Mechanism exploration of the hydrodynamic trapping of hydrogen in geological formations via the pore-scale numerical studies

Abstract

Storage of Hydrogen (H₂) in subsurface formations is essential for sustainable developments. To unveil the mechanisms behind the H₂ trapping potentials in underground reservoirs, pore-scale numerical studies are carried out with help of the digital rock technique and Computational Fluid Dynamics (CFD) approach. The H₂ displacing brine as well as the subsequent H₂ extraction behaviors are scrutinized in the complex pore geometries of the homogeneous and the fractured porous media. Numerical results show that, only after reaching a certain pressure drop, the injected H₂ could break through the brine saturated porous media. The fracture structure could help fulfill the gas flooding brine process at lower pressure drop of 1500 Pa against 2250 Pa in homogeneous porous media. With the similar displacement efficiency of 78.6 % in the fractured media against 79.1 % in the homogeneous core under the elevated pressure drop of 3000 Pa, the limited role of fracture presence on sweep efficiency improvement is observed. Due to the water wet of the fluid-rock system, the subsequent H₂ extraction process could be fulfilled at much lower pressure drop levels of 1–50 Pa with the gas trapping ratios below 10 %. Parameter investigation results show the reduction of the IFT and/or altering the H₂/brine/rock system from water-wet to intermediate-wet could help substantially the H₂ geological storage performances. It is expected the study findings could help understand in mechanism the complicated multiphase displacement characteristics in the complex pore geometries thus offer valuable insights on the H₂ geological storage practices.