Geological characterization of the “Fonts-Bouillants” helium discovery - France

Geological characterization of the “Fonts-Bouillants” helium discovery - FranceRussier E1,2, Géraud Y2, Hauville B1, Tarantola A2 ,Beccaletto L3 and Diraison M11 45-8 ENERGY, France2 GeoRessources, University of Lorraine, France3 BRGM, F-45060, Orléans, France ABSTRACTHelium is essential for the manufacturing of many of our daily commodities such as optical fibres, computers or cell phones (semiconductors and processors), medical use (MRI scanners) or in other more specific applications such as airlifts, leak detection, gas chromatography or diving. Nowadays, Europe imports 100% of its helium needs from overseas and is facing regular shortages, reason why 45-8 Energy embarked five years ago on helium exploration and production in Europe. Helium is a noble gas mostly coming from the natural radioactive decay of Uranium and Thorium contained in the crust and the basement. Its migration and accumulation are strongly linked to a vector fluid that can be CO2, N2, CH4 or water. Helium and its vector fluids are then trapped and sealed in a rock reservoir. The Fonts-Bouillants area is located at the southern edge of the Paris Basin at the vicinity of the French Massif Central and Limagne rift. The 45-8 Energy project aims to jointly produce He and CO2 from a gas which is naturally seeping through the major Saint-Parize fault (SPF).  Geological origin and migration pathway of He are therefore key questions to define the exploration guide, in particular to locate production wells to produce the seeping gas and process it. A multidisciplinary approach involving geology, geophysics, petrophysics and geochemistry has therefore been deployed. Because geological context was hardly documented in this area, a wide range of geophysical data were acquired or reprocessed and coupled with field geology to build a regional geological model. The initial geological model was considerably updated and a hidden and thick Late Palaeozoic depocenter was especially highlighted below the Mesozoic series. Well data in nearby analogous basins as well as outcrops enabled rock collections to conduct petrophysical and geochemical characterization. The main reservoirs discovered currently are in Triassic and Jurassic sandstones, and fault like Saint-Parize fault acted as barrier and drain. Our outcrops petrophysical and geochemical study highlight the importance of Late Palaeozoic basin for the helium system:As a potential rock source, with higher U-Th concentrations (3-13.5, 8-24 ppm) than typical crustal U-Th concentrations (1.8 and 7.2 ppm, [1]). As a potential migration pathway and reservoir, with sandstones and conglomerates porosity higher than 20% and permeability higher than 100 mD.  Finally, gas sampling was performed in local natural springs, but also during well testing conducted in shallow boreholes which have encountered gas bearing reservoirs in the Mesozoic along the SPF. Helium generation system was modelled with geochemical data from the rocks and the fluids and from the volumetric capacity of the Palaeozoic basin. Keywords: Helium exploration, Geophysics, Petrophysics, GeochemistryThemes: Helium exploration References:[1] Krauskopf, K. B., & Bird, D. K. (1967). Introduction to geochemistry (Vol. 721). McGraw-Hill New York.