Fluid retention on miscible viscous fingering of finite slices in porous media with dead-end pores

One of the key factors for low efficiency in miscible displacements is viscous fingering (VF), a hydrodynamic instability when a less-viscous fluid displaces a more-viscous one. While leading to large unswept areas by VF, it is widely believed that in swept areas the displaced fluid is 100% cleaned up. This is however not true considering the fluid retention caused by non-negligible dead-end pores in porous media. Here, we investigate by highly accurate numerical simulation the effects of fluid retention on VF of a finite slice. We employ a dead-end pore model that is different from the classical convection-diffusion equation. We find porous medium first acts as a sink and then a source of displaced fluids in newly swept areas, which substantially affects VF dynamics and leads to much more uncleaned displaced fluids in swept areas. Our research provides new insights into the roles of porous media in VF research community.