Pore‐Scale Investigation on Two‐Phase Flow Mechanism for Underground Hydrogen Storage in Depleted Gas Reservoirs: A Multiple Parameters Analysis via Phase‐Field Method

ABSTRACT Understanding the gas‐water two‐phase flow mechanism with multi‐cycle flooding scenario is crucial for enhancing hydrogen recovery and storage ability during underground hydrogen storage (UHS) in depleted gas reservoirs. In this study, a two‐dimensional (2D) porous medium with real shape pore structure was extracted from the computed tomography (CT) image of a sandstone and reconstructed for numerical simulation. The multi‐cycle gas‐water flooding process was simulated to study the hydrogen storage and withdrawal. During the hydrogen injection process, a multiple parameters analysis was performed to evaluate the effects of capillary number, wettability, viscosity ratio, and interface tension on the hydrogen‐water flow characteristics and hydrogen occurrence state. The micro‐dynamics evolution of fluids interface was quantitatively characterised and comprehensively analysed during hydrogen storage process. Inheriting the simulation results of hydrogen storage process, the hydrogen withdrawal process was simulated consequently. The hydrogen recovery performance was analysed and compared in an integrated way with different flooding phases (i.e., water and CO 2 ). In addition, the effects of wettability and flooding parameters (injection pressure and velocity) on hydrogen recovery were systematically evaluated respectively. These findings reported in this study can help to provide technical support for optimising the hydrogen injection and withdrawal strategies, which are of certain guiding significance for engineering practice of UHS.