Petrographic and Petrophysical Study of Metamorphic and Crystalline Rocks beneath the Paris Basin for Geothermal Potential
Basement cores retrieved from the Variscan belt under Paris Basin are studied in order to understand in-situ rock properties and petrographical characteristics of deep potential reservoirs. Within the frame of the European MEET project (Dalmais et al., 2020), core logging is performed on schists, gneisses and quartzites to identify structural patterns and particular mineralogical occurrences in relationship with structures such as veins or faults and fractures. In addition, plugs are analyzed
... order to quantify physical properties (porosity, permeability, P/S wave and electric velocities, ASM and their anisotropies) to characterize rock types and reservoir capacities for a possible geothermal resource underneath the basin. In the scope of this work, the analytical approach integrates three mains aspects: - The core logging reveals the evolution in the rock type, which gives clues about the emplacement of metamorphic units. To complement these observations, the presence of mains structures, fractures and cleavages allow relating the structural units to a tectonic sketch and providing potential pathways for fluid circulation. - Thin-section are examined for detailed mineralogical characterization under Optical Microscopy, SEM, and Raman spectroscopy. These types of analysis give indications about the processes leading to precipitation and possibly the nature of paleo-fluids. - Plug samples from the drill cores are analyzed for various rock physics properties that help us to understand the distribution of porosity/permeability and their anisotropy in the different kinds of basements medium. This step is treated in a second time and is not part of this paper. While the investigation of deep Variscan rocks for geothermal exploration is realized, a complementary approach on the overlying Triassic deposits is also led in the European MEET project (Sengelen et al., 2020), showing that the Paris basin could count on several potential reservoirs in order to diversify its geothermal resource.