Comparative investigation of water and gas flooding in tight oil reservoirs: a pore-scale perspective

Tight oil reservoirs present significant challenges for efficient hydrocarbon recovery due to their low permeability and strong capillary effects. This study investigates the pore-scale difference of gas and water flooding by employing both capillary bundle and Lattice Boltzmann modeling. The results reveal that the relative efficiency of gas and water flooding is strongly dependent on pore scale, heterogeneity, and injection pressure. In homogeneous porous media, gas flooding outperforms water flooding at low to moderate pressures due to higher mobility and lower capillary resistance. At moderate to high injection pressures, water flooding gradually improves as capillary barriers weaken, leading to a transition in the optimal displacement strategy. The threshold pressure for optimal flooding significantly decreases with increasing pore size. In heterogeneous porous media, preferential flow paths intensify gas channeling, which weakens performance of gas flooding by causing inefficient displacement and early breakthrough. This further lowers the threshold pressure for water flooding, reinforcing its superiority in highly heterogeneous systems. LBM simulations further demonstrate that pore connectivity plays a crucial role in determining recovery efficiency, a factor not captured by traditional capillary bundle models. These findings highlight the importance of considering pore-scale heterogeneity and injection pressure constraints in enhanced oil recovery (EOR) applications.