Page 55 - Geothermal Energy Systems Exploration, Development, and Utilization

1.3 Conceptual Models of Geothermal Reservoirs 31

Geodynamic
context

Low permeability, Shallow
shallow formations Near surface systems, heat
pumps aquifers
100 °C 1 km 2 km 3 km

Low permeability, Heat, electricity? Hydrothermal
°C/100 m
deep formations reservoirs
Temperature 300 °C Hot dry Heat, electricity, hydrogen 3 km 6 km 9 km
Enhanced
5
geothermal
systems
rocks
°C/100 m °C/100 m

Supercritical reservoirs
10 2.5
Electricity, hydrogen
500 °C 5 km 10 km15 km
100 kg s −1 200 kg s −1 300 kg s −1 Depth and gradients
Water/vapor

Figure 1.17 Sketch section showing the variety of reservoirs
that can be used for heat extraction and the different uses
of the geothermal energy.

of the following four independent parameters: heat, fluid flow, permeability, and
appropriate orientation of the stress field in relation to the permeability network.
Among these parameters, only fluid flow and permeability can be enhanced
by engineering. These parameters are summarized in one sketch section that
illustrates the variety of reservoirs that can be used for heat extraction and the
various uses of the geothermal energy (Figure 1.17).
Following chapters will analyze the different processes of stimulation that
can be applied for achieving such improvement. Lessons learned from the
Soultz EGS experiment, the sustainable development of the Larderello field
in Italy, and the Icelandic geothermal power network, among other case his-
tories, show that the concept of geothermal reservoir must not be too re-
stricted. Experiences of stimulation can be realized by extending active geothermal
fields and the development of binary plants makes possible the exploitation
◦
of geothermal reservoirs with minimum temperatures of 85–100 Cfor power
generation.
A reservoir is also defined by its economic viability. Many other parameters such
as the price of the steel involved in drilling, cost of drilling depending on the