271 9. Defining high enthalpy geothermal drilling target with multi-physics 9.5 Choice of the drilling target Based on the created geological model, the conceptual model defines the hydrothermal behavior of the system. The deep high conductivity zone constitutes the heat source. The resistive body forms the geothermal reservoir with a permeability higher than that of the surrounding basaltic rocks, while the upper high conductivity zone represents the impermeable caprock. Faults and conduits could channel deep geothermal fluid near the surface and have also been taken into account with higher permeability. A parametric study was conducted by varying the permeabilities of the different objects (conduits, faults, coral barrier) as well as the heat flow. The results of the various simulations show an upward movement of hot fluid at the center of the island, controlled by the volcanic conduit or the main fault, depending on the scenarios considered (Figure 9.16). Figure 9.16 Results of the numerical simulations for two scenarios. On the left, the permeability of the magma conduits is two orders of magnitude lower than the permeability of the fault zones. On the right, the permeability of the conduits and faults is equivalent. In addition, a data assimilation study highlighted areas favorable to the presence of an underlying reservoir. This study, along with the results of numerical simulations, points to a central area of the island, between the Moya and Dziani maars, which could be a target for deep geothermal exploitation.
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