Borehole Temperature Research Articles

Shallow hot-point drill system for active layer temperature measurement along Zhongshan–Dome A traverse, Antarctica

AbstractIn glaciology, snow–firn temperature at 10 m is considered a representation of the mean annual air temperature at the surface (MAAT) of the studied site. Although MAAT is an important parameter in ice-sheet investigations, it has not been widely measured in Antarctica. To measure the 10 m snow–firn temperature in Antarctica, a shallow hot-point drill system is designed. In this simple and lightweight system, a hot-point drill can melt boreholes with a diameter of 34 mm in the snow–firn to a depth of 30 m and a temperature sensors string can measure the borehole temperature precisely. In the 2018/19 field season, 16 boreholes along the Zhongshan–Dome A traverse were drilled, and the borehole temperature was measured. Although certain problems existed pertaining to the hot-point drill, a total depth of ~244 m was successfully drilled at an average penetration rate of ~10 m h−1. After borehole drilling, ~12–15 h were generally required for the borehole to achieve thermal equilibrium with the surroundings. Preliminary results demonstrated that the 10 m snow–firn temperature along the traverse route was affected by the increasing altitude and latitude, and it decreased gradually with an increase in the distance from Zhongshan station.

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. In order to mitigate misapprehensions for future Observatory users, we write in reply. The Glasgow Observatory has been developed as a multidisciplinary research facility; it is not a demonstrator of maximum mine water heat resource, which is by implication what Watson and Westaway (2020) would deem a success.

Twentieth century warming reflected by the Malan Glacier borehole temperatures, northern Tibetan Plateau

ABSTRACT The Tibetan Plateau is a high-elevation area in Asia and contains the largest volumes of glaciers outside the polar regions. Reconstruction of the glacier surface temperature history in this area is crucial for better understanding of the process of climate change in the Tibetan Plateau. The Tikhonov regularization method has been used on borehole temperatures measured at Malan Glacier, located on the north Tibetan Plateau, to reconstruct the surface temperature history in the twentieth century. We found that the glacier surface temperature, which rose significantly after the 1960s, increased about 1.1°C over the last century. The warmest period occurred in the 1980s to the 1990s and the highest temperature variation could be 1.5°C to 1.6°C. The results were also compared with those of nearby instrumental temperatures by Wudaoliang meteorological station and the stable oxygen isotope () from the Malan ice core.

Ground thermal regimes and implications for permafrost distribution on Kilimanjaro, Tanzania

ABSTRACT Tropical mountain permafrost has a unique thermal regime due to ground surface exposure to strong solar radiation. The intensity of the surface offset resulting from snow cover also strongly affects the absence or presence of permafrost. Latent heat transfer and reflected solar radiation (higher albedo) that occur during the snow-covered season contribute to a positive feedback that cools the ground. Eleven ground temperature monitoring sites were established on the mountain at 2,780 to 5,820 m.a.s.l. The geothermal heat flow is locally high in the caldera of this volcano, as shown by borehole temperature data. Permafrost is located near the only glacier entirely within the caldera (Furtwängler). These three-year continuous records of ground temperature data encompass years of high and low snow cover. Our results show that the current lower boundary of permafrost is slightly above summit altitude and relict permafrost is present due to the influence of saturated sand on latent heat transfer. Permafrost tends to be lost more rapidly during drought years. The remaining permafrost seems likely to disappear in the future. The presence of permafrost and its thermal resistance depends on the ice content of caldera sand and the duration of snow cover.

DEFINING GEOEXCHANGE EXTRACTION RATES IN THE SAME GEOLOGICAL ENVIRONMENT FOR DIFFERENT BOREHOLE GEOMETRY SETTINGS – PILOT RESULTS FROM THE HAPPEN - HORIZON 2020 PROJECT

