Surface geochemistry: from oil and gas exploration to natural hydrogen seeps

The discovery and exploitation of the first natural (white) hydrogen reservoir in Mali has stimulated global interest in this zero-emission energy resource and carrier. Current research worldwide aims to identify its generation sources, occurrence potential, and extraction feasibility. Tools and methods normally used in hydrocarbon exploration are being adapted for this purpose. One such method is the molecular composition analysis of soil gases, a surface geochemical technique. These methods involve detecting and analyzing trace amounts of light hydrocarbons migrating from subsurface accumulations to the surface. Surface geochemical studies have been conducted across all petroleum basins in Poland. In addition to hydrocarbons, other gases, including hydrogen, were routinely analyzed in many soil gas samples. However, hydrogen played a marginal role in interpreting results aimed at identifying subsurface hydrocarbon accumulations. Large datasets containing hydrogen concentrations in soil gases, recorded over the past 35 years across Poland, remain largely unanalyzed and uninterpreted. One such dataset pertains to the Świdwin-Sławoborze area in Western Pomerania, northern Poland. In 1996, 478 soil gas samples were collected from a depth of 1.2 meters in this region. These samples were analyzed chromatographically for hydrocarbons and non-hydrocarbon gases, including hydrogen.

Molecular composition analysis revealed hydrogen in 85% of the samples, with a maximum concentration of 940 ppm. The mean hydrogen concentration (38 ppm) is five times greater than the median (8 ppm), indicating the presence of anomalous values. Hydrogen concentrations exceeding 40 ppm were partly recorded above an oil deposit located in Zechstein Main Dolomite formations. Elevated hydrogen concentrations in these samples correlate with increased levels of C₂-C₄ alkanes. Additionally, high hydrogen concentrations were observed above tectonic structures, which may indicate hydrogen migration from deeper horizons.

Reanalyzing and reinterpreting archival geochemical data with a focus on hydrogen concentration variations enables the identification of potential hydrogen migration and leakage zones at the surface. Integrating archived geochemical data with terrain morphology (e.g., potential "fairy circle" structures), geological formations, and the distribution of other resources highlights promising anomalous areas. These zones provide a valuable framework for investigating hydrogen origins and migration patterns within the Polish Zechstein Basin, part of the Central European Permian Basin.

The research project was supported by program “Excellence initiative – research university” IDUB for the AGH University of Krakow (project number 6237).