Putting the Potential of Deep Borehole Heat Exchangers Into Perspective: a Gas Well Repurposing Case Study, Onshore in the UK

Abstract

Unlike open-loop geothermal systems, closed-loop types require no direct hydraulic interactions with a reservoir. Deep Borehole Heat Exchangers (DBHEs) consist of a single closed well configuration, with conductive heat transfer taking place between a circulating fluid and the surrounding geological formations through the borehole walls. There is potential to offset drilling costs of DBHEs by repurposing abandoned or suspended oil and gas wells or unsuccessful geothermal exploration wells. However, due to the much smaller volume of subsurface rock that can contribute to heat transfer, in addition to exergy losses and low conversion efficiencies, DBHEs have limited potential for electricity generation. Nevertheless, they can contribute to the decarbonization of heating and cooling as proven by the number of DBHE projects already implemented in China. This paper is based on a demonstration project, located in northern England, which aims to assess the feasibility of repurposing a deep, tight gas appraisal well as a DBHE. The results of independent modeling work are presented which extend the wellbore performance to include connectivity to different surface uses of thermal energy. The findings highlight that different modi operandi of a given DBHE correspond to different levels of success, and expectations need to be commensurate to the intended end-use.