Numerical simulation of residual oil distribution and mobilization during pore-scale water flooding

Abstract

In order to reveal the characteristics of oil and water two-phase transport and the law of residual oil in the process of micro-water oil driving, this paper establishes a two-dimensional micropore scale numerical model, uses the Level Set method to track the oil-water interface, and sets four groups of 0.5, 1.0, 2.0 and 3.0 MPa injection pressure conditions, simulates the dynamic process of water phase driving oil phase, and analyses the oil-water distribution, residual oil endowment form and oil phase extraction degree changes under different injection pressures. The simulation results show that the water phase does not advance evenly after entering the pore space, but prioritizes to moving along the hole throat channel with good connection and small flow resistance. With the increase of the injection pressure, the range of water phase wave gradually expands, and the continuous oil phase is constantly squeezed, peeled and divided, and the residual oil gradually changes from a large-scale continuous sheet or lumpy distribution to a local lumpy and isolated distribution. The degree of oil phase extraction increases with the increase of the injection pressure, from 25.18% under 0.5 MPa to 45.66% under 3.0 MPa conditions, but the increase gradually decreases. Further analysis shows that increasing the injection pressure can enhance the spillover ability of the relatively small throat channel and lateral pores of the water; however, after the formation of the dominant channel, the subsequent injection water is more likely to flow along the low-resistance channel, and it is still difficult to fully use the residual oil in the blind end pores, the corner of the pores and the local low-speed area. The research results can provide a basis for the understanding of the mechanism of residual oil formation and the optimisation of water injection pressure on a microscale.