Geothermal energy from abandoned oil and gas wells using water in combination with a closed wellbore

Abstract Binary cycle power plants have been used successfully for electricity generation utilizing co-produced fluids from active onshore oil wells. Adapting this process for use on abandoned wells by circulating the binary working fluid down the wellbore has been previously proposed and a selection of fluids evaluated. This work proposes and evaluates an approach using water as the wellbore fluid in combination with abandoned wells and a closed wellbore. The wellbore is therefore used as a heat exchanger. The aim is to enable electricity generation via a binary cycle plant while mitigating contamination risks associated with the circulation of conventional organic working fluids. Well log data for over 2500 wells in Texas are used to assess the use of wellbores in this way and for calculation of geothermal gradient and surface temperature. Wellbore heat transfer and wellbore thermal resistance are calculated. With a geothermal gradient of 0.0311 °C/m, a fluid temperature of 130 °C is achieved using a wellbore depth of 4200 m and a mass flow rate of 2.5 kg/s. Flow rates up to 15 kg/s are shown using greater wellbore depth. Head loss and pumping requirements are calculated relative to wellbore depth with results finding maximum head loss and corresponding pump requirements remain small for the mass flow rates evaluated. Net power figures of 109 kW-630 kW are obtained utilizing a binary cycle power plant with a multistage heat exchanger. The use of abandoned wells as a means of generating electricity with water as the wellbore circulating fluid, utilising a method with no reliance on naturally occurring geothermal fluid is shown, offering a potential use for a global resource that is as yet unused.