The need to regulate thermal interference between mine water geothermal systems: a UK perspective

Mine water geothermal (MWG) technology can provide substantial amounts of decarbonized heat and is gaining traction in the UK with several active projects. However, the lack of regulations concerning potential subsurface thermal interference is hindering wider adoption. Using the GEMSToolbox modelling tool, we examined a generic room and pillar coal mine to assess the impact of thermal interference between adjacent MWG systems. The modelling quantifies the thermal interference occurring between two operators sharing a contiguous water body within a mine block. High water abstraction rates and smaller distances between the MWG wells increase the risk of significant interference, which worsens the longer the systems operate. We introduce the ‘heat extraction ratio’ to quantify thermal interference, defined as the ratio of heat produced with two users present compared with a single user. This metric can aid regulators in establishing acceptable levels of thermal interference between MWG systems. Drawing on regulations from geothermal energy-producing countries, ground source heat pump guidelines and UK oil and gas laws, we propose two potential policies for managing MWG thermal interference. The first policy requires unitization when thermal interference exceeds a certain threshold, and the second policy disallows additional systems if they would breach the regulatory threshold.