InterPore2025

Hydrogen Adsorption in Nanoporous Geomaterials Using Low-Field NMR and GCMC Simulations – Implications for Storage

19 May 2025, 17:55

15m

Oral Presentation (MS23) Advances in Experimental, Computational, and Analytical Approaches for Underground Hydrogen Storage MS23

Speaker

Camilo Guerrero (Geosyntec Consultants)

Description

Abstract. The conventional gravimetric and volumetric methods used for gas adsorption analyses are unable to differentiate between adsorbed and free gas behaviors and often rely on estimated adsorbed gas densities from molecular simulations for high-pressure corrections. This study introduces a novel approach using low-field Nuclear Magnetic Resonance NMR to gain deeper insights into high-pressure hydrogen H2 gas adsorption in geomaterials. Our focus lies on gas pressures relevant to near-surface and geological storage applications, which typically range across several MPa. This study employs NMR measurements to investigate the H2 adsorption capacity and the average density of the adsorbed H2 monolayer in high-specific-surface-area shales. The analysis is extended to sodium bentonite, illite-smectite, kaolinite, and activated carbon to represent key shale components. Complementary adsorption simulations using Grand Canonical Monte Carlo GCMC on analogous mineral surfaces were employed. Unlike other 1H-containing gases, results reveal two distinct relaxation mechanisms of H2 gas in porous media: a time-invariable short relaxation indicative of H2 monolayer adsorption, and a pressure-dependent long relaxation attributed to free H2 gas in pores. The absolute H2 adsorption capacity increases progressively from reactive shales to high-specific-surface-area clays and activated carbon. Notably, H2 storability improves significantly in bentonite at high pressures and in activated carbon across all pressures. Moreover, NMR-derived densities of adsorbed H2 show values 2.5 to 4 times greater than those of bulk H2. In addition to the mineral specific surface area, this study highlights the influence of adsorbate molecular packings, molecular orientation distributions within the adsorbed layer, and mineral surface homogeneity on H2 gas adsorption. Our laboratory results have potential applications for interpreting downhole NMR characterization tools in field studies.