Numerical simulation of convective closed-loop geothermal heat extraction from an idle geothermal well in eastern Indonesia

Abstract

A geothermal resource typically experiences a production decline caused by exploitation activities. Once the power generation from the resource reaches its subeconomic threshold, the production activities might be abandoned, and the production wells are converted into idle wells. However, idle geothermal wells still have thermal energy from the geofluid inside the wellbore that could be extracted to extend the economic lifetime of the well. In this study, a convective closed-loop geothermal (CLG) heat extraction system from an idle geothermal well is developed. It is performed through numerical simulation using COMSOL to calculate and optimize the rate of heat extraction. Convective CLG systems offer the advantage of having higher heat transfer rates than conductive CLG systems in hot dry rocks. In the numerical model, a hypothetical idle geothermal well is created based on the typical conditions of geothermal fields in eastern Indonesia with a depth of 500 m and a bottom hole temperature of 190oC. A closed-loop coaxial borehole heat exchanger (BHE) is inserted into the wellbore to extract the geofluid’s heat by injecting water as the working fluid into the BHE’s annulus. The numerical model results suggest that the optimized BHE could extract up to 185.48 kW of thermal energy.