Page 255 - Geothermal Energy Systems Exploration, Development, and Utilization

4.10 Case Studies 231
3500

3550
In equilibrium
(GGA, 24.09.03)
3600

3650
Solling

3700
Depth (m) 3750

Detfurth
3800

13.07.04
3850

3900
Volpriehausen
3950

4000
130 140 150 160
Temperature (°C)
Figure 4.25 Temperature profile recorded half a year after
fracturing the Detfurth-sandstone (black) in comparison to
the equilibrium profile (red).
of pressure. Formation linear flow from a high conductive fracture into the matrix
can unambiguously be derived from these characteristics.
Because of the long-lasting formation linear flow, a radial flow regime has not
been observed and the independent determination of the matrix permeability is
not possible. Assuming an effective matrix permeability of 1 mD, a fracture area
2
of 10 000 m can be derived. For an assumed permeability of 0.1 mD the fracture
2
area would be approximately threefold higher (30 000 m ). The persisting fracture
area is significantly smaller than the fracture area during stimulation.
The most important result is, however, that a large part of the fracture remains
open (infinite conductive) even at low pressure. It demonstrates that the concept of
massive waterfracturing without proppants is a successful method for stimulating
low permeable siliciclastic sedimentary rock.