Hydrogen storage in depleted oil reservoirs: Insight into bibliometric analysis, influencing factors, selection of cushion gas and potential sites

The utilization of subsurface structures for hydrogen storage offers viable options to maintain a balance between energy generation and consumption. These geological formations can provide a giga-scale storage capability and are capable of accommodating fluctuations in both hydrogen demand and supply. Among different subsurface storage options, depleted reservoirs emerge as one of the most economically viable and reliable options, owing to their extensive geographical presence, well-identified geological data and established surface infrastructure, which reduces the need for vast investments in new storage facilities. Nonetheless, our knowledge of depleted oil reservoirs as a storage formation is limited, and a thorough understanding of the mechanisms and parameters affecting storage integrity is essential. Herein, this review article discusses the key elements affecting storage efficiency including hydrodynamics, geochemical interactions, geomechanical and microbial activity. It also offers a brief summary of trapping mechanisms and discusses the role and behavior of cushion gas during subsurface storage. Additionally, it outlines selection criteria for cushion gas based on interfacial and wetting properties. Furthermore, it presents an overview of worldwide potential sites and provides an insight into bibliometric analysis highlighting the progress, research directions and gaps in the field of subsurface hydrogen storage. Based on the review, the technology of hydrogen storage in depleted oil reservoirs is still in its early stages and further research is essential particularly estimation of H₂ losses due to fluid-rock interactions and microbial factors.