Study on microscopic flow mechanism of polymer flooding

Abstract

Polymer flooding plays an important role in chemical enhanced oil recovery (EOR) methods, and has been widely used in oilfields, particularly Daqing, the largest oilfield in China. However, our understanding of the mechanism of polymer flooding is not very clear. The mechanism of a two-phase micro-flow remains a challenge to researchers, because the structural complexity of a porous medium and the rheological property of a non-Newtonian fluid can increase the difficulty in such research. Computational fluid dynamics provides a numerical simulation method for further investigating the mechanism of polymer flooding at the micro-scale. In this study, OpenFOAM was used to study the two-phase micro-flow of both water and polymer flooding. Based on a micro-physical model of a complex pore structure, the continuity equation, momentum equation, and non-Newtonian fluid constitutive equations of a two-phase flow are established, and the phase equation of the two-phase interface is then developed using the volume of fluid methodology. These equations are solved using the InterFoam solver in OpenFOAM. The saturation, pressure, and velocity distribution characteristics of water and polymer flooding were obtained. The results show that the high viscosity of a polymer solution improves the mobility ratio, inhibits the fingering phenomena, increases the displacement area, and improves the displacement efficiency. The breakthrough time of polymer flooding under a Newtonian rheological property occurs 0.3 s later than that of water flooding, and the displacement pressure drop is higher. When the flow reaches a steady state, the displacement pressure drop of polymer flooding under a Newtonian rheological property is five times that of water flooding, and the displacement efficiency increases by 8–20%. In non-Newtonian fluids with a shear thinning characteristic, where the viscosity of the polymer solution is reduced as compared with polymer flooding under a Newtonian rheological property, polymer flooding under a non-Newtonian rheological property occurs 0.1 s earlier, the displacement pressure drop is reduced by 300 Pa, and the displacement efficiency decreases 4%. These research results will provide a theoretical foundation for a micro-flow mechanism of a two-phase flow in a complex pore structure.