Pore-scale simulation of multi-fluid flow transport dynamics for hydrogen geological storage in depleted gas reservoirs

Depleted gas reservoirs have the advantages of large reserves, good economic efficiency and well-established existing infrastructure, making them ideal scenarios for hydrogen geological storage. However, the flow and diffusion mechanism of hydrogen in the microscopic pores of the reservoir is still unclear, which restricts the optimization of storage efficiency and reservoir safety assessment. Therefore, this paper constructs a pore-scale fully coupled model considering the flow and diffusion of hydrogen, methane and brine, constructs digital rock samples with real cores, and systematically studies the migration and storage mechanism of hydrogen under different reservoir pressures, injection rates and wettability conditions. The study found that the flow of hydrogen and methane at the pore scale is significantly different, and hydrogen is prone to fingering and produces obvious gas mixing zones; although lower reservoir pressure is conducive to hydrogen diffusion, it may cause local non-uniform migration and affect storage safety; moderate injection rate can effectively reduce flow resistance and improve hydrogen storage efficiency; weak water-wet reservoirs are conducive to reducing flow resistance and viscosity loss, and improving hydrogen storage and recovery performance. The research results deeply reveal the correlation mechanism between the flow and diffusion laws of hydrogen and storage and transportation efficiency at the microscopic scale, which can provide theoretical support for safety assessment, reservoir selection and optimization of injection and production parameters in hydrogen geological storage projects.