced to analyze the effect of rheological parameters on the final oil recovery. Thus, we recorded total oil recovery of 62% and 68% for n equal to 0.25 and 0.75, respectively. Additionally, oil recovery was improved from 70% to 87% when m was increased from 0.001 Pa∙s to 0.1 Pa∙s. It was concluded that injection of higher viscosity fluids leads to better sweep efficiency, preventing an early breakthrough and resulting in higher oil recovery. In addition, better oil recovery was achieved from the homogeneous geometry (>70%) defined by circular grains compared to the heterogeneous geometry (<70%), which represents real reservoir structure. The research results showed that higher injection velocity (0.01 m/s) may lead to oil trapping, leaving many areas totally or partially unswept. Meanwhile, lower injection velocity (0.001 m/s) resulted in higher displacement efficiency, preventing oil trapping. The findings confirmed that oil recovery can be improved by setting a lower contact angle closer (pi/4 or pi/5), which represents a water-wet system where oil droplets are not strongly attached to the wetted wall. On the contrary, a higher contact angle (3*pi/4) represents an oil-wet system where oil is more prone to being trapped on the surface, leading to poor sweep efficiency. Displacing fluid had more resistance to flow under higher IFT conditions, resulting in the fingering phenomenon closer to model centerline. Oppositely, lower IFT (<0.01 N/m) improved sweep efficiency due to increased capillary number, which is defined as a ratio of viscous forces to capillary forces. The numerical models considered in this study are in a good alignment with each other. The results demonstrate that rheological and fluid interface parameters can significantly affect oil displacement efficiency in a porous medium, underlying the need for accurate solver configurations and geometry considerations.