Kindergarten Grdelin in the city of Buzet, Istria, Croatia, was chosen to undergo a deep retrofit of the current thermotechnical system, as a part of the HORIZON 2020 HAPPEN project1. The existing shallow spiral heat exchanger field is insufficient to cover heating loads of the building. Therefore, additional BHEs were drilled and completed to determine optimal borehole heat exchanger type within the same geological environment. Four BHEs, either single U (1U) or double U (2U), with different geometrical setting and depth were tested: BHE-1 (50 m, 2U DN32 ribbed), BHE-2 (75 m, 2U DN40 ribbed), BHE-3 (100 m, 2U DN32 smooth) and BHE-4 (150 m, 1U DN45 ribbed). A thermal response test (TRT) was performed to obtain the ground thermal properties. Furthermore, synthetic TRT curves were calculated to describe temperature response in the case of different heat pulses. This was done to determine heat extraction rates and the capacity of each BHE type, according to EN14511 norm. It was established that the BHE-4 is the optimal design for heating and cooling purposes on the selected site due to positive impact of the geothermal gradient, higher initial borehole temperature and a positive effect of the ribbed inner wall.

A Comparison of Frequency Domain Electro-Magnetometry, Electrical Resistivity Tomography and Borehole Temperatures to Assess the Presence of Ice in a Rock Glacier

Alpine permafrost is currently warming, leading to changes such as active layer deepening and talik formation. Frequency domain electro-magnetometry (FDEM) measurements were tested as a simple and efficient method to investigate ground characteristics along two transects on the ice-rich Schafberg rock glacier in the Eastern Swiss Alps. The results were compared with electrical resistivity tomography (ERT) and ground temperature data acquired simultaneously in boreholes. FDEM provides information on the electrical properties of the ground, allowing to investigate ground-ice distribution. Our device allowed measurements to a depth of around 7 m. In ice-rich permafrost, FDEM can provide an approximation of the active layer thickness, and ice-free zones within the permafrost such as intra-permafrost taliks can be identified. This rapidly applicable geophysical method can be used to monitor ground ice distribution easily and efficiently, making it an ideal complement to borehole temperature data, which only provide point information and are costly to install and maintain. At the Schafberg site the three methods FDEM, electrical resistivity tomography and borehole temperature measurements provided similar results, with regard to active layer thickness and the presence of unfrozen zones within the ice-rich permafrost.

Research and application of the underground fire detection technology based on multi-dimensional data fusion

Underground mining has been plagued by gob fires triggered via self-igniting coal, the emission of toxic fumes, particulate matter, and possibly induced explosions from the gob fires make mining extremely dangerous. The spontaneous combustion of underground coal seriously affects the mining of adjacent coal seams and the overall safety production. The key to control the shallow coal seam fire is to accurately locate its the location and scope by surface detection method. Based on the non-dimensional normalization processing of different types of data and the weight analysis of analytic hierarchy process (AHP), a multi index data fusion method of temperature, gas and radon concentration was proposed by using the practical radon measurement, borehole temperature measurement and gas measurement methods, and the index of fire zone delineation (IFZD) based on multi-dimensional data fusion was obtained. According to the content total method based on fractal theory, the anomalousthreshold of IFZD was determined by piecewise linear fitting in double logarithmic coordinates. Eventually, the multi-dimensional data fusion underground fire detection method was established completely, and the method was applied to the fire detection of shallow coal seam in typical integrated mine. The results showed that the weight coefficients of the detection indexes (CO, CO2, SO2, temperature and radon) in the fire area were 0.12, 0.03, 0.05, 0.12, 0.68, and the lower bound of the anomaly of IFZD was 0.29. According to the comprehensive isoline map, abnormal area plan and stereogram drawn through IFZD and its outlier threshold, there were eight areas with the total area of 27061 m2, which developed from the abandoned well, main well location to the southwest and northeast. The isolines of abandoned air shaft and main shaft were densest and the value was the largest, indicating that coal oxidation in this area is severest, so it is necessary to strengthen the ground fracture investigation and sealing. This method solved the problems such as poor accuracy of single index circle fire zones, and difficulty in direct fusion of multi-index data with different dimension and range, and difficulty in determining the abnormal lower boundary of the fusion index after dimensionless normalization, which provided a new technical method support for the detection of underground shallow coal seam fire area.

