Effect of shear-thinning of non-Newtonian fluid on the crossover from capillary fingering to viscous fingering in porous media

In this study, we constructed the pore network model for simulation of non-Newtonian two-phase flow. The pore network is initially saturated with the Ellis non-Newtonian fluid and water is then injected with various capillary numbers to simulate water flooding. We observed that there is also a crossover from the capillary fingering to the viscous fingering. In the crossover, the invading fluid tends to fill large-radius pipes, forming a small number of flow paths and low invading fluid saturation. The results show that the stronger the shear-thinning of the Ellis fluid, the easier it is for the injected fluid to invade the smaller-radius pipe, thereby suppressing viscous fingering and increasing the displacement efficiency, resulting in a smaller crossover zone. The findings of this study can help for a better understanding of the complex fluid-fluid displacement patterns in porous media for improving geological CO2 sequestration and enhanced oil recovery.