Digging deeper: The influence of historical mining on Glasgow's subsurface thermal state to inform geothermal research

Sean M Watson,Rob Westaway,Neil M Burnside

doi:10.1144/sjg2019-012

Abstract

Studies of the former NE England coalfield in Tyneside demonstrated that heat flow perturbations in boreholes were due to the entrainment and lateral dispersion of heat from deeper in the subsurface through flooded mine workings. This work assesses the influence of historical mining on geothermal observations across Greater Glasgow. The regional heat flow for Glasgow is 60 mW m−2 and, after correction for palaeoclimate, is estimated as c. 80 mW m−2. An example of reduced heat flow above mine workings is observed at Hallside (c. 10 km SE of Glasgow), where the heat flow through a 352 m deep borehole is c. 14 mW m−2. Similarly, the heat flow across the 199 m deep GGC01 borehole in the Glasgow Geothermal Energy Research Field Site is c. 44 mW m−2. The differences between these values and the expected regional heat flow suggest a significant component of horizontal heat flow into surrounding flooded mine workings. This deduction also influences the quantification of deeper geothermal resources, as extrapolation of the temperature gradient above mine workings would underestimate the temperature at depth. Future projects should consider the influence of historical mining on heat flow when temperature datasets such as these are used in the design of geothermal developments. Supplementary material: Background information on the chronology of historical mining at each borehole location and a summary of groundwater flow in mine workings beneath Glasgow are available at https://doi.org/10.6084/m9.figshare.c.4681100 Thematic collection: This article is part of the ‘Early Career Research’ available at: https://www.lyellcollection.org/cc/SJG-early-career-research

Highlights

Studies of the former NE England coalfield in Tyneside demonstrated that heat flow perturbations in boreholes were due to the entrainment and lateral dispersion of heat from deeper in the subsurface through flooded mine workings
By unravelling the effect of mine workings on the subsurface thermal state, an appraisal of existing geothermal measurements across the city of Glasgow can be made. This enables: (1) a quantification of the potential geothermal resource in the abandoned, flooded mine workings; (2) an assessment of the accuracy of existing subsurface temperature measurements, for example as a precursor to applying corrections to heat flow measurements to account for palaeoclimate and topography (Westaway & Younger 2013); and (3) a more accurate extrapolation of subsurface temperature measurements to greater depths, enabling a quantification of the potential geothermal resource in the underlying hot sedimentary aquifers (HSAs)
To assess the potential of these resources it is crucial to understand the flow of heat in the subsurface. Studies from the former NE England coalfield in Tyneside have demonstrated heat flow perturbations in boreholes to be the result of lateral dispersion of geothermally radiating heat through flooded mine workings

Summary

Introduction

Studies of the former NE England coalfield in Tyneside demonstrated that heat flow perturbations in boreholes were due to the entrainment and lateral dispersion of heat from deeper in the subsurface through flooded mine workings. The heat flow across the 199 m deep GGC01 borehole in the Glasgow Geothermal Energy Research Field Site is c. The differences between these values and the expected regional heat flow suggest a significant component of horizontal heat flow into surrounding flooded mine workings. This deduction influences the quantification of deeper geothermal resources, as extrapolation of the temperature gradient above mine workings would underestimate the temperature at depth. Future projects should consider the influence of historical mining on heat flow when temperature datasets such as these are used in the design of geothermal developments

Findings

Discussion

Conclusion