OR/17/006 Appendix 3 - UK Geoenergy Observatories: Glasgow Geothermal Energy Research Field Site (GGERFS)

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Monaghan, A A, Dochartaigh, B O, Fordyce, F, Loveless, S, Entwisle, D, Quinn, M, Smith, K, Ellen, R, Arkley, S, Kearsey, T, Campbell, S D G, Fellgett, M, and Mosca, I. 2017. UKGEOS - Glasgow geothermal Energy Research Field Site (GGERFS): initial summary of the geological platform. British Geological Survey Open Report, OR/17/006.

Vision[edit]

Note: this section was added in May 2017, some time after the report was written.

Geothermal energy has the potential to provide continuous, sustainable, low carbon and renewable heat (and electricity) to many of the homes and workplaces in the UK. However, this potential baseload contribution to the UK’s energy mix, and to decarbonisation of its energy, is as yet largely unrealised.

The BGS (NERC) UKGEOS project’s Glasgow Geothermal Energy Research Field Site (GGERFS) is intended therefore to provide a greatly improved understanding of the nature, extent, accessibility and sustainability, of some of the UK’s potentially substantial and widespread geothermal resources. The research, data and good practice which GGERFS will provide, could greatly assist sustainable development, and community scales of use, of these resources; either on their own or in combination with other sources of heat available above ground, via district heating networks.

GGERFS is located above an extensive network of abandoned mine workings, developed on multiple levels and to significant depths. The mines are all closed now, and when they did, pumping of water ceased and groundwater reverted to natural levels, flooding the mines, creating opportunities for extraction of heat from the minewaters (e.g. PB Power, 2004[1]; Campbell et al. 2010[2] etc.). This will be a focus of GGERFS research. Sandstones beneath the mine workings also present opportunities for research into their heat potential.

The site therefore has much in common with many towns and villages in Scotland’s Central Belt (Figure 1 below), and elsewhere in the UK with similar mining legacies, and complex Carboniferous geology. Lessons learnt at GGERFS, will be applicable generally across large parts of the UK’s former industrial heartlands.

The research focus
The research agenda of GGERFS will be set by the research community as a whole (public and private sectors), with a Science Advisory Group, comprising geothermal and other sub-surface experts, playing a key role. Engagement with, and involvement of the local community will also be crucial. However, the broad focus of GGERFS research will be to investigate heat potential, and the achievable as opposed to the theoretical yield of heat, from:

- warm waters in the abandoned and flooded (coal) mines, up to 300 m below surface; these are aquifers fundamentally affected by mining (‘anthropogenically-enhanced aquifers’), and
- strata capable of yielding warm to hot waters (Hot Sedimentary Aquifers (HSA)) at greater depths below the mines (hundreds of metres to more than 1 km)

The potential scale of HSA resources depends largely on natural properties of the host rocks — typically sandstones; depth of occurrence; variable thickness, lateral extent, permeability, porosity, and so productivity.

By contrast, minewater heat resources benefit substantially from their man-made characteristics. Permeability has been greatly increased due to the flow pathways created by layer-parallel galleries of coal workings, connecting tunnels, and shafts, and fractures in the surrounding rocks created by the controlled collapse associated with the prevalent long- and short-wall methods of mining. The enhanced permeability makes water easier to abstract and re-inject, and warmer and cooler waters can likely be kept apart in different levels in the mine, preventing mixing, and sustaining the resource.

Traditionally, geothermal resources have been viewed as sources of heat; with temperatures being either high enough for direct use (similar to water temperatures in current domestic radiators), or sufficiently extreme to enable steam production to power turbines and generate electricity. GGERFS will focus however on geothermal resources at relatively shallow depths. Although of lower temperature, these low enthalpy resources are potentially on a large scale, and relatively more available/accessible. The ability to develop these resources on a small scale at least is already proved. Indeed, a small-scale minewater heat scheme has been operating effectively in the Shettleston area of Glasgow (less than 2 km east of GGERFS) for nearly 20 years, and a larger scheme has been operating in the Netherlands (at Heerlen) for 10 years. In addition, the Coal Authority pump waters from mine workings at several locations in the UK to maintain groundwater levels, and abstract heat at some of these. However, the key potential to up-scale schemes such as these, and to sustain flow and productivity of water and heat, and return of cooler waters to the subsurface (using confined open-loop heat pump technology), is still largely unknown, and/or poorly documented, especially in the complex geological and post-industrial environmental conditions which prevail in the UK.

