Page 76 - Geothermal Energy Systems Exploration, Development, and Utilization

52 2 Exploration Methods
Volcanic rock
slip tendency and seismicity GtGrSk4/05
t/s
Slip tendency plot n
s 0.456
N 2
0.410 N18E
0.365 F28
0.319 Sandstone layers
18/50 0.273 51SE
s 0.228
W 1 E
0.182
s 3 0.137 Volcanic rock
0.091
0.046
0.000
S
Normal fault pole Seismic events EGrSk3/90
Normal slip vector
(a) (b)
Figure 2.5 (a) Slip tendency plot of the together with least-square fitted plane (trans-
lower Permian volcanic rocks in the Groß parent yellow). The distribution of seismicity
Sch¨ onebeck field. The pole of plane repre- fits the orientation of the F28 fault plane
sents the mean plane as derived from mi- within the reservoir (Moeck, Kwiatek, and
croseismicity. (b) Mean plane of recorded Zimmermann, in press). (Please find a color
seismic events together with a spatial distri- version of this figure on the color plates.)
bution of recorded seismicity (yellow boxes)
subsurface data is therefore not only the initial step in any geothermal investigation
but also a crucial aspect of any EGS project.

2.4
Geophysics

Geophysical methods have played a key role in geothermal exploration for many
years. Specific exploration techniques and their possible combinations for EGS
applications are not well established yet, because the parameters searched for a
profitable utilization are not only the physical parameters of the geothermal system
itself but additionally information on the condition of the reservoir (e.g., stress,
strain, and (pore-) pressure) that have to be derived from the surface.
The geophysical methods are usually aimed at yielding information about a
possible geothermal reservoir, the heat source, and the hydraulic situation. In
the case of exploration for possible EGS applications, the methods used should
additionally help to obtain precise information about structural and tectonic setting,
regional and local stress field, and many other parameters in a depth range up to
several kilometers, which are critical for later stimulation procedures.
Therefore, in this chapter, today’s most prominent geophysical exploration
methods are outlined together with remarks on possible developments toward
specific EGS exploration methodologies. These, of course, have to be most closely
linked to geological, geochemical, and geophysical well logging information as well
as to rock physics from laboratory experiments.