Time Zero for Net Zero: A Coal Mine Baseline for Decarbonising Heat

Abstract

Mine water geothermal energy could provide sustainable heating, cooling and storage to assist in the decarbonisation of heat and achieving Net Zero carbon emissions. However, mined environments are highly complex and we currently lack the understanding to confidently enable a widespread, cost-effective deployment of the technology. Extensive and repeated use of the mined subsurface as a thermal source/store and the optimisation of operational infrastructure encompasses a range of scientific and technical challenges that require broad partnerships to address. We present emerging results of a pioneering multidisciplinary collaboration formed around an at-scale mine water geothermal research infrastructure in Glasgow, United Kingdom. Focused on a mined, urban environment, a range of approaches have been applied to both characterise the environmental change before geothermal activities to generate “time zero” datasets, and to develop novel monitoring tools for cost-effective and environmentally-sound geothermal operations. Time zero soil chemistry, ground gas, surface water and groundwater characterisation, together with ground motion and seismic monitoring, document ongoing seasonal and temporal variability that can be considered typical of a post-industrial, urban environment underlain by abandoned, flooded coal mine workings. In addition, over 550 water, rock and gas samples collected during borehole drilling and testing underwent diverse geochemical, isotopic and microbiological analysis. Initial results indicate a connected subsurface with modern groundwater, and resolve distinctive chemical, organic carbon and stable isotope signatures from different horizons that offer promise as a basis for monitoring methods. Biogeochemical interactions of sulphur, carbon and iron, plus indications of microbially-mediated mineral oxidation/reduction reactions require further investigation for long term operation. Integration of the wide array of time zero observations and understanding of coupled subsurface processes has significant potential to inform development of efficient and resilient geothermal infrastructure and to inform the design of fit-for-purpose monitoring approaches in the quest towards meeting Net Zero targets.

Moving From “Doing to” to “Doing With”: Community Participation in Geoenergy Solutions for Net Zero—The Case of Minewater Geothermal

“…Many of the towns and cities in the UK and across Europe are areas of former coal mining activity and the shallow flooded mine workings are prospective to heat local homes and businesses (Walls et al, 2021). Projects worldwide have demonstrated mine water heating, cooling and inter-seasonal storage (Walls et al, 2021) and widespread scale up is anticipated (Watson et al, 2019;Monaghan et al, 2022).…”

“…• While MWGE is an emerging technology, global resource estimates are large (Monaghan et al, 2022). There is particular interest in minewater geothermal in the UK and Europe as a pathway to accelerate heat decarbonisation: there is significant potential for MWGE projects to provide low carbon heat to homes and businesses local to the resource (Watson et al, 2019;Abesser and Walker, 2022).…”

Heat Recovery Potential and Hydrochemistry of Mine Water Discharges From Scotland’s Coalfields

“…The use of open loop abstraction-reinjection (well doublet) heat exchange systems based on shallow groundwater is globally widespread (Jessop et al, 1995;Verhoeven et al, 2014;Ramos et al, 2015;Walls et al, 2021;Monaghan et al, 2022a;Banks et al, 2022), and is similar to configurations found in other geothermal reservoir types such as hot dry rock and hot sedimentary aquifers (Limberger et al, 2018;Reinecker et al, 2021). However, there are alternative configurations by which mine water's thermal energy can be harnessed (Banks et al, 2019;Walls et al, 2021), each accompanied by varying drilling costs and project risks (Monaghan et al, 2022b).…”

“…However, there are alternative configurations by which mine water's thermal energy can be harnessed (Banks et al, 2019;Walls et al, 2021), each accompanied by varying drilling costs and project risks (Monaghan et al, 2022b). Detailed understanding of mine water geothermal energy resource size and sustainability remains largely in its research phase, with increasing numbers of projects being started (Walls et al, 2021;Monaghan et al, 2022a;Banks et al, 2022). Owing to the heterogeneous nature of mine workings, each project has unique hydrogeological properties, thus uncertainty around the speed and extent of heat migration within mines and initial resource scale and availability are regarded as significant project risks during the planning stage (Walls et al, 2021).…”