Pore-Scale Modeling of Low Salinity Water Flooding in Porous Media Using the Lattice Boltzmann Method

Abstract Low salinity water flooding (LSWF) is an emerging technique for enhancing oil recovery (EOR) by modifying the ion composition or concentration of injected water. A large number of indoor experiments and field applications have confirmed that LSWF can effectively alter the wettability of rocks, thereby enhancing oil recovery during secondary and tertiary oil recovery stages. LSWF presents notable advantages compared to alternative EOR techniques, including its straightforward implementation, low costs, and environmentally friendliness. However, due to the complex interface reactions involved in LSWF, which is a coupling of multiple physical and chemical fields, there is still no consensus on the mechanism of this technology. In addition, there have been numerous cases of ineffectiveness in field applications. To address the aforementioned concerns, this paper proposes a lattice Boltzmann model (LBM) to simulate LSWF. The model employs the Shan Chen multiphase flow LBM model to simulate oil-water flow, while employing the passive solute method to simulate the convective diffusion process of low salinity water. At each time step, the Shan Chen model is used to solve the two-phase flow equation and calculate the main macroscopic variables. Subsequently, the advection-diffusion equation is solved to calculate the concentration field. Finally, the host program is returned for the next time step calculation. In order to verify the accuracy of the model, the simulation data is compared and validated with publicly available LSWF experimental data. Based on the lattice Boltzmann numerical model for LSWF, the calculation of microscale oil-water distribution and relative permeability curves is conducted, allowing the analysis of the microscopic processes of fluid flow and wettability alteration in porous media. The results demonstrate that the lattice Boltzmann numerical model for LSWF can accurately describe the microscopic process of wettability alteration, which is in good agreement with experimental observations. The numerical value of relative permeability depends on the pore geometry and the interaction between the two-phase fluids. Low salinity water exerts a certain regulatory effect on wettability, mainly caused by local adsorption-desorption imbalance. It effectively strips off a portion of oil films adhering to the rock but does not alter the primary flow paths. The microscopic low salinity water flooding model established in this paper achieves coupling of multiple physical fields, effectively characterizes the physical and chemical processes of oil-water two-phase flow, wetting alteration and solute adsorption-desorption. This elucidates the microscale flow mechanisms and influencing patterns for enhancing oil recovery through LSWF.