Page 304 - Geothermal Energy Systems Exploration, Development, and Utilization

280 5 Geothermal Reservoir Simulation
Z
Stimulated reservoir Fracture network Y North
RH11 −2000 −2000 X East
Borehole locations RH12 −2050 −2050

z (Depth below surface) (m) z (Depth below surface) (m)
−2100
−2100
RH15 −2150 −2150
−2200 −2200
−2250 −2250
−2300 −2300
−2350 −2350
−2400 −2400
−2450 −2450
−2500 −2500
350
350
300
300
−400 −375 −350 −325 −400 −375 −350 −325 250
250
x (east) (m) x (east) (m)
Figure 5.24 Rosemanowes geothermal reservoir model (Kolditz and Clauser, 1998).
porosity. Since normal and shear forces are acting on the fracture surfaces, the
hydraulic characteristics of the fracture network are strongly affected by the in situ
tectonic stress field, as well as in the tectonic stress field; therefore, anisotropy
is observed in the hydraulic behavior of the fractured reservoir. A model with an
anisotropy factor of b1/b2 = 5 (ratio of apertures of the two fracture sets) and with
matrix porosity of about 1% provides the best fit to the data (Figure 5.25). The results
of this hybrid fracture-matrix model are compared with earlier findings based on a
parallel fracture array model by Nicol and Robinson (1990) and a stochastic fracture
network model by Bruel (1995a). More details of the Rosemanowes geothermal
reservoir model can be found in Kolditz and Clauser (1998). Hydromechanical
coupling effects have been not yet investigated in these studies.

5.8
Soultz-sous-Forets (France)

In order to simulate the hydraulic behavior of HDR reservoirs, basic flow processes
in fractured rock needs to be understood. Fractured rocks are strongly hetero-
geneous media. They consists of different structural components such as matrix
blocks and fractures with varying orientations as well as different length scales.
Owing to their geometric complexity several conceptual models were developed in