English: This image describes using general examples the principal types of geothermal industrial sources:

- Hydrothermal systems (conventional sources). the source is found at non-extreme depths (from a few hundred metres up to around 2000 m) in areas with strong thermal anomalies, and consists of a reservoir rock fed laterally by meteoric water percolating from the surface and characterised internally by water circulation by convection.

Unconventional sources, namely: - Geopressured systems. Confined aquifers at depths of over 2000 m with the presence of anomalous pressures. - Magmatic source systems. Adjacent to active volcanic systems with a shallow magma chamber or hypoabyssal intrusive bodies (within 5-6 km), in which the liquid used for heat extraction is heated directly from the roof of the magmatic intrusive body. - Hot brine systems. These systems can form either within aquifers in which there is a progressive concentration of salts originally contained in the reservoir water through convection and gradual dispersion of the fluid phase over very long periods of time, or in particular structural and depositional contexts that bring the reservoir rock into contact with saline diapirs. - Supercritical systems. The source is located at greater depths (3000-10000 m) and the water contained therein is at high pressures (from a few hundred up to around 1000 atm) and temperatures up to a few hundred degrees, and can therefore reach the supercritical state, with a very high energy concentration that is higher than that of hydrothermal systems, even those with dominant steam.

- Petrothermal systems. the heat source in this case consists of anhydrous rocks and high temperature with negligible primary porosity and permeability, which therefore require stimulation techniques (hydraulic fracturing and water injection) to produce fluids. This type of development is called EGS or Enhanced Geothermal Systems.

English: This image describes using general examples the principal types of geothermal industrial sources: - Hydrothermal systems (conventional sources). the source is found at non-extreme depths (from a few hundred metres up to around 2000 m) in areas with strong thermal anomalies, and consists of a reservoir rock fed laterally by meteoric water percolating from the surface and characterised internally by water circulation by convection. Unconventional sources, namely: - Geopressured systems. Confined aquifers at depths of over 2000 m with the presence of anomalous pressures. - Magmatic source systems. Adjacent to active volcanic systems with a shallow magma chamber or hypoabyssal intrusive bodies (within 5-6 km), in which the liquid used for heat extraction is heated directly from the roof of the magmatic intrusive body. - Hot brine systems. These systems can form either within aquifers in which there is a progressive concentration of salts originally contained in the reservoir water through convection and gradual dispersion of the fluid phase over very long periods of time, or in particular structural and depositional contexts that bring the reservoir rock into contact with saline diapirs. - Supercritical systems. The source is located at greater depths (3000-10000 m) and the water contained therein is at high pressures (from a few hundred up to around 1000 atm) and temperatures up to a few hundred degrees, and can therefore reach the supercritical state, with a very high energy concentration that is higher than that of hydrothermal systems, even those with dominant steam. - Petrothermal systems. the heat source in this case consists of anhydrous rocks and high temperature with negligible primary porosity and permeability, which therefore require stimulation techniques (hydraulic fracturing and water injection) to produce fluids. This type of development is called EGS or Enhanced Geothermal Systems.