| Abstract |
One of the main objective of the MEET project is to gain further knowledge on geothermal systems embedded in sedimentary basins. It intends to explore the feasibility of electricity and/or thermal energy production using petroleum sedimentary basins (Dalmais et al., 2020). The Triassic formations of the Paris Basin present a good geothermal potential with their 80-125°C reservoir temperature, making them excellent candidates for energy co-production. In order to explore such opportunity, several aspects are investigated to provide an in-depth knowledge of the Triassic formations: (1) Establish a robust sedimentological frame and diagenetic history of the Triassic sandstone and dolomite reservoirs. (2) Highlight potential reservoirs using rock physics properties (porosity, permeability...). (3) Combine those characteristics and properties into the regional stratigraphic framework of the Paris Basin, providing a better understanding of the Triassic formations at a larger scale. The comprehension of the geothermal prospects within Triassic formations implies to evaluate the degree of horizontal and vertical connectivity between the reservoir levels. To achieve this, the procedure is based on several phases. Firstly, the sandstone bodies are characterized by their facies from a core study and the determination of facies associations. Secondly, the electrofacies determination is realized by a well-log analysis. Thirdly, the combined facies and electofacies analysis leads to define the vertical evolution of depositional environment for each well. Finally, the correlations of the depositional environment evolution at different scales allows defining sequence boundaries and stratigraphic sequences for the Upper Triassic succession. The post-depositional processes of the Triassic sandstones are characterized separately. Indeed, diagenetic processes like silicification or dolomitization of sandstones induced by soil formation and fluid circulations in vadose or aquifer zones are studied through sedimentary petrography (optical microscopy, cathodoluminescence, SEM), so that their impacts on reservoir quality are evaluated. Regarding the petrophysical input, new sets of properties are characterized for key horizons that represent a good flow potential identified in hydrocarbon exploration. The porosity, permeability, P/S wave velocity and electric velocity, as well as the respective anisotropies of these horizons are analysed for each reservoir. The evaluation of the degree of anisotropy in space allows depicting variations of the petrophysical parameters in relationship with sedimentary and diagenetic processes. The different anisotropies inform about the secondary porosity network currently observed and the most transmissive pathways for geothermal fluids. To extent further the analysis, a comparison between fine measurements at plug scale and well-log signals is performed. This allows understanding whether the physical parameters measured on samples can be used to better correlate facies types using well logging, or as proxies for fluid control and amount of circulation, within the reservoir and for non-cored sections. Along with the study of subsurface data in the Paris basin, an analogue formation of Triassic sequence is chosen in Ardèche (France), where a sedimentary system of fluvio-lacustrine continental environment accumulated along a former passive margin of the Tethys Ocean. Sedimentary features are described along several sections for sequence stratigraphy and rock physics properties are analysed from samples collected on various lithologies of these sections. Besides, deep research boreholes drilled in the tilted blocks of the margin provides material to investigate these relationships locally and for the geothermal exploration settings of the Paris Basin. The dual settings of the Paris basin and its facies analogue in Ardèche is a unique occasion to understand the vertical stacking and horizontal continuities of sandstones and dolomites, for both in-situ and exposure conditions. This approach would bring insights on the capacity of Triassic deposits to bear new geothermal prospects associated with previous oil fields. References Dalmais, E., Genter, A., Trullenque, G., Leoutre, E., Leiss, B., Mintsa, A.-C., Rajsl, I., Marot, M. (2020) MEET project: toward large scale deployment of deep geothermal energy in Europe. Proceedings of the World Geothermal Congress 2020 – Reykjavik. |