Why shouldn't the improved geothermal systems (SGA) be a first choice?
The improved geothermal systems (SGA) are, at best, an experimental makeshift, with worse, a risk for the company. They do not offer any advantage on a geothermal exploitation founded on data and an approach exits of the angiogeology. Thanks to the feedings of this one, their justification and their raison d'être disappear.
Because of difficulty in locating with precision the geothermal reservoirs by means of technologies which were available on the market before the angiogeoscopy, much of companies tried out other techniques of recovery of heat present in the deep layers of the ground (i.e. to several thousands of meters under ground). The improved geothermal systems (EGS in French or EGS or “Geothermal Enhanced English Systems”) do not require the presence of water reservoirs with high enthalpy. Aqueous flows of heat exchange are injected starting from surface in hot, dry and necessarily permeable rocks to be recovered on the surface in order to extract captured heat from it. An alternative denomination is geothermics of the hot and dry rocks (HDR or “Hot Dry Martini Rock'n'rolls” in English). These systems of anything “are not improved”, they compensate, by an artefact expensive and risked injection with great depth, the incapacity to locate the optimal geothermal reservoirs and their collecting locations.
Such “improved” systems known as are, at best, of the makeshifts in the absence of possibilities conferred by the angiogeology, at worst of the very serious risks for the perenniality of the production of energy of geothermal origin. That one thinks only one moment of what would occur if such an “improved” exploitation known as were to be marked to be the cause of an earthquake.
Because of omnipresence proven by the angiogeology of the geothermal reservoirs on the surface of the ground, the importance of their efferent flow and the precision with which their optimal collecting locations can now be localised thanks to the angiogeoscopy, the justification of such improved geothermal systems disappears. The table below presents a short outline of their disadvantages compared to what natural aqueous a flow exploitation resulting from geothermal reservoirs offers.
| Weaknesses of the improved geothermal systems | Why, and up to what point, these points are weaknesses | Corresponding Situation met in angiogeology |
|---|---|---|
| Permeability difficult to guarantee and maintain | The temperature increases with the depth, while the permeability of the rocks, it, decreases with the depth. Without a satisfactory permeability, not of improved geothermal systems. The permeability can be increased by injecting water under very strong pressure to induce cracks, but:
| The permeability of the crossed layers is not a concern for the angiogeology. Nature was responsible for the way of the water arteries and it is their origin (their meeting on the level of the geothermal reservoirs) which interests us and which can be precisely localised by angiogeoscopy. |
| Drilling depth | To reach temperatures of sufficient rock, drillings must be made on several thousands of meters (typically from 3,000 to 5,000 meters). The more important the depth is, the more the costs and the technological challenges are important. | Most drillings recommended by the angiogeology is located at depths between 800 and 1,500 meters (thus completely within reach of a current technology). |
| Risks of induced seismicity | These risks are real and significant. They result from the artificial cracking of the rocks (induced by forced injections of fluid) and effect of those on the lithic tensions. The lithic structures are frequently in an unstable state of balance. That means that a weak deterioration of their profiles of compression is likely to cause an important readjustment, therefore to cause an earthquake which would be accompanied by appreciable damage - and perhaps also of human losses. Even if it daily occurs earthquakes near such sites, those are not felt by the population. This does not exclude that a serious earthquake can produce. Moreover, the water injection under very strong pressure lubricates also the contact between plates and makes them thus more likely to slip one compared to the other with, again, an earthquake for potential consequence. The supervening of a serious earthquake would very seriously compromise the future of all the improved geothermal systems and would fade inevitably on the credibility of natural aqueous the flow exploitations resulting from geothermal reservoirs, as preached by the angiogeology. Even if the probability of occurrence of such an event is weak, its impact would be enormous, returning, today, the disproportionate risk with the benefit which one can draw from the EGS. | Reduced to the minimum, because the collecting well and the possible re-injections (in the event of geothermal exploitation) are done at the places which disturb less hydrodynamic balance (the collecting wells and re-injections are done with leakage points and of existing feeding since millenia). |
| Pollution of the sheets | The fracturing of the rocks very requires the injection of fluids under high pressure and especially nouveau riches by corrosive chemical components. These toxic components end up being found in the aquifers and make them definitively unsuitable to consumption. | No injection of fluid polluting is necessary during the exploitation of a site specified on the basis of angiogeology. |
| Poor Yield | The output of such systems is reduced considerably by:
| The geological fluid taken on the level of the leakage point of water reservoirs goes back naturally to surface. The injection wells can be made at a shallow depth (a few tens of meters) if one takes account of the angiogeological complexing of the site. |
| Heavy Maintenance | To Maintain a permeability sufficient requires frequent re-injections to fracture the rocks and, when such re-injections become inoperative, the drilling of new wells. | Maintenance is minimal and without common measurement with the EGS. |
| Bulk-heading of the zones of re-injection | To avoid too important losses of the reinjected fluids, the zones of re-injection are partitioned by various techniques. These techniques are today only at one experimental stage (no matter what their suppliers say some). The maintenance in the time of these artificial separations, under conditions of raised pressure, is far from being assured (try to negotiate a guarantee of their maintenance in time). In Addition To these uncertainties stability in time, these techniques are very expensive. | The collecting well of water bearing sites on angiogeological basis does not require any artificial bulk-heading of the zone of collecting well. Moreover, we offer exceptional guarantees spontaneously. |
| Data-processing Models | The necessary data-processing models to reproduce the behaviors inside the artificial reservoirs are extremely complex and not yet available. They will not be it before the next decade (in the best of the cases). These models, said, THMC, must reproduce the interaction between the aspects thermal, hydrodynamic, mechanical and chemical. Moreover, these models are useful only if they are fed by surveys of precise and complete drilling (from the point of view of the measured data and covered space). | The hydrodynamic models of dispersion of the geological fluids in the form of water vessels, today, perfectly are controlled and effectively complémentent the surveys of ground by angiogeoscopy. |
| Reinjected Fluid | Such an exploitation can indeed choose the fluid injected to capture the heat of the rocks. What can appear as an advantage is in fact a disadvantage, because it is necessary to have a sufficient aqueous feeding to carry out such an injection whose fraction only is recovered. | An exploitation based on the principles of the angiogeology does not have obviously the choice of the geological fluid. If this one were to prove to be inadequate for a profitable exploitation (because too much corrosive, or too charged out of non condensablees gas, or containing too many particles), there remains always the option to seek another locus of exploitation. |
| Investment costs and of exploitation | These costs are directly function:
In these three connections, the costs of the EGS are very significantly higher than those associated with an exploitation site based on data and an approach in conformity with the angiogeology. | Optimal compared to the geothermal potential offered by the site. |
Conclusion
We cannot think of only one advantage which the systems geothermal known as improved (or EGS would offer) on what currently the angiogeology allows. Their raison d'être is founded at the same time on an ignorance of hydrogeological reality and the incapacity of the companies which market these techniques to locate underground water flows precisely. Now that this ignorance is raised by the angiogeology and that the angiogeoscopy makes it possible to locate underground water flows very precisely, these systems should disappear, because they present too much risks and more any advantage (if it is not the merit - for some - to exist).