Geothermal Energy and Structural Geology

Structural geology has a long tradition of applications and developments in the field of energy resources. From the balanced and restored cross-sections first used in hydrocarbon exploration, to fracture analysis aimed at reservoir characterization and the modelling of fluid flow, major advances and new fundamental techniques in structural geology developed over the decades are tightly coupled with the energy industry. Within the framework of the current energy transition, the focus has moved towards renewable energies such as geothermal energy. Geothermal plays are strongly influenced by both the regional tectonic regime and local structural setting. The former involves fundamental parameters such as the heat flow, hydrogeological regimes and fluid chemistry, which are closely related to the geodynamic setting (convergent or divergent plate boundaries, intracontinental rifts, stable cratonic regions, etc.). At a more local scale, a complex combination of various environmental factors determines the suitability of an area for producing geothermal energy. A geothermal resource is, in fact, part of a natural system in which geological characteristics including the rock type, diagenesis, mechanical behaviour of the rocks and active stress field, in addition to the parameters mentioned above, influence key features such as the occurrence and spatial distribution of domains characterised by high porosity and high permeability (and related fluid circulation), vertical and lateral temperature gradients, and reservoir behaviour during injection and production, which, in turn, are crucial for power plant efficiency. Particularly in rocks characterized by low primary porosity and permeability, the geothermal system permeability is mainly determined by the fracture aperture and connectivity. As fault zones and fracture networks represent the main pathways for fluids, obtaining quantitative fracture attributes and carrying out discrete fracture network (DFN) modelling are fundamental for performing fluid flow simulations and, where necessary, proposing reservoir stimulations (e.g., hydraulic fracturing). In summary, a multiscale, comprehensive picture of the geological setting and structural architecture of a potential geothermal site is fundamental for any site-specific, appropriate field development. Therefore, a prior geothermal suitability assessment is fundamental. This is commonly based on a series of exploration techniques often involving invasive inspections (e.g., well drilling), high costs and the need for legal permissions.