Investigative research for occurrences of hydrogen, helium, methane and carbon dioxide in West Macedonia: linking geological reservoirs to subsurface gas generation and migration

<ns3:p> Background Climate change, the need for energy optimisation and higher efficiency have led to the adoption of the Paris Agreement as a response to the urge for action. The European Union has translated the aforementioned into an action framework via the Green Deal and the EU taxonomy regulation. These have initiated a series of research actions under the EU Horizon programme. Part of this research is based on carbon dioxide capture and geological storage, such as the Pilot Strategy, and hydrogen storage, such as the HyStorIES, both Horizon 2020 project. A focused hydrogeochemical survey as part of a larger mapping survey was conducted in West Macedonia to identify a potentially suitable location for gas reservoirs, gas sources and gas migration routes based on previous research. Gases investigated were hydrogen, helium, methane and carbon dioxide. The study involved isotopes to identify the source of gases and thus provide clues for generation and migration routes. Methods The investigation presented in this study deployed sequential spring and borehole water sampling for geochemical analysis of trace elements and gas analysis for hydrogen, helium, methane and carbon dioxide to identify and characterise gaseous geological reservoirs. The investigation extended into isotope studies for d <ns3:sup>13</ns3:sup> C <ns3:sub>TDC</ns3:sub> , d <ns3:sup>13</ns3:sup> C <ns3:sub>CH4</ns3:sub> , dD <ns3:sub>CH4</ns3:sub> , δD <ns3:sub>H20</ns3:sub> , δ <ns3:sup>18</ns3:sup> Ο <ns3:sub>Η2Ο</ns3:sub> . Results The analysis provided evidence for the existence of helium, biogenic methane, carbon dioxide and traces of hydrogen that need to be further investigated for validation and better understanding of the gas generation and migration routes. Conclusions The data suggests the existence of helium, methane, carbon dioxide and validated trace concentrations of hydrogen from previous studies in the wider area. Isotopic analysis provides strong evidence for biotic generation of methane, whereas helium comes from a deeper source. This preliminary investigation indicates the existence of multiple gas generation and migration mechanisms and paves the way for further research. </ns3:p>