Subsurface combustion and gasification for hydrogen production: Reaction mechanism, techno-economic and lifecycle assessment

Subsurface technologies present an excellent opportunity to produce hydrogen from hydrocarbon resources. It refers to the production of hydrogen directly from underground resources, particularly hydrocarbon resources. This method often involves injecting steam or oxygen into the reservoirs to initiate reactions that produce hydrogen. In some cases, subsurface method can also involve the process of in-situ gasification (ISG), and in-situ combustion (ISC) (also known as subsurface combustion and gasification). The produced hydrogen is extracted from the reservoir, leaving the carbon dioxide and other byproducts underground. This approach could offer a sustainable and carbon-free pathway to produce hydrogen because of reduced CO2 emissions compared to conventional methods. A comprehensive review of the status and progress of ISC and ISG of hydrocarbon for hydrogen production is presented. The advantages and limitations of the technologies were discussed as well as the underlying reaction mechanism. Techno-economic and lifecycle assessment studies of ISG and ISC are presented. One of the main economic limitations of subsurface hydrogen production is the high cost of building and operating the required infrastructure. However, utilizing pre-existing horizontal wells for air or oxygen injection can significantly reduce the initial infrastructure investment costs. Moreover, the overall process cost of ISG can vary significantly due to various factors, including membrane costs, oxygen production costs and the cost of hydrocarbon. The findings from the environmental evaluation indicate that the primary contributors to greenhouse gas emissions in subsurface technologies are the CO2 emissions produced during gas combustion for heat generation and the electricity consumed during the gasifying agents' preparation stage. Subsurface methods for producing hydrogen encounter numerous challenges, including choosing the right locations and selecting costeffective drilling techniques.