| Abstract: | The electrical resistivity technique has been used extensively in the Indian sub-continent for the exploration of geothermal areas. The first systematic application of the resistivity method for locating the geothermal reservoir was made in the Puga area, which is situated very close to the collision junction of the Indian and the Asian plates and has numerous hot springs with temperatures varying from 30 to 84°C (boiling point at that altitude). The resistivity depth probes indicated the presence of a conductive zone, with a value of 10–25 ohm·m and a thickness varying from 50 to 300 m over an area of 3 km2, which was inferred to correspond to a shallow thermal reservoir. Thermal surveys also revealed a significant anomaly corresponding to this zone, which, when drilled, encountered a reservoir of wet steam with a temperature of up to 135°C, thus confirming the results of the resistivity surveys. Somewhat similar results have been obtained in the adjoining area, where much thicker zones with moderate electrical conductivity have been mapped.Another significant application of the electrical resistivity method has been made in the NNW-SSE extending West Coast geothermal belt of India, which is covered by Traps (Basalts) of the Cretaceous-Eocene. The area is characterized by the existence of a number of hot springs, with temperature up to 70°C, along a 400 km long alignment, associated with steep gravity gradients and an isolated occurrence of native mercury in the zone of a gravity “high”. The enigmatic geology of this area has been mapped, giving quantitative estimates of the thickness of the Traps and inferring the structural features. In addition, the electrical resistivity depth probes have also been used to identify the pre-Trappean geology, thereby locating the probable areas which could act as geothermal reservoirs.This paper presents the results of the electrical resistivity surveys in the form of geoelectric sections for some of the geothemal fields in the Indian sub-continent. |
