Hydrogen (H2) targeting in orogenic belts and foreland basins: the Pyrenean belt (SW France) as a case study
Abstract
Natural hydrogen (H2) seepages may represent a new promising source of energy for a low carbon society. Numerous geological evidences of natural H2 seepages and accumulation are now well identified, but our knowledge of hydrogen behavior in the crust is so limited that it is not yet possible to consider exploitation of this resource. To date, there is neither exploration strategy nor any resource assessment, as practical guidelines for hydrogen targeting are missing. Here, we lay the foundation of a new targeting approach dedicated to H2 exploration, using the Pyrenean orogenic belt and its northern foreland basin as a playground. This latter geological setting represents a promising framework to investigate a potential H2 system, as all the conditions for H2 generation, migration/drainage, and entrapment are gathered. First, geophysical data indicate the presence of a massive mantle body at shallow crustal level (< 10 km depth) below the foreland basin. Second, the occurrence of several serpentinized lherzolite massifs (hydrothermal alteration process known to produce H2) along main structures demonstrate that H2 was and can probably still be produce. Third, the architecture of the Pyrenean belt brings the required conditions for deep gas drainage (major faults deeply rooted in the crust) and entrapment, as demonstrated by the presence of gas tight sedimentary covers (clays and marls) allowing the formation of large gas fields (e.g., the giant natural gas field of Lacq).
Thanks to a preliminary surface survey of H2 natural seepages, and using the above mentioned geological features as a prospecting guide, we discover the first H2 anomalies. In-situ gas measurements record high H2 concentration along two main faults located in the foreland basin. More than 6000 ppmv of H2 have been measured in these two latter locations. It appears that mapping H2 concentration anomaly in soils and outcropping rock formations at different scales is already extremely instructive when superimposed to geological, seismic, and gravimetric data. H2 flux measurements are currently being carried out in these discovered hot spots. Soil microbiology, H, C, O isotope signatures in the exhaled gas (H2, CO2 and CH4) and noble gas measurements are also performed to better constrain the source of H2 and gain insight into this potential energy resource.- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2019
- Bibcode:
- 2019AGUFM.H51J1615L
- Keywords:
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- 3305 Climate change and variability;
- ATMOSPHERIC PROCESSES;
- 1803 Anthropogenic effects;
- HYDROLOGY;
- 1829 Groundwater hydrology;
- HYDROLOGY;
- 1875 Vadose zone;
- HYDROLOGY