Geothermal handbook: PlanninG and Financing power Generation t e c h n I c a L r e p o r t 2 / 2

convective fracture controlled systems
the heat source is the hot crust at depth in
tectonically active areas, with above average heat flow. Here geothermal water has
circulated to considerable depth (> 1 km), mostly through vertical fractures, to “mine” the heat
from the rocks. 
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Sedimentary geothermal systems
are found in many of the world’s major sedimentary
basins. These systems owe their existence to the occurrence of permeable sedimentary
layers at great depths (> 1 km) and above average geothermal gradients (> 30º C/km).
These systems are conductive in nature rather than convective, even though fractures and
faults play a role in some cases. Some convective systems (such as convective fracture
controlled systems) may, however, be embedded in sedimentary rocks (Figure 1.5).
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