Deep geothermal energy in northern England: Insights from 3D finite difference temperature modelling

Many of the most widely used deep geothermal resource maps for the UK are produced by contouring around sparsely distributed and often unreliable data points. We thus present a MATLAB-based 3D finite difference temperature modelling methodology, which provides a means for producing more resolute and geologically realistic versions of these maps. Our case study area in northern England represents an area where both sedimentary basins and radiothermal granite bodies comprise potential geothermal resources. We divide our 3D model into geological units, which are then assigned separate thermal properties. Assuming conductive heat transfer and steady-state and fixed boundary conditions, we calculate 3D regional subsurface temperature. Due to our averaging technique for thermal properties, the resolution of our geological model is scarcely compromised with respect to similar finite element methods. One predicted ‘hot spot’ at 1 km depth in the central part of our case study area corresponds with the granitic North Pennine Batholith. Other shallow hot spots correspond with thermally insulating sedimentary rock units and geological structures that incorporate these units. Predictive heat flow density maps highlight areas with accelerated surface heat flow associated with shallow conductive basement rock and heat producing granite bodies. Our predicted subsurface temperatures show broad similarities with measured equilibrium borehole temperatures. Inaccuracies may relate to convective heat transfer involving fault systems, or input variables relating to the geological model. Our predictive subsurface temperature and heat flow density maps are more resolute and geologically realistic relative to pre-existing contoured maps. The method presented here represents a useful tool for understanding controls on subsurface temperature distribution and geothermal potential.

Fluid flow and fault-related subsurface fractures in slate and metasandstone formations: A case study of the Jentse Geothermal Area, Taiwan

Permeable structures associated with faults are commonly treated as geothermal fluid conduits in most tight geothermal reservoirs. However, the properties of permeable structures within fault zones remain unclear due to the lack of subsurface geological data, e.g., the geothermal systems in the tight slate and metasandstone formations in Northeastern Taiwan. This study presented standard open-hole and Fullbore Formation MicroImager (FMI) logs acquired in the 8.5-inch-diameter section of the JT-3 well (800–1475 m measured depth) in the Jentse geothermal area, Taiwan, to identify the subsurface fracture structures and the possible pathway of fluid flow. Using open-hole log data, we generate a lithology interpretation for the borehole and model the associated effective porosity. Based on the FMI images, four types of natural open fractures, two types of natural sealed fractures, and drilling-induced tensile fractures were identified. Integration of the lithological model, the effective porosity, and the types of fractures reveals one major permeable fault system comprising three permeable fault zones. The fault system is composed of both permeable fault cores marked by porous fault breccia and damage zones characterized by a large number of open-fracture planes. The static borehole temperature log also shows deflections in these interpreted permeable fractures zone. Deflections in these fracture zones that, based on petrophysical and borehole image logs, are interpreted as permeable. According to the orientations of the bed boundaries and fault planes obtained from FMI images, the fault system may have an orientation of N50–70 °E and dips 70–90˚ to the NW with a width of around 116 m. This study illustrates how subsurface structures control geothermal conduits. The concept and workflow of this study may be useful for other fault-controlled geothermal areas in Taiwan.

In-situ stress measurement technology and field application based on micro-optical imaging measurement method

In-situ stress is natural stress existing in rock masses. As an important basic parameter, accurate in-situ stress is highly beneficial to the theoretical research and engineering application of rock mechanics. In-situ tests in boreholes are the most direct and effective way to obtain in-situ stress. However, the high temperature and high water pressure testing environment in boreholes limits the application scope of measurement sensors. In this study, a micro-optical imaging measurement method is proposed. On the basis of this method, an aperture measurement device is developed, and a complete set of in-situ stress measurement technology is formed. Laboratory and field application tests are carried out. The results of the temperature and pressure test in a laboratory show that the in-situ stress test technology improves service temperature and pressure and offers an extensive application range. The field test on a shallow borehole in an iron mine roadway and a deep borehole in a shale gas exploration well reveals the deformation of the test boreholes in the process of stress relief. This result proves the feasibility of the in-situ stress measurement technology. On the basis of the theory of elasticity, in-situ stress is calculated with reference to the in-situ diameter deformation of the boreholes and the mechanical parameters of the rock core. A number of in-situ stress tests are carried out under different borehole depths, and the testing times are recorded. Results show that the application of wireline coring drilling technology speeds up the test process. Hence, it can boost the operability of the in-situ stress test. In sum, the in-situ stress measurement technology based on the micro-optical imaging measurement method is feasible and operable and may thus improve the application depth of the in-situ stress measurement method based on the stress relief method.

