Borehole temperature log from the Glasgow Geothermal Energy Research Field Site: a record of past changes to ground surface temperature caused by urban development

Abstract

As part of the Glasgow Geothermal Energy Research Field Site (GGERFS) project, intended as a test site for mine-water geothermal heat, the GGC-01 borehole was drilled in the Dalmarnock area in the east of the city of Glasgow, starting in November 2018. It was logged in January 2019 to provide a record of subsurface temperature to 197 m depth, in this urban area with a long history of coal mining and industrial development. This borehole temperature record is significantly perturbed away from its natural state, in part because of the ‘permeabilizing’ effect of past nearby coal mining and in part due to surface warming as a result of the combination of anthropogenic climate change and creation of a subsurface urban heat island by local urban development. Our numerical modelling indicates the total surface warming effect as 2.7°C, partitioned as 2.0°C of global warming since the Industrial Revolution and 0.7°C of local UHI development. We cannot resolve the precise combination of local factors that influence the surface warming because uncertainty in the subsurface thermal properties trades against uncertainty in the history of surface warming. However, the background upward heat flow through the shallow subsurface is estimated as only c. 28–33 mW m−2, depending on choice of other model parameters, well below the c. 80 mW m−2 expected in the Glasgow area. We infer that the ‘missing’ geothermal heat flux is entrained by horizontal flow at depth beyond the reach of the shallow GGC-01 borehole. Although the shallow subsurface in the study area is warmer than it would have been before the Industrial Revolution, at greater depths – between c. 90 and >300 m – it is colder, due to the effect of reduced background heat flow. In future the GGERFS project might utilize water from depths of c. 90 m, but the temperature of the groundwater at these depths is maintained largely by the past effect of surface warming, due to climate change and urban development; it is thus a resource that might be ‘mined’ but not sustainably replenished and, being the result of surface warming rather than upward heat flow, arguably should not count as ‘geothermal’ heat in the first place. Our analysis thus indicates that the GGERFS site is a poor choice as a test site for mine-water geothermal heat.Supplementary material: A summary history of coal mining in the study area is available at: https://doi.org/10.6084/m9.figshare.c.4911495.v2

Repurposing Hydrocarbon Wells for Geothermal Use in the UK: The Onshore Fields with the Greatest Potential

“…The potential value of both these heat sources was discussed by [77]. Next are the hypothetical minewater geothermal scheme at Polkemmet in central Scotland and the Glasgow Geothermal Energy Research Field Site (GGERFS), both as discussed by [78]. Nominal calculations have been provided for the Stockbridge and Welton oilfields, in addition to the analyses of the Wytch Farm and Wareham fields.…”

“…Next are minewater geothermal schemes, at Heerlen, Dannenbaum, Springhill, and Dawdon, the heat production well at Southampton in southern England, and example projects in the Paris Basin of central France (Issy-les-Moulineaux) and the Aquitaine Basin of SW France (Jonzac). [78] Sites in each group are listed in order of thermal power output, Q. T O is the source temperature of the produced water; except where otherwise indicated, T S is the annual mean air temperature at the sites, obtained from meteorological data. Countries where projects are located are denoted thus: CA, Canada; D, Germany; F, France; ES, Spain; NL, the Netherlands; and UK, the United Kingdom.…”

“…Finally, two projects, the operational Dawdon minewater heat project and the GGERFS, stand out on account of their low (actual, or potential) thermal power outputs. The GGERFS is a test site for minewater geothermal heat production [94,95] and is not currently used for heat production or storage (hence its inclusion here as a 'potential' site), but has been strongly criticized [78] as some of its design features impose severe constraints on the potential heat output. Notable features are its shallow depth, <100 m, and resulting very low reservoir temperature, and its close spacing of candidate injection and production wells, <100 m to several hundred metres (e.g., [96,97]), which compare with horizontal scales of many hundreds of metres to kilometres and depths of hundreds of metres at other modern minewater geothermal projects such as Heerlen [82] and Dannenbaum [88].…”

“…Notable features are its shallow depth, <100 m, and resulting very low reservoir temperature, and its close spacing of candidate injection and production wells, <100 m to several hundred metres (e.g., [96,97]), which compare with horizontal scales of many hundreds of metres to kilometres and depths of hundreds of metres at other modern minewater geothermal projects such as Heerlen [82] and Dannenbaum [88]. From the point of view of achieving significant decarbonisation, the recent emphasis in the UK on these very small-scale projects [93][94][95] (and, in the case of the GGERFS, commitment of significant funding, the budget being £9 million [78]) seems unfortunate, when other much more promising geothermal heat sources are readily available. Comparison of thermal output power, P, versus output temperature for the suite of lowtemperature geothermal sites listed in Table 8.…”

Discussion on ‘Borehole temperature log from the Glasgow Geothermal Energy Research Field Site: a record of past changes to ground surface temperature caused by urban development’, Scottish Journal of Geology , 56, 134-152, https://doi.org/10.1144/sjg2019-033

“…In their analysis of temperature data, Watson and Westaway (2020) make substantial use of initial open information provided by the UK Geoenergy Observatory: Glasgow Geothermal Energy Research Field Site. They also offer criticisms on site location, heat resource size, design and costs; however, these criticisms appear to be based on a misunderstanding of the purpose of the Glasgow Observatory.…”