Modelled hot sedimentary aquifer geothermal potential of Upper Devonian strata in the Midland Valley of Scotland

Kearsey, T.I.; Receveur, M.; Monaghan, A.A.. 2024 Modelled hot sedimentary aquifer geothermal potential of Upper Devonian strata in the Midland Valley of Scotland. Nottingham, UK, British Geological Survey, 43pp. (OR/24/030) (Unpublished)

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Abstract/Summary

A regional-scale estimate of the Heat-In-Place for the ‘hot sedimentary aquifer’ (or ‘hydrothermal’) potential geothermal energy source in the sandstone-dominated strata of central Scotland has been conducted for the first time. This report describes the lithology and rock properties of the target units now classified as Upper Devonian in age – the Kinnesswood Formation and Stratheden Group – the construction of an updated 3D geological model of depth and thickness, as well as values and assumptions used for the potential geothermal energy source estimation. The modelled distribution and estimation of the potential resource are provided with high uncertainty due to the data quantity and quality for the Kinnesswood Formation and Stratheden Group target, where buried at several kilometres depth. Uncertainties range from the presence and thickness of the units to their porosity, permeability and temperature. This estimation represents a starting point for more detailed analysis and interpretations, highlighting potential opportunities from 44-166°C at depths of up to 6 km. Ultimately, deep geothermal wells need to be drilled to de-risk the target. The resource potential for direct heat utilisation is assessed using an upper 1.4 km depth cut-off relative to Ordnance Datum, at which the average of the collected temperature data approximates to 50°C. Using the statistical approach of the heat calculator of Piris et al. (2021), the modelled results are P10 = 361.1 EJ, P50 = 341.7 EJ, P90 = 312.5 EJ for the modelled Heat-In-Place and tentatively P10 = 51.4 GW, P50 = 35.6 GW, P90 = 23.2 GW for the modelled recoverable heat. The values are decreased by approximately a third by removing areas further than 1 km offshore in the Firth of Forth, for which the heat demand and techno-economics would be significantly different. Resultant Heat-In-Place values for onshore and within 1 km of the coastline are P10 = 257.8 EJ, P50 = 243.9 EJ and P90 = 223.1 EJ, and P10 = 36.7 GW, P50 = 25.4 GW and P90 = 16.6 GW for modelled recoverable heat. After establishing the presence and thickness of the target geothermal reservoir, the achievable and sustainable flow rate is a key parameter for a potential hot sedimentary aquifer estimation. Aquifer properties of the Kinnesswood Formation and Stratheden Group target vary from 0–31.2% and 0.004–2212 mD close to surface and in the Glenrothes borehole at 428 m, through intergranular and fault/fracture flow. The variability represents different beds and spatial locations highlighting the heterogeneity of the target aquifer/reservoir. The Knox Pulpit Formation and lateral equivalents are believed to be the most homogenous. A key uncertainty to the geothermal potential across the Midland Valley of Scotland remains whether the aquifer properties deteriorate at depths greater than 500 m. Despite the high geological uncertainty, the hot sedimentary aquifer presents significant opportunity for a decentralised heat supply in central Scotland, coincident with some major population centres including Stirling, Glasgow, Falkirk and Dunfermline. Compared to other UK geothermal opportunities (e.g. Permo-Triassic sandstones: 8 EJ Worcester Basin, 122 EJ Eastern England in Abesser et al. 2023) the Heat-In-Place values are large due to the greater depth and unit thickness combined with moderate porosity values, though the geological uncertainty is higher. Sandstone-dominated units of Strathmore basin (Lower Devonian), Moray and Caithness basins (Devonian), the Borders (Upper Devonian) and Dumfries and Galloway (Permian) forming moderate, high and very high productivity aquifer units at outcrop and shallow subsurface across Scotland form potential aquifer geothermal opportunities. They have not been assessed during this study due to lack of subsurface data. The Passage Formation high productivity aquifer (Carboniferous) was included in this model and assessment but with maximum burial depths of around 1 km onshore (corresponding to maximum estimated temperatures of around 34°C), this unit will be considered further in a separate analysis of the shallower, lower temperature geothermal energy source for open loop ground source heat systems, along with the shallower parts of the Upper Devonian strata modelled here.

Item Type:	Publication - Report
Funders/Sponsors:	British Geological Survey
Additional Information. Not used in RCUK Gateway to Research.:	This item has been internally reviewed, but not externally peer-reviewed.
NORA Subject Terms:	Earth Sciences
Date made live:	19 Dec 2024 16:43 +0 (UTC)
URI:	https://nora.nerc.ac.uk/id/eprint/538341

Item Type:

Publication - Report

Funders/Sponsors:

British Geological Survey

Additional Information. Not used in RCUK Gateway to Research.:

This item has been internally reviewed, but not externally peer-reviewed.

NORA Subject Terms:

Earth Sciences

Date made live:

19 Dec 2024 16:43 +0 (UTC)

URI:

https://nora.nerc.ac.uk/id/eprint/538341