A new geothermal exploration workflow for deep sedimentary basins and basement

Chrystel Dezayes (1)

1 BRGM - Bureau de Recherches Géologiques et Minières (BRGM)

In order to expand the geothermal energy exploitation, we need to explore various geological contexts, particularly the sedimentary basins, which concentrate many customers. Nowadays, with the improvement of the binary power plant productivities and the need of industrial heat, the deep layers of sedimentary basins and the upper part of the basement are attractive to tap fluid with temperature between 120°C and 150°C. In a normal geothermal gradient (around 30°C/km) context, this temperature range is reached between 3 and 5 km depth and corresponds to the deep layers of sedimentary basins (aquifers more or less permeable, namely HSA) and the upper part of the basement, more or less fractured and altered, having potentially used EGS technologies. In such complex and diverse geological setting, we propose to set up and validate an integrated and scale-dependent exploration workflow that consists in building, step by step, more and more refined subsurface models based on larger scale models To achieve this, three questions arise:-What are we looking for? What are the key parameters and the key situations favorable for geothermal heat/fluid extraction? In order to optimize the exploitation, the three essential parameters to know are obviously temperature (the highest at the shallowest depth), the natural permeability (both from porosity and fractures), and the presence of brines and recharge waters. These key parameters are related to the geological patterns and subsurface phenomena, which are called key situations and constrain spatially the favorable areas.-Which methods are able to identify these key situations at the different scales? Standard exploration methods (e.g. active/passive seismics, electromagnetics, geothermometry and geology) have been tested on the specific case of basement and deep sedimentary layers to validate which techniques are relevant to identify key situations. Whereas some of these can be very capital-intensive (e.g. active seismics), the economic benefit to the project through its geological risk reduction can easily compensate for the upfront investment.

Domaines: Géologie appliquée

Chrystel Dezayes. A new geothermal exploration workflow for deep sedimentary basins and basement. European Geothermal Congress - EGC 2019, Jun 2019, La Haye, Netherlands. ⟨hal-01870398⟩