An overview of hydrogen in the subsurface

Hydrogen is the most abundant element in the Universe. As a fuel and energy carrier it has had several false starts. Today it is thought to be on track to become a part of the future energy mix, with a multi-fold increase in usage estimated over the next 25 years. As this future develops earth science will play a role in both storage and production/manufacturing. Large-scale utilization of hydrogen will require subsurface storage. Currently, subsurface storage has largely focused on massive salt or salt diapirs. This is geographically limiting. To broaden storage opportunities bedded evaporites and porous media will need to play a role. Each subsurface storage type has multiple issues to be examined including the effects of the frequency and magnitude of drawdown, impact of microbial processes, reservoir and seal (caprock) diagenesis, and potential hydrogen losses. Storage space for hydrogen in porous media could potentially compete with CO 2 storage. On the production side there is growing interest in natural (white) hydrogen, the availability of water, especially freshwater, for electrolysis (green hydrogen), and the potential for anthropogenic (orange and gold) hydrogen in the subsurface. With respect to natural hydrogen, mechanisms and rates of generation are being investigated as is the common association with helium. Understanding the natural hydrogen system, including the trap, overlaps with issues of storage that focus on the reservoir and seal. The commercial subsurface stimulation of hydrogen generation is also being examined with respect to mechanisms and rates, with an aim of making it competitive with surface manufacturing. Large-scale production of natural hydrogen is yet to be established.One may ultimately view the current state of the subsurface hydrogen story being comparable to that of the initial stages of unconventional gas production more than two decades ago, with much still to be learned. • Hydrogen’s usage will increase over the next few decades increasing the need for underground storage in salt diapirs, bedded evaporites, annd porous media. • Natural hydrogen may play role in the hydrogen budget, it appears broadly distributed, but its commerciality has yet to be firmly established. • The use of the hydrogen system model for hydrogen exploration is complicated by the multiple modes of formation and their different sources. • Opportunities may exist for anthropogenically induced hydrogen generation in the subsurface. • The availability of water is site specific for green hydrogen and should be considered earlier in project assessment.