Natural hydrogen (H2) exploration is particularly focused on surface emissions (seeps) and soil-gas prospections, similar to early petroleum reservoir explorations. However, defining the amount of H2 at the surface that indicates a potentially economic resource is impossible, and identifying its origin is challenging due to the fact that geological H2 concentrations and isotopic composition can overlap with the in-situ biological signature. The potential for H2 generation in surface environments as a result of microorganisms, corrosion of iron particles or minerals, or even drilling (artificial H2) must be extensively evaluated. Despite these limitations, similarities to hydrocarbon systems suggest that certain seeps, which typically occur in correspondence with faults, are an expression of advection (not diffusion), driven by pressure gradients, and thus can disclose the existence of pressurized pools (Etiope, 2023). The fluid dynamics of gas seeps can therefore reveal the nature of the H2 supply system. Comparing seep flux rates with potential H2 generation rates, either via radiolysis or serpentinization, is a fundamental exercise for determining whether the H2 system must include a reservoir, similar to conventional natural gas systems, or if the H2 observed at the surface originates from continuous flow crossing short-term accumulations or directly from the source rock, as some scholars have hypothesized. However, analyses of the gases associated with H2 (such as CO2, CH4, N2 and He) are always advised. Assessing the potential of a geological H2 resource necessitates a holistic approach that integrates multiple geochemical, ecosystem, and geological data.
Etiope G., (2023) https://doi.org/10.1016/j.ijhydene.2022.12.025