Assessing the potential to repurpose hydrocarbon and geothermal exploration wells as closed-loop geothermal systems

There are an abundant hydrocarbon wells worldwide which are approaching their end of life, along with a small number of unsuccessful geothermal exploration wells, that have the potential to be repurposed as closed-loop geothermal systems. The most suitable method for repurposing is as a deep borehole heat exchanger, which consists of a pipe inserted down the borehole to create two coaxial concentric flow conduits – the pipe itself and the annulus between the pipe and the borehole wall. This form of technology can provide a low-risk, predictable energy supply that can meet anchor loads in heat networks and reduce the initial capital expenditure associated with drilling when using repurposed wells. However, there are weaknesses of using this technology in repurposed wells: (i) it produces significantly lower thermal power outputs than open-loop systems (wells which produce warm formation water, and which rely on advective processes); (ii) many wells that have the potential to be repurposed will be drilled in locations that are not proximal to surface heat demand; (iii) the potential for electrical power generation is usually not feasible owing to low thermal capacity and production temperatures; and (iv) there are several issues with ageing infrastructure, regulations and asset liabilities.