Geoffrey Ellis

The availability of accurate national and regional-scale maps of prospective areas for geologic hydrogen resources is invaluable to the energy industry as a guide for exploration activities. Knowledge of the potential distribution of geologic hydrogen resources is also critical for policymakers at the federal, state, and local levels. Geologic hydrogen resources likely occur in places that historically have not experienced natural resource extraction. To gain societal acceptance, the development of any discovered resources will need to be done responsibly. If not already in place, appropriate regulations to protect environmental health and ensure safety will need to be enacted. Furthermore, understanding the distribution of potential resources is essential for the decision-making process for infrastructure development. Previous efforts to assess prospectivity for geologic hydrogen resources have been limited in the spatial scale and/or the extent to which contributing factors are accounted for. To address this need, the U.S. Geological Survey has developed a methodology for determining the relative prospectivity of geologic hydrogen resources. This method has been applied to the onshore regions of the conterminous United States. The approach is based on a conceptual geologic hydrogen system model, analogous to the petroleum system, comprising sources, migration pathways, reservoirs, traps, and seals, as well as consideration for preservation of geologic hydrogen accumulations. Geologic, geochemical, and geophysical datasets were identified as proxies for the essential components that are required for an effective geologic hydrogen system. Individual input data sets were assigned weightings (i.e., chance of success) derived from interpretations of published literature and then integrated to determine net prospectivity for specific regions. The integration methodology was primarily based on geologic inference. Given our nascent understanding of the geologic hydrogen system model and the limited amount of data that are available from known accumulations, there is a high degree of uncertainty associated with the model and the significance of the input data. This uncertainty is accounted for by employing a range of weightings for each of the model inputs and then applying a Monte Carlo approach to calculate probabilistic distributions for prospectivity values. Accounting for the three-dimensional nature of geologic hydrogen accumulation potential when mapping in two dimensions remains a challenge. Maps of discrete prospectivity probabilities (e.g., P10, P50, P90, etc.) have been produced. The results indicate that areas of known ultramafic and radiogenic hydrogen source rocks are highly prospective, but the potential for effective reservoirs, traps, and seals also substantially impacts resource prospectivity. The resultant maps will be available to the public in an interactive, online format, which allows for an in-depth examination of the controls on geologic hydrogen accumulation potential but emphasizes the high degree of uncertainty. This effort represents the first attempt to assess geologic hydrogen resource prospectivity at the national scale using a holistic geologic approach. The details of the methodology will also be made available and can readily be applied to other locations at broader (e.g., international) and more local (e.g., regional) scales.Co-authors : Sarah E. Gelman, Jane S. Hearon, Robert F. Miller, Scott A. Kinney, and Christopher C. Skinner