Environmental Engineering Reference
In-Depth Information
Fig. 6.3
Estimating potential
crustal heat resources.
(Armstead and Tester
1987
)
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discover viable reservoirs, which leads to high development costs and risks; another
factor is the requirement for deep reservoirs and, even when resources are accessed,
insufficient productivity and accessibility in the reservoirs. In addition, maintaining
flow rates over time presents many challenges. Moreover, hot water from geother-
mal sources may hold in solution trace amounts of toxic elements.
1
A key barrier remains the uncertainty induced by the complex and inhomoge-
neous nature of rock masses, which imposes a significant challenge to the reliable
and extensive use of geothermal resources, and requires the use of EGS, which
stimulates subsurface regions where temperatures are high enough to be utilized ef-
fectively. A reservoir consisting of a fracture network is created or enhanced to pro-
vide well-connected fluid pathways between injection and production wells. Heat is
extracted by circulating water through the reservoir in a closed loop (see next sec-
tion). This chapter thus focuses on potential approaches to reduce this uncertainty
and contribute to the development of geothermal energy extraction.
6.3
Exploitation of Geothermal Energy
A general diagram showing the penetration of surface water into zones near hot
rocks or magma and its return as hot water is shown in Fig.
6.4
(GEA
2012
). Also
see the literature (White
1967
; White et al.
1971
) for detailed discussion regarding
the characteristics of geothermal reservoirs. In order to exploit this energy, the three
necessary conditions are also shown in the Figure; namely high temperature rock,
1
Generally cooled geothermal fluids are re-injected underground which may also stimulate pro-
duction as a side benefit of reducing this environmental risk.