MAGCPD: a MATLAB-based GUI to calculate the Curie point-depth involving the spectral analysis of aeromagnetic data

The Curie point-depth, frequently related to the depth to the bottom of the magnetic source, is widely employed as an estimator of temperature at depth when borehole temperature data are not available. The Curie point-depth is calculated using the spectral analysis of the magnetic data derived from aeromagnetic or satellite surveys. In this paper, MATLAB user-friendly GUI are constructed to calculate the Curie Point Depth using the inversion of aeromagnetic data assuming 2D fractal magnetization and modeling the temperature at depth assuming a 1D steady-state conductive heat transfer model. The program, tested in synthetic and aeromagnetic data, is running under MATLAB 2020a or standalone application with these input parameters: Aeromagnetic data, fractal parameter, Curie temperature, surface temperature, thermal conductivity, surface radiogenic heat production and scaling length of surface radiogenic heat production. The radially averaged amplitude spectrum, scaled spectrum, modeled spectrum, Curie point-depth, and temperature profile at depth are the output parameters of the program. Finally, the program is tested with Texas aeromagnetic data, and the results of the Curie point-depth were compared with borehole data.

Air Convection in the Active Layer of Rock Glaciers

Coarse blocks are an abundant surface cover in mountainous permafrost landscapes. In this coarse blocky layer, air convection occurs and has a significant influence on the ground thermal regime of the underlying permafrost. Besides heat transfer through conduction, free convection of air takes place seasonally and leads to a pronounced ground cooling. Air convection has been observed and described in many field studies but is often neglected or parametrized in permafrost modeling. In the present study, air convection in the active layer of rock glaciers is explicitly modeled through a heat conduction equation coupled with Darcy’s law over a two-dimensional geometry. With a series of numerical experiments, we show its effects on the thermal regime of the underlying permafrost. The ground permeability and the thermal gradient in the active layer are the most important parameters for air convection in the ground. On field sites with a high ground permeability (order of magnitude 10 6 m2), convection plays a crucial role and is required to correctly model measured borehole temperatures. The onset of natural convection occurs at critical Rayleigh numbers and is characterized by an increase of the standard deviation of the direction and the vorticity of the airflow field in the active layer. In the numerical solutions, the internal air circulation in the coarse blocky surface layer leads to an efficient ground cooling.

Borehole temperature distribution when drilling fluid loss occurs in the two-dimensional area at the bottom-hole during drilling

During the drilling process, the temperature distributions of the borehole and the formation under the condition of drilling fluid loss have a very significant effect on the borehole pressure prediction, the rheological design of drilling fluid and the borehole stability. Aiming at the complex downhole situations as drilling fluid loss occurs during drilling, a new two-dimensional model is proposed to study the temperature distributions of the borehole and the surrounding formation in the presence of the lost circulation. The law of the borehole temperature distribution when drilling fluid loss took place in the two-dimensional area at the bottom of the well was obtained. Comparing with the scenario of no drilling fluid loss, the borehole temperature is reduced at the same well depth in the case of drilling fluid loss. The occurrence of drilling fluid loss greatly disturbs the temperature distribution of drilling fluid in the annulus in the drilling fluid loss area. The location of drilling fluid loss has a conspicuous effect on the borehole temperature distributions. The occurrence of drilling fluid loss renders a more prominent effect of casings on the temperature profile of the medium around the borehole. As the drilling fluid loss rate increases, the borehole temperature at the same well depth decreases.

