Effect of Cushion Gas on Hydrogen/Brine Flow Behavior in Oil-Wet Rocks with Application to Hydrogen Storage in Depleted Oil and Gas Reservoirs

Depleted oil and gas reservoirs have been recognized as prevailing alternatives to store hydrogen (H-2). However, only a few attempts have been perused to evaluate hydrogen storage in these formations. Our study is among the first to experimentally investigate hydrogen storage in oil-wet Berea sandstones under elevated temperature and pressure conditions. This study involves experimental investigations of hydrogen-brine steady-state drainage and imbibition relative permeability in the presence and absence of methane (CH4) as a cushion gas. Core flood experiments are also conducted to assess the effect of CH4 addition to H-2 on the formation pressurization effectiveness and the displacement of original fluids. Furthermore, we analyze the influence of hydrogen exposure on rock petrophysical properties such as porosity and permeability under subsurface conditions. Our findings show that adding 50% CH4 to H-2 improves gas relative permeability by 70.5%. The results also indicate that hydrogen storage and recovery are significantly enhanced with CH4. The gas saturation increases from 0.277 to 0.611 at the end of gas flooding with a 50%-50% H2-CH4 gas mixture. The addition of CH4 as a cushion gas considerably accelerates core pressurization during hydrogen injection, resulting in a reduction of 30.3% in the gas volume required to achieve 1000 psi pressurization. This study demonstrates minor alterations in the porosity and permeability of rock samples as a result of pure H-2 and 50%-50% H-2-CH4 exposure. The generated experimental data are crucial for predicting flow, optimizing storage and recovery, ensuring safety, supporting modeling, designing injection/extraction strategies, and understanding recovery techniques.