Study on multi‐cycle gas‐water displacing mechanism in underground gas storage of low‐permeability reservoir based on PNM.

A deep understanding of the pore‐scale multi‐cycle two‐phase seepage mechanism of gas‐water systems in low‐permeability reservoirs is crucial for enhancing oil and gas recovery and optimizing the operating conditions of underground gas storage. A pore network model was reconstructed using micro‐CT images of low‐permeability core samples from the Dagang Oilfield, China. The mathematical models of gas‐water flow in the pore‐scale models were established based on Poiseuille's law and the quasi‐static displacement theory, considering the gas compressibility and slip effects. The porosity, pore size, absolute permeability, and relative permeability (Kr) of oil‐water and gas‐water were calculated using pore network simulations and validated against experimental benchmark data of the same samples. The effects of multi‐cycle displacement, rock wettability, and average pore pressure on the gas‐water two‐phase flow were simulated and analyzed. The results showed that the relative permeability of gas (Krg) at the same water saturation level significantly increased when the gas compressibility and slip effects were considered. With an increase in the number of gas‐water displacement cycles, Krg at the same water saturation level showed a decreasing trend, indicating a reduction in the gas seepage capability. Krg decreased with increasing water contact angle. With an increase in the average pore pressure, Krg decreased and gradually increased when the average pressure exceeded 25 MPa. [ABSTRACT FROM AUTHOR]