Pore-Scale Analysis of Interfacial Instabilities and Impact of Heterogeneity on Relative Permeability by Lattice Boltzmann Method

Interfacial instabilities occur often during immiscible fluid flow through porous media and their understanding is essential for waterflooding operations or other oil recovery processes. Although many studies including experimental and numerical have been done to reproduce and analyze the interfacial instabilities in porous median, there is still significant knowledge gap in fundamental understanding of these flow instabilities at the pore-scale. In order to better understand the interfacial instabilities phenomenon, the pore-scale simulations are performed. In this study, Lattice Boltzmann Method is used to simulate two different types of interfacial instabilities: viscous fingering and capillary fingering in irregular sphere packs by changing the viscosity ratio of the displacing and displaced fluid to achieve different force balances. A distinct feature of viscous fingering at the pore scale is that the wetting phase mostly flows through the pore space such that a sharp interface between immiscible fluids in pore space is observed while it sporadically moves along the grain surface. In contrast during the capillary fingering instabilities, the wetting phase moves mainly along the grain surface. Further, the fluid flow paths during different instabilities can be significantly different even in the same porous medium. Also, the effective relative permeability is calculated while accounting for heterogeneity in the porous media. Based on the simulation results it was concluded that heterogeneity in porous media will in general lower relative permeability of wetting phase during the imbibition process but may not significantly influence the non-wetting phase relative permeability