Review of reservoir challenges associated with subsurface hydrogen storage and recovery in depleted oil and gas reservoirs

Concerns regarding the anthropogenic levels of greenhouse gas emissions and their climate change consequences have forced the energy community to look for clean fuels and net-zero emission technologies. Hydrogen-based technologies are evolving and offer many benefits for addressing such issues. However, to do so, hydrogen supply is required in large quantities. Supply also comes with the challenge of where to store substantial quantities of hydrogen safely and securely. The large-scale storage issue can be addressed using subsurface hydrogen storage reservoirs which are ubiquitous. This paper holistically delves into the current state of research into such reservoirs and identifies the key approaches that are providing impetus to the maturity of the relevant applied technologies. Additionally, this review provides insight into the production of hydrogen at the subsurface level, which remains poorly investigated and understood.The status of underground hydrogen storage research is considered in terms of geochemical, microbiological, hydrodynamical, geomechanical, and reservoir scale simulation and experimental studies. The geochemical investigations suggest that available underground hydrogen storage technologies have not fully addressed the implications of changes in reservoir characteristics potentially occurring during storage. Microbial investigations establish how much hydrogen is consumed within realistic storage timeframes, how much reservoir clogging is likely to occur, and potential corrosion effects. Reservoir studies are typically simulation-based and mainly focus on operability and efficiency criteria. Simulation results are often supported by experimental studies performed to determine the reservoir formation contact angle, wettability dissolution, and diffusion effects. The review incorporates a bibliometric study to assess the status of research in subsurface hydrogen storage that reveals that most of the research themes addressed are either emerging rather than mature topics.