Effect of rock surface wettability on hydrogen-cushion gas adsorption with application to hydrogen storage in depleted oil and gas reservoirs

In this study, adsorption capacity of Berea sandstones varying wettability states with respect to hydrogen (H2) and hydrogen-methane (H2-CH4) mixture are examined to assess the viability of depleted oil and gas reservoirs for large scale hydrogen storage. We investigate pure hydrogen and hydrogen-methane mixture adsorptions as a function of pressure, temperature, and rock surface wettability. The obtained results indicate that as the CH4 fraction increases from 0 to 20 %, the gas uptake exhibits a more significant rise, going from 0.98 to 1.68 cm3/g for oil-wet sandstone and from 1.04 to 1.2 cm3/g for untreated samples, both at 25 degrees C. This suggests a pronounced affinity of CH4 for the aged rock. The adsorption capacity of the H2-CH4 mixture increases from 1.2 to 1.68 cm3/g at 80 bar and 25 degrees C when rock samples are exposed to crude oil compared with the untreated rock samples. Investigating the impact of temperature on adsorption capacity reveals a decrease in gas uptake as the measurement temperature rises from 25 to 60 degrees C across all pressure levels. All rock samples exhibit a positive hysteresis in adsorption and desorption isotherms at various temperatures. The Freundlich, Redlich-Peterson, and Sips models are found to be more representative in describing the adsorption characteristics, suggesting multilayer adsorption on the rock surface. Our findings provide insights into the impact of natural gas adsorption and desorption on overall hydrogen production. This study can improve the accuracy and efficacy of reservoir simulations and flow models that depict the movement of hydrogen and natural gas through porous media within sandstone reservoirs.