Geophysical Concepts, Applications and Limitations

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Slide 7

Origins of geothermal energy

1. Left-over heat from the time of the accretion of the earth (4.6 By BC) (30%)

2. heat generated by the decay of the long-lived radioactive isotopes of uranium (U238, U235), thorium (Th232) and potassium (K40) (70%).

Slide 8

1 Origins of geothermal energy Temperature distribution in the earth

Temperatures in the earth Geothermal gradient in the upper 150km

dT/dz ~ 30 oC/km

Slide 9

1 Origins of geothermal energy Mechanisms of heat transport in the earth

1) Heat transport by conduction

Fourier’s law

Thermal conductivity of rocks

Slide 10

1 Origins of geothermal energy Mechanisms of heat transport in the earth

(2) Heat transport by

convection

Mantle convection driving

the plates

Numerical simulation of

Mantle convection

Slide 11

1 Origins of geothermal energy Heat flow at the earth’s surface

Average heat flow

= 60mW/m2

Compare with

Solar Constant

S= 1360 W/m2

Note the large lateral variations across the surface of the earth

Explanation by

Theory of

Plate Tectonics

Slide 12

1 Origins of geothermal energy The earth’s thermal regime and relation with plate tectonics

Slide 13

1 Origins of geothermal energy The earth’s thermal regime and relation with plate tectonics

Plates, plate boundaries and distribution of volcanoes across the earth

Slide 14

1 Origins of geothermal energy Plate tectonics and geothermal fields

World pattern of plates, oceanic ridges, oceanic trenches, subduction zones, and geothermal fields.

http://www.geothermal-energy.org/105,interactive_map.html

Slide 15

Classification of geothermal systems/reservoirs

The “ideal geothermal reservoir”

= high temperatures + water

= steam!!!

Slide 16

2. Classification of geothermal systems/reservoirs

Thermal processes in an “ideal geothermal reservoir” resulting in the

formation of hot steam

Slide 17