Other key drivers include how the process is powered and fueled, and the methods of handling and disposing of the separated non-H2 species. We find that results are most sensitive to the gas composition – mainly the amount of H2 and CH4 in the raw gas stream.

Sensitivity analysis is performed by examining varying gas compositions, as wells other resource parameters and production methods. The largest sources of GHG emissions are fugitive losses from the system and embodied emissions in constructed wellbores and equipment. GHG per kg of H2 produced for the baseline case, or ~3 gCO2eq./MJ LHV H2. Producing, dewatering, separating, and (if needed) compressing the gas results in a site-boundary GHG intensity of ~0.4 kg CO2eq. We use a modified version of the OPGEE open-source oil & gas life cycle assessment tool to model the energy use and emissions from geologic hydrogen systems. We set baseline productivity, depth, and other producing parameters using data from US natural gas wells drilled to date. Our baseline case includes gas with 85 mol% H2, and remainder N2 (12%) and CH4 (1.5%) and other inert gases (1.5%). While it is still too early in the development cycle to estimate precise life-cycle carbon intensities (CI) we can use fundamental engineering physics and chemistry to estimate CI. In this work, we perform a prospective life cycle assessment of a generic geologic hydrogen production and processing system. Geologic hydrogen (H2) deposits could be a source of climate friendly energy.

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