Low Carbon Intensity (LCI) Hydrogen (H2) offers the potential for a transportable, storable energy carrier and feedstock to help realize a low carbon economy. LCI hydrogen can be produced by electrolysis with electricity generated from solar, wind, hydro, or nuclear power plants, from steam methane reforming or from coal gasification technologies using fossil fuels (primarily natural gas), which when coupled with carbon capture and storage (CCS) systems reduces the carbon intensity. Approximately 95 % of the current US hydrogen production (almost all without CCS) is generated by steam methane reforming for industrial applications such as petrochemical refining and chemical manufacturing. Other LCI hydrogen production technologies such as pyrolysis of natural gas or biomass are emerging. In addition, subsurface-focused hydrogen technologies including exploration and production of geologic hydrogen, in situ hydrogen generation from hydrocarbons and coal coupled with CCS, and geo-stimulated in situ hydrogen production by serpentinization reactions are being actively investigated and pursued.
The subsurface already plays a significant role for hydrogen storage in the US with three underground hydrogen storage facilities in dedicated salt caverns in the Texas Gulf Coast region. These facilities are used to reliably supply hydrogen for refining and petrochemical manufacturing. With the goal of further reducing CO2 emissions, the development of LCI hydrogen value chain pathways for hard-to-abate industrial applications such as chemical manufacturing, for back-up and peak power generation, and for heavy-duty transportation will require significant expansion of hydrogen infrastructure including geological storage. Natural gas-based steam methane reformed LCI hydrogen will require CCS with large-scale CO2 (permanent) geological storage. Although salt cavern storage is proven and viable for hydrogen, it is limited to those regions with thick bedded or domal salt deposits where dissolution caverns can be developed or repurposed. Depleted gas/oil fields, and saline aquifer (porous media) reservoirs, which are used extensively for natural gas storage, provide an alternative for hydrogen storage offering broader geographic coverage. However, research is required to assess hydrogen’s physical and chemical behavior in these reservoirs, and also to understand the effectiveness of top and lateral seals for hydrogen. In addition, testing of advanced geophysical monitoring technologies for geologic hydrogen storage is needed.
Beyond hydrogen storage, emerging technologies and concepts including in situ generation of hydrogen from fossil fuels coupled with CCS, in situ generation of hydrogen from ultramafic igneous rocks, and exploration for and production of naturally occurring hydrogen provide opportunities to unlock the subsurface for LCI hydrogen in the future. High concentrations of hydrogen in syngas from underground coal gasification, and from in situ combustion in oil fields have demonstrated that hydrogen under the right conditions can be produced in situ. Natural serpentinization of ultramafics produce hydrogen, and the potential to geo-stimulate serpentinization in the subsurface to abiotically generate LCI hydrogen is a topic of active research. Finally, exploration for geologic hydrogen resources is underway around the globe. A high concentration hydrogen gas field has been drilled and developed in Mali, and recent exploration ventures have reported hydrogen occurrences in North America, South America, Eurasia, and Australia.
The expected need for large-scale hydrogen storage, and the emerging opportunities of geologic and geo-engineered LCI hydrogen affirm the importance of the subsurface and subsurface disciplines to unlocking the hydrogen value chain of the future.