Sunday, November 30, 2014

Geophysical Methods for Geothermal Exploration


Gravimetry studies changes in density to characterize subsurface properties. This method is well applied when identifying dense subsurface anomalies including granite bodies , which are vital to locate in the geothermal exploration projects. Subsurface fault lines are also identifiable with gravitational methods. These faults are often identified as prime drilling locations as their densities are much less than surrounding materials.
Changes in groundwater levels may also be measured and identified with gravitational methods. This recharge element is imperative in creating productive geothermal systems. Pore density and subsequent overall density are affected by fluid flow and therefore change the gravitatonal field.


Magnetotellurics (MT) measurements allow detection of resistivity anomalies associated with productive geothermal structures.
Geological materials are generally poor electrical conductors and have a high resistivity. Hydrothermal fluids in the pores and fractures of the earth , however, increase the conductivity of the subsurface materials. This change in conductivity is used to map the subsurface geology and estimate the subsurface material composition. Resistivity measurments are made using a series of probes distributed tens to hundreds of meters apart, to detect the electrical response of the earth.
Since flowing geothermal waters can be detected as zones of low resistance, it is possible to map geothermal resources using such a technique.

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