Resistivity Imaging as a Tool for Geothermal Exploration

 

 

 

 

 

 

 

 

 

 

Formally, resistivity is a measure of the resistance of a material to current flow, multiplied by the cross-sectional area of the current path, divided by the path length. Mathematically, resistivity is = R(l/A) where R is the resistance of the medium, l is the current path length, and A is the cross-sectional area. Thus, has dimensions of m.

Resistivity is widely used in geophysical exploration. Its applications include, but are not limited to: subsurface geological investigation, cavity detection, water table delineation, leakage investigation of dam sites, and geothermal exploration. As the name implies, resistivity imaging displays spatial distributions of resistive anomalies. Cavities and geothermal regions appear as red areas, indicating that they are very resistive relative to their surroundings, and water tables and dam seepage appear as blue areas, indicating conductive regions.

The figure above is a resistivity image of a known geothermal reservoir in Sulphur Springs, St. Lucia, West Indies. Lines 1-7 and SL1 and SL2 indicate exploratory boreholes that have been drilled over the past several decades. It is from these boreholes that we gather a rough idea of the geothermal field (the dashed lines) and the resistivity image clearly captures these features.

Notably, a British team originally collected the resistivity data in the 1970s and the Earth Resources Laboratory (Department of Earth, Atmospheric, and Planetary Sciences, M.I.T.) inverted these data using a proprietary 2-dimensional inversion algorithm. The inversion returns a spatially accurate depiction of the true resistivity at depth—a result that was difficult or impossible to attain in the 70s.

Return to Environmental Research