Geothermal Exploitation of natural underground water flows
To Exploit ascending underground water flow industrially for the purpose of electrical production amounts diverting this flow surfaces some to extract the maximum of possible enthalpy from it. The contribution of heat to the electrical production is appréciablement more important than the contribution of the pressure. The thermodynamic cycle is open: the collected geological fluid is reinjected on the level of the aquifers in which they would have naturally flowed (without geothermal exploitation).
The high enthalpy geothermy, based on a natural aqueous flow, consists in diverting an important enthalpy flow to convert it into electrical energy.
After extraction of the enthalpy starting from natural underground water flow, this one must be reinjected in the ground so as to disturb the least possible the natural hydrodynamics. The electrical production, in the cases of figure continued by the angiogeology, thus results from the exploitation of an open thermodynamic cycle (the same fluid is not re-used during a new cycle of electrical production). Today, almost the whole of the geothermal exploitations reinject with great depth taken underground water flow. The angiogeology recommends to reinject this flow in the aquifers close to surface which are naturally fed by this ascending underground water flow in the absence of exploitation. Diverted flow must thus be reinjected there it would have naturally ended. It is even advisable to precisely reinject the geological fluid on the level of its natural point of emergence (i.e. its entrance point in the aquifer).
The figure below illustrates the change of the temperature of an underground water flow exploited for the purpose of electrical production in accordance with the specifications of the angiogeology.
Change of the temperature in the event of geothermal exploitation of natural underground water flow
The temperature of the geological fluid decreases slightly in the well of collecting well. Geothermal energy is extracted from the geological fluid to be converted into electricity in (or them) the turbines. The geological fluid, which presents a raised mineralization, must be reinjected in the ground and not directly poured in the waterways of surface.
An exurgence point naturally gives rise to a beam of water arteries. A collecting well on the level of this exurgence point does not require necessarily a re-injection on the level of all the terminations of water artery. The re-injection can be carried out only in the fed aquifers - directly or indirectly - by a water artery “not too long” (one does not reinject to 5 km of the collecting well). To Determine the collecting locations and of re-injection optimal within the framework of a geothermal exploitation requires the control of a technique of precise positioning of ascending underground water flows, like the angiogeoscopy.
Relatively little thermal energy coming from the geothermal reservoirs is lost by dissipation within the water vessels. The water arteries do not produce any detectable thermal signal surfaces some if they lead in an aquifer (where they dissipate the key of their thermal energy).
The temperature of natural underground water flows represents one of the aspects of the collecting well of natural underground water flows; the other aspect is the pressure of these natural underground water flows.