Abstract

Underground hydrogen (H2) storage is a prominent technique for enabling H2-based economy via offering a large-scale storage medium. Recently, volcanic basaltic formations have been investigated as a potential medium for gas storage due to their thickness, vast extension, and potential volumetric capacity. Wettability is one of the essential parameters studied to understand the capillary-entrapment of the stored gas in porous media. Therefore, in this study, we evaluate the wettability of rock/H2/brine system of two different saudi basaltic rock samples by measuring the contact angles using relevant reservoir brine (10% NaCl) under storage conditions at temperature of 323K and varying pressures (3 to 28 MPa). The measurements were conducted using the modified sessile drop method and surface roughness was determined to ensure accurate results. The results showed relatively low variation with pressure. Saud basalt-1 with higher Si-O-Si and hydroxyl group bondings from FTIR demonstrated better sealing conditions for H2 storage than Saudi basalt-2. Additionally, the pore throat radius has a proportional relationship with 𝑝𝑐𝑒 and ℎ𝑔𝑚𝑎𝑥. Smaller pore-size basaltic rocks are better for safe and secure storage, and a potential effective capillary entrapment of H2.

Introduction

Governments and countries worldwide are adapting strict environmental regulations to reduce harmful anthropogenic emissions of greenhouse gases such as carbon dioxide (CO2), attributed mainly to the burning of fossil fuels (Hashemi et al., 2021; IEA, 2018). Alternatively, hydrogen (H2) emerges as a promising clean fuel to support decarbonization by converting energy production from fossil fuels into a more environmental-friendly form and supporting clean energy from renewable resources such as wind turbines and solar power (Pan et al., 2021). However, wide-scale implementation of an H2-based economy requires a medium of Giga to Tera scale storage capacity, which can be theoretically offered by geological formations such as saline aquifers, depleted oil and gas reservoirs, and salt caverns (Heinemann et al., 2021).

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