Abstract. Geothermal energy is an important and sustainable resource that has more potential than is currently utilized. Whether or not a deep geothermal resource can be exploited, depends on, besides temperature, mostly the utilizable reservoir volume over time, which in turn largely depends on petrophysical parameters. We show, using a large series (n = 1027) of 4-dimensional finite element models of a simple geothermal doublet, that the lifetime of a reservoir is a complex function of its geological parameters, their heterogeneity, and the background hydraulic gradient (BHG). In our models, we test the effects of porosity, permeability, and BHG in an isotropic medium. Further, we simulate the effect of permeability contrast and anisotropy induced by layering, fractures, and a fault. We quantify the lifetime of the reservoir by measuring the time to thermal breakthrough, i.e., how many years pass before the 100 °C isotherm (HDI) reaches the production well. Our results attest to the positive effect of high porosity; however, high permeability and BHG can combine to outperform the former. Certain configurations of all the parameters can cause either early thermal breakthrough or extreme longevity of the reservoir. For example, the presence of high permeability fractures, e.g., in a fault damage zone, can provide initially high yields, but channels fluid flow and therefore dramatically restricts the exploitable reservoir volume. We demonstrate that the magnitude and orientation of the BHG, provided permeability is sufficiently high, are prime parameters that affect the lifetime of a reservoir. Our numerical experiments show also that BHGs (low and high) can be outperformed by comparatively small variations in permeability contrast (103) and fracture-induced permeability anisotropy (101) that thus strongly affect the performance of geothermal reservoirs.
QUANTITATIVE ANALYSIS OF DEFORMATION ALONG THE FAULT DAMAGE ZONE OF THE KLIMATIA THRUST (NW GREECE, IONIAN ZONE)
