| Title | The Key role of first-order geological paradigm in deep geothermal exploration |
|---|---|
| Authors | Bellanger, M; Auxiètre, J-L; Ars, J-M; Hautot, S; Tarits, P |
| Year | 2016 |
| Conference | European Geothermal Congress |
| Keywords | geological paradigm, deep geothermal exploration |
| Abstract | The approach of TLS-Geothermics for deep geothermal exploration is based on two axes of research. The first one, which is also the first step, is the development of the first-order geological knowledge (developed here). The second one concerns technological development for local physicochemical characterisation (static to dynamic) in three dimensions and involves a geological model coupled to geophysical measurements and numerical modelling. These axes are presently tested on two high temperature projects supported by TLS Geothermics in the French Massif Central. TLS Geothermics defines the intrinsic problematic of deep geothermal exploration as targeting a natural drain where circulate hot fluids. To solve this, it appears essential to combine its induced problematics. The result of this approach is that first-order geological paradigm is a key parameter to improve a solution which leads to drastically reduce the geological and drilling risks. As the deep evolutions of the crystalline structures are poorly constrained due to a lack of deep well in this geological environment (typically deeper than 0.5 to 1km), it results that various paradigms can explain the geodynamic evolution of the Variscan belt. These paradigms involve highly contrasted features at depth, features which have first-order controls on the physicochemical properties of the drains and reservoirs, in terms of ability for the fluid flows and heat transfers. Actual paradigms about the Variscan dynamic of magmatism perfectly illustrates this purpose. The first paradigm involves a plutonic emplacement as a ‘bubble’ of granitic melt which moves upward into the ductile crust (diapiric intrusion) and which is stopped to the base of the brittle crust under which it can be spread to form a laccolith. The melt could also join the surface using newly formed or inherited faults and fractures of the brittle crust. This dynamic leads to drawn the magmatic bodies as isolated within the nappe stack.Another paradigm, less common in literature, involve the plutonic emplacement as the model of Core Complex. This last one is argued here. We demonstrate how it has a significant impact on crustal cross-sections and so on the crustal interfaces (structural and rheological) which could drive fluids flow and heat transfers. The drastic differences in the crustal conception which use various geological paradigm (but similar data), do of this one a first-order key parameter to constraint crustal fluids flow and heat transfers, critical for the deep geothermal purpose. |