Comparison of observed borehole temperatures in Antarctica with simulations using a forward model driven by climate model outputs covering the past millennium

Abstract. The reconstructed surface-temperature time series from boreholes in Antarctica have significantly contributed to our understanding of multidecadal and centennial temperature changes and thus provide a good way to evaluate the ability of climate models to reproduce low-frequency climate variability. However, up to now, there has not been any systematic model–data comparison based on temperature from boreholes at a regional or local scale in Antarctica. Here, we discuss two different ways to perform such a comparison using borehole measurements and the corresponding reconstructions of surface temperature at the West Antarctic Ice Sheet (WAIS) Divide, Larissa, Mill Island, and Styx Glacier in Antarctica. The standard approach is to compare the surface temperature simulated by the climate model at the grid cell closest to each site with the reconstructions in the time domain derived from the borehole temperature observations. Although some characteristics of the reconstructions, for instance the nonuniform smoothing, limit to some extent the model–data comparison, several robust features can be evaluated. In addition, a more direct model–data comparison based on the temperature measured in the boreholes is conducted using a forward model that simulates explicitly the subsurface temperature profiles when driven with climate model outputs. This comparison in the depth domain is not only generally consistent with observations made in the time domain but also provides information that cannot easily be inferred from the comparison in the time domain. The major results from these comparisons are used to derive metrics that can be applied for future model–data comparison. We also describe the spatial representativity of the sites chosen for the metrics. The long-term cooling trend in West Antarctica from 1000 to 1600 CE (−1.0 ∘C) is generally reproduced by the models but often with a weaker amplitude. The 19th century cooling in the Antarctic Peninsula (−0.94 ∘C) is not reproduced by any of the models, which tend to show warming instead. The trend over the last 50 years is generally well reproduced in West Antarctica and at Larissa (Antarctic Peninsula) but overestimated at other sites. The wide range of simulated trends indicates the importance of internal variability in the observed trends and shows the value of model–data comparison to investigate the response to forcings.

Assessment of climate warming in the Western Ghats of India in the past century using geothermal records

Temperature-depth profiles of boreholes of a region can be analysed to estimate the past variations in climate. Perturbations over the surface ground temperature are imparted deep into the Earth’s subsurface. Western Ghats regions of India are considered to be one of the most ecologically rich regions and also play a crucial role in deciding the climatological characteristics of the country. This study quantifies the possible climate warming or cooling in the past century in the Western Ghats using temperature-depth profiles of five boreholes in a depth range of 140–198 m located in Koyna region (17.38° N, 73.74° E) of Maharashtra state, India. The analysis shows that there has been a significant warming of 0.8 ± 0.2 °C over the past 100 years in the region. The inferred warming is comparable with the trends of meteorological records of the area which yields an increasing trend of 0.56 °C in the surface air temperature (SAT). For further validation of results, a combined study of borehole temperature profiles and surface air temperature (SAT) profiles was done which showed that the period was warmer than the earlier long-term temperature records of the region by 0.8 °C. This pre-observational mean (POM) value seems to be consistent with previously studied POMs over India. This study provides a ‘true estimate’ of climate change and can be used as a robust technique to reconstruct the past climate warming.

Research on the technology of detection and risk assessment of fire areas in gangue hills.

Coal gangue hills are prone to spontaneous combustion, thereby polluting the environment of mining areas such as the soil, groundwater, and atmosphere, and the frequent occurrence of gangue hill collapses, landslides, explosions, and other accidents can even endanger the lives and property of residents. To realize the safety management of coal gangue spontaneous combustion and evaluate its present risks, this paper selects the Dongzhou Kiln gangue hill in Zuoyun County, Datong City, China, as the research object to conduct a risk assessment study. The Dongzhou gangue hill fire area is relatively large, with a total area of 183,039m2. Smoke emission commonly occurs at the site, and the surface temperature reaches 50°C, while the CO concentration exceeds 10-3. A radon detection scheme for concealed fire zones verified with borehole temperature measurements is applied. The high-temperature area is delineated with relevant data obtained by infrared thermal imaging, radon concentration, and borehole temperature detection technologies, and a coal gangue spontaneous combustion risk assessment method is established, while the gas toxicity and explosion risks of the construction area and fire trends are analyzed. The research results indicate that there are 6 likely high-temperature regions in the test area, 4 high-toxicity areas in the drilling construction area, 1 area with a high explosion risk, and 3 areas with a high risk of spontaneous combustion. Among these areas, platform 2 is a high-risk area and needs to be carefully considered. The construction of the entire area is at high risk, including toxicity, gas explosion, and spontaneous combustion risks, and measures must be implemented to reduce the overall risk.