GGERFS is ideally located to address this challenge, as it lies in an area where there is neither active discharge, nor controlled pumping, of the mine waters. Also, as mining ceased 83 years ago, the baseline conditions of the mine waters should be relatively stable (chemistry, temperature, flow, level, etc.), including likely adaptation to the urban heat island effect. Any subsequent changes due to removal/addition of heat should be more readily observable, and monitored over time.

However, there is an even greater opportunity to be explored by GGERFS research; to provide both heating, and cooling to where and when needed, affordably, and ideally in combination with other sources of heat (Figure 1 below). This would entail developing management of heat sustainably below surface and on appropriate scales, including its storage when there is a surplus (seasonal, daily, operational supply and demand), or when cooling is required, so that peak and continuous demands can be met within and between communities.

Figure 1    Eastern Glasgow Conurbation: GGERFS site (Clyde Gateway); spatial relationship of known and potential mining and urban areas; and existing/planned district heating networks. Includes mapping data licensed from Ordnance Survey. © Crown Copyright and/or database right 2017. Licence number 100021290 EUL.

Potential scale(s) of heat storage will depend on scales of sub-surface partitioning caused by, for example:

- natural/geological partitioning, due to;
o    faults/fault zones, their later and vertical continuities, and infill, and hence their behaviour as aquicludes, or conduits
for flow (or both)
o    dykes which act as aquicludes, and
o    the presence of folds (which plunge and doubly-plunge)
- man-made partitioning, due to;
o    the scale and interconnectedness of the mine workings (the extent of the worked coal seams having been controlled by geological faults but breached by connecting tunnels and shafts)

In addition, there is the exciting possibility of using the existing labyrinth of mine workings, and connecting tunnels and shafts, to transfer heat in a controlled way (the mines acting as arteries for water/heat flow) from areas of relative surplus, to those of need. This could obviate some costly district heating surface infrastructure.

The infrastructure, data and modelling
GGERFS will establish arrays of sensors on surface, boreholes (environmental baseline, characterisation/monitoring wells) and one or more geothermal boreholes into the mine workings. A phased approach of borehole installation will be used to test, model, and predict far-field effects of heat extraction, storage and transfer below ground, and to enable high resolution, dynamic and linked models of heat, flow and mechanical responses, to be developed and validated.

All of the boreholes will be equipped with cutting edge sensors to establish baseline conditions, and support systematic sampling and measurements of, for example: geochemistry (isotopes, dissolved gases, hydrochemistry, trace organics); heat in waters; thermal conductivity; flow of groundwater/minewater; discharges if any (including ‘diffuse’ discharges into superficial deposits, and the Clyde); partitioning, and hydraulic and other properties, and so heat productivity, of the mine workings where different mining techniques were used, and differing waste (goaf) and voids generated.

The geothermal boreholes in particular can:

- Test and optimise new technologies, sensors, performance, and operational strategies
- Carry out chemical and heat tracer tests to refine and calibrate models, and
- Trial and monitor strategies (dosing, dissolved gas management, minimise clogging and performance of heat exchangers and injection wells)

GGREFS can address a host of research challenges, such as:

- development of optimal strategies for cost-effective invasive (drilling and sensoring) and non-invasive (geophysical and remote sensing) geothermal exploration to characterise the mined and deeper sub-surface, including potentially productive sandstones
- dynamic modelling, and developing related 2D/3D/4D decision-support tools and guidance to optimise:
o    location and spacing of extraction/reinjection systems for, and
o    scales of development and integration of minewater and associated geothermal systems

Although not directly funded by GGERFS, the facility will also provide excellent opportunities to test and develop aspects of demand-side research, and potential linkages locally and on a wider scale with the many heat related projects, and district heating networks developing in the Glasgow area (Figure 1 above) (e.g. Kyriakis, 2016[3]). This raises the potential to develop a game-changing, fully operational, integrated, and monitored, above and below ground heat management demonstration project as an exemplar to inspire others.

GGERFS can also provide valuable opportunities to:

- test and extend a BGS (NERC)-Glasgow City Council initiative on planning of Glasgow’s sub-surface, avoiding conflicting uses, and stewardship of its sub-surface resources and assets
- develop sub-surface planning of heat resources of varying type, location and depth, extending BGS work on subsurface modelling and uncertainty as the basis for separation zones
- refine licensing, and exploitation of heat resources to address potential conflicts between neighbouring users related to subsurface heat storage and transfer given potential openness of the minewater system

References[edit]

  1. P B POWER. 2004. Shawfair Minewater Project: Scottish National Minewater Potential Study. Job No. 69211a/001.
  2. CAMPBELL, S D G, MERRITT, J E, Ó DOCHARTAIGH, B E, MANSOUR, M, HUGHES, A G