Oilfield geothermal resources of the Upper Assam Petroliferous Basin, NE India

Abstract

Extracting geothermal energy from the oil-producing fields is an experimental venture globally. The exploitation and utilization of geothermal energy can partly reduce the larger dependence on conventional non-renewable energy sources like oil, gas, coal, and other fossil fuels, and has a bright prospect. The Upper Assam Basin is a mature petroliferous basin of NE India, where there are several hundred low production, high water cut, or abandoned oil and gas wells that can be retrofitted as geothermal wells instead of drilling new ones. This will help bridge the gap of growing energy demand and limited supply in energy-deficient state like Assam. Situated away from the active plate boundaries and in lack of active volcanism, the Upper Assam Basin remains a low-to-medium enthalpy geothermal fluid regime. The deeper reservoir in this regard can, therefore, be the best candidate for the introspection of the potential geothermal energy reservoir reconnaissance. The selection of a deeper horizon considered in the present case has been the stratified reservoirs of the Lakadong-Therria (Lk-Th) Formation, Sylhet Group of the Lower Eocene age occurring at a variable depth of 3400 m–4600 m. The Lk-Th Formation possesses a fair-quality reservoir with lateral continuity and favourable petrophysical properties. In this study, representative gamma-ray (GR) and resistivity (R) logs were examined to work out lithology, and bed boundary demarcation, etc. The total Formation thickness varies from 97 to 157 m; the individual sand body thickness is up to 6 m. Other reservoir parameters, e.g., porosity (Φ = 8–33 %), water saturation (Sw = 4.57–95.15 %), geothermal gradient (2.71 °C/100m to 3.92 °C/100 m at 4300 m and 3608 m) respectively, and theoretical estimate of high heat flux in the range 70–100 mW/m2/s, are the necessary yard-stick to measure the subsurface geothermal reserves. Efficient energy extraction will have the potential in facilitating energy utilization for industrial purposes, especially in tea processing units present nearby oilfields and also for power generation by the binary mechanism.