ABSTRACT

In the global transition of energy sector, hydrogen is gaining attention as a promising and environmentally friendly fuel. It has also exhibited the potential for storing excess renewable energy for meeting the fluctuating demands. The growing need for hydrogen in the current era of decarbonization has necessitated the requirement for its large-scale storage. Due to its extremely low density and viscosity, hydrogen storage poses a significant challenge in the energy industry. Underground storage locations, such as salt caverns, saline aquifers, and depleted reservoirs, have the capacity to store hydrogen on a vast scale, and extensive research is being conducted in this area. The hydrogen storage capacity and containment security of underground sites are significantly influenced by the wettability of the rocks in the reservoir. Contact angle measurement is employed to quantify the hydrogen wettability in reservoir systems. Studies have been conducted to determine the wettability of H2/brine/rock system over a wide range of realistic conditions. It has been found that the ions present in the formation brine can alter the wettability of reservoir rock during storage of gases. Hence, during the storage of hydrogen in underground sites, sufficient knowledge is required on the interaction of formation brine and the ions present in it under reservoir conditions and the alteration in wettability it can bring into the system. Hence, this study investigates the effect of Na+ and Ca2+ ions on the change in wettability and storage capacity of hydrogen in underground sandstone reservoirs. The effect of varying salinity is also studied. The results demonstrate that the presence of these ions under varying salinity conditions leads to a noticeable alteration in the wettability of the H2/brine/rock system. The findings of this study, which is a component of the ongoing investigation on underground hydrogen storage in depleted reservoirs, will deliver new insights into the successful storage and optimal retrieval of hydrogen during geo-storage.

INTRODUCTION

The growing need and utilization of energy will eventually result in the depletion of fossil fuels, necessitating the exploration of alternate energy sources. Moreover, the rise of 1.5 degrees Celsius in the mean atmospheric temperature compared to pre-industrial levels has necessitated a transition from fossil fuels to low-carbon alternatives (Mouli-Castillo et al., 2021). In this context, hydrogen as a zero-carbon fuel is grabbing immense attention. It is also used as the storage option for excess of renewable energy. During the current phase of extended research into ways for producing green hydrogen on a large scale, there is also a notable focus on finding practical storage solutions for this type of hydrogen. Underground storage of hydrogen in salt caverns, depleted reservoirs and saline aquifers is considered as a suitable solution for this. Given the understanding of the current infrastructure for extracting hydrocarbons, depleted hydrocarbon reservoirs are the most suitable choice among all the existing geo-storage solutions for hydrogen. Based on the capital cost evaluation, it has been determined that depleted oil and gas reservoirs are the most economically efficient choice for storage. The anticipated cost for this storage is around $1.29 per kilogram of hydrogen (Epelle et al., 2022). The extensive size, significant porosity, impermeable caprock, and tightness of oil and gas reservoirs, which effectively traps the stored gas makes them potential candidates for subterranean hydrogen storage (Epelle et al., 2022; Navaid et al., 2023; Perera, 2023).

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