Geothermal potential of Manuguru geothermal field of Godavari valley, India

Abstract

The Godavari geothermal field in India is one of the potential areas manifested by several geothermal waters and groundwaters. The geothermal waters of the area are near neutral (pH: 6.5–7.3) with surface temperature ranging from 30 to 55 °C while groundwaters are also near neutral (pH: 6.6–7.5) with surface temperature ranging from 24 to 28 °C. The hydrogeochemistry of the geothermal waters suggests that the geothermal waters show a Na-Ca-SO4-HCO3 to a Ca-HCO3 type and groundwaters are of the Ca-HCO3 to Na-Ca-HCO3 type while groundwaters and river waters are of the Ca-Na-SO4 types. The geothermal waters of the study area are enriched in SO42– and Cl–, due to the interaction with the pyrite-bearing Gondwana sediments and granitic gneiss basement rocks. Furthermore, enrichment of Ca2+, Mg2+ and an increased HCO3/Cl ratio in geothermal water is caused by the exchange and/or mixing process that takes place during water-rock interaction at an elevated temperature while ascending to the surface. This type of behavior of water is also observed during the water-rock interaction experiment at 100 °C. Studies on geothermal gas geochemistry suggest the deeper circulation of geothermal waters in the crust and high helium concentration as a thermal gas that can be utilized for commercial purposes. Estimated reservoir temperatures from quartz and Na-K-Ca geothermometry are in the range 110–195 °C. Therefore, the geothermal water of the study area is categorized as a moderate enthalpy geothermal system. Thermal logging in the borewell and depth range from 50 to 1000 m suggest that the geothermal gradient in the Manuguru area ranges from 22.5 to 105.5 °C/km and heat flow ranges from 83 to 388 mW/m2, which is higher than the regional condition. Therefore, 3584 MWe power can be produced by using the Organic Rankine Cycle (ORC) from the Manuguru geothermal area of Godavari valley