Subsurface technologies for hydrogen production from fossil fuel resources: A review and techno-economic analysis

To achieve the goal of net-zero emissions by 2050, vast investments are required not only in new infrastructure for renewable and low-carbon energy supplies but also in the gradual repurposing of significant fossil fuel assets. Conversion of depleted hydrocarbon reservoirs into underground energy conversion systems that are accessible through available well infrastructure offers a promising pathway to leverage these existing fossil fuel assets for a low-carbon energy future. One such approach is the production of hydrogen via in-situ combustion of hydrocarbons in the reservoirs. The hydrogen can be extracted from the wellhead while other gaseous products such as CO2 are left in the reservoir. A hydrogen-selective membrane allows for down-hole separation so that only hydrogen rises to the surface. Here, we present a review of subsurface technologies that can be used to produce hydrogen. A preliminary techno-economic analysis (TEA) is presented for a case of underground combustion and gasification of hydrocarbons in fossil-fuel reservoirs. This review article highlights the opportunities and challenges of producing hydrogen from this pathway. The TEA identifies key parameters that can have an impact on the overall process economics. These technologies open an area of research to investigate the technical aspects of subsurface hydrogen generation and production and assess the economic competitiveness of this pathway to bring low-carbon hydrogen to the market. This review evaluates the integration of subsurface hydrogen production systems with existing hydrocarbon production infrastructure and explains its potential market and environmental impacts.