Stribeck performance of drilling fluids for oil and gas drilling at elevated temperatures

In oil and gas drilling, the borehole temperature can be as high as 200 °C. Using a high pressure and high temperature drilling fluid tribometer, two different lubricant additives (Additives A and B) were introduced to reduce the coefficient of friction (COF) of the drilling fluid. Stribeck curve analysis at 125 °C shows that the sliding speed does not affect the dynamic COF and the oscillatory movement yielded relatively high static COF. Oscillatory and low speed movements were employed to study temperature effects, which showed Additive A exhibiting better tribological performance (26% and 9% static and dynamic COF reductions at 150 °C). Wear mechanisms were identified by scanning electron microscopy after the tribological experiments.

Fault-Affected Fluid Circulation Revealed by Hydrochemistry and Isotopes in a Large-Scale Utilized Geothermal Reservoir

A new significant aspect in the utilization of hydrothermal energy in China is the large-scale exploitation using multiwells from a single geothermal site. This requires detailed hydrogeochemical investigations to gain insight about deep groundwater circulation. At the Xiongxian karst geothermal site in North China, where the demonstration project of large-scale utilization was conducted, 40 boreholes with depths from 1000 to 1800 m were drilled in a region of 50 km2. A total of 25 water samples were collected, and temperature loggings were conducted in 16 of these wells. At the site scale, the hydraulic head was observed to decline from SW to NE, i.e., orthogonal to that at the regional scale. Moreover, the geothermal groundwater temperature, borehole temperature gradient, and heat flow in the caprock all exhibited the same spatial trend with the groundwater head. Based on the hydrogeochemical and temperature logging data, this was explained by mixing of lateral recharging groundwater with ascending thermal fluids through the Xiongxian Fault, after excluding the causes of pumping activities and geologic structure. In addition, geothermal groundwater 81Kr age was estimated to be approximately 760 k yr, which is much older than the 14C age of 20 to 30 k yr. The older 81Kr age implies a low renewability of deep groundwater circulation, which should be considered in terms of sustainable management in relation to the large-scale utilization of geothermal resources.

Observations on the structure of Surtsey

Comparison of investigations of the 1979 and 2017 cored boreholes coupled with continued observations of the dynamic surface of Surtsey has modified our concepts of the subsurface structure of the volcano. A geometrical analysis of the 2017 vertical and inclined cores indicates that near-surface layering dips westerly, indicating that the boreholes are located inside the Surtur crater. In subaerial deposits, as well as in deep deposits below sea level and below the pre-Surtsey seafloor, there are zones of porous tuff that contain abundant pyroclasts with narrow rims of fine ash. These features, typical of near-surface deposits, could have been carried down the vent by downslumping during fluctuating explosive activity. They support the hypothesis that a broad diatreme underlies the Surtur vent. No major intrusions were encountered in the 2017 drilling except for coherent basalt in deep sub-seafloor deposits below the center of Surtur crater. The 2017 borehole temperature measurements indicate that the peak temperature in the vertical boreholes was 124 °C at 105 meters below the surface (m.b.s.) and that in the inclined hole it was 127 °C at 115 m.b.s. immediately after drilling. These peak temperatures are 72 meters apart horizontally yet closely resemble each other in shape and magnitude, suggesting a broad heat source. In addition, measurements in the inclined hole from 200 to 290 m.b.s. indicate a temperature of 60±2 °C. This is apparently residual heat from the volcanic action that created the diatreme. These facts cast doubt on the previous concept that the heat anomaly in the 1979 borehole was due to a nearby intrusion. Instead they suggest that heat would have been conducted down from the 85-meter-thick hot lava shield within the Surtur crater into a warm diatreme substrate containing original volcanic heat. As the conducted heat moved down into the water-saturated substrate it would have elevated the temperature above the boiling point curve, baked out water, and created a vapor-dominated system below sea level. Eventually loss of heat by boiling and rise of steam caused the vapor-dominated system to retreat upward. The resulting steam rose and warmed the tephra adjacent to the lava shields where it produced broad areas of palagonitized tuff.

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

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