How much natural hydrogen must be present down there?

The number of scientific articles on molecular hydrogen in the subsurface is exploding, indicating a growing interest in this potential energy resource. Various concentrations of hydrogen in naturally occurring gases and ppm values are reported, sometimes combined with projections of invoked large volumes of these gases based in part on overly optimistic assumptions. However, these figures are rarely placed into the context of a reserve estimate for an energy resource. Reserves are reliably proven quantities of raw materials that can be extracted with today's technology and at current prices. Although extraction technologies are still under development, recent cost estimates suggest that natural hydrogen may be price-competitive with hydrogen produced from renewable electricity. Nevertheless, volumetric quantities are very rarely estimated and reliably determined.

Three types of possible hydrogen deposits are predominantly discussed in the literature: accumulations over longer periods of time that could be extracted in the same way as hydrocarbon reservoirs, accumulations that are continuously replenished and source rocks that are artificially stimulated to produce hydrogen. The generation rates of H2 in the main processes, but also the reservoir properties, are crucial for assessing these possible hydrogen deposits.

We use reported gas flow rates for different geological settings and standardise these. These values are compared with reported and estimated production volumes of H2 per year that would be necessary to make a deposit economically viable. This contribution attempts to estimate the order of magnitude of a deposit that would be required for relevant, economic extraction of natural hydrogen.