Effects of pore characteristics on water-oil two-phase displacement in non-homogeneous pore structures: A pore-scale lattice Boltzmann model considering various fluid density ratios

Abstract

Understanding immiscible-phase fluid displacement in non-homogeneous pore structures is crucial to enhance resource recovery in the secondary development of old petroleum reservoirs. Reducing residual oil resources requires quantifying the effects of pore characteristics on the development of preferential displacement paths in porous reservoirs, which can be used to predict the preferential path of water displacement during secondary oil recovery, and therefore, to design an effective plugging strategy. The non-homogeneity of pore structures of rocks makes it extremely difficult to directly observe the water-oil displacement in subsurface rock reservoirs and quantify the sensitivity of preferential paths to pore characteristics. As an effective alternative, numerical methods have been applied to explore the fluid displacement process in old petroleum reservoirs. In this study, a two-dimensional (2D) pore-scale multicomponent lattice Boltzmann model (LBM) was developed and used to study water-oil displacement in non-homogeneous pore structures that shared identical topological skeletons and porosities but had different pore size distributions and pore geometries. The effects of pore characteristics on the preferential displacement path of the water-oil imbibition were analyzed. The influence of the density ratios of incompressible fluids on the two-phase displacement was also compared. The comparison between the numerical results of different pore-scale models indicated that the variation of pore size distribution and pore geometry affects the development of water fingering and promotes different local displacement paths. The primary preferential displacement path remains unchanged in different pore structures, which can possibly be attributed to the invariant topological skeleton of the pore structures. The results demonstrate that the fluid density ratio dramatically influences the water-oil displacement behaviors and suggests coupling the real density ratio in an LBM simulation. This study provides a method to quantitatively evaluate the effects of pore characteristics on the water-oil two phase displacement in porous oil reservoirs and to help draft a strategy to enhance the resource recovery of old petroleum reservoirs.