Greenhouse gas intensity of natural hydrogen produced from subsurface geologic accumulations

Natural geologic hydrogen (H2) could supply climate-friendly energy. We perform a prospective life cycle assessment (LCA) of a generic natural H2 production and processing system, using engineering physics and chemistry to estimate greenhouse gas (GHG) intensity. Our baseline case gas contains 85 mol % H2, 12% N2, and 1.5% CH4. Well productivity, depth, and other parameters use data from US natural gas wells. We use an open-source LCA tool to model energy use and emissions. Site-boundary baseline GHG intensity is ∼0.4 kg CO2 equiv/kg H2 or ∼3 g CO2 equiv/MJ lower heating value (LHV) H2. The largest sources of GHGs are fugitive emissions and embodied emissions. Sensitivity analysis is performed by examining varying gas compositions, reservoir parameters, and production methods. Results are sensitive to CH4 content: a case with 75% H2 and 22.5% CH4 emits 1.5 kg CO2 equiv/kg H2. Other key drivers include sources of process energy and the handling and disposing of waste (non-H2) species. Natural geologic hydrogen (H2) could supply climate-friendly energy. We perform a prospective life cycle assessment (LCA) of a generic natural H2 production and processing system, using engineering physics and chemistry to estimate greenhouse gas (GHG) intensity. Our baseline case gas contains 85 mol % H2, 12% N2, and 1.5% CH4. Well productivity, depth, and other parameters use data from US natural gas wells. We use an open-source LCA tool to model energy use and emissions. Site-boundary baseline GHG intensity is ∼0.4 kg CO2 equiv/kg H2 or ∼3 g CO2 equiv/MJ lower heating value (LHV) H2. The largest sources of GHGs are fugitive emissions and embodied emissions. Sensitivity analysis is performed by examining varying gas compositions, reservoir parameters, and production methods. Results are sensitive to CH4 content: a case with 75% H2 and 22.5% CH4 emits 1.5 kg CO2 equiv/kg H2. Other key drivers include sources of process energy and the handling and disposing of waste (non-H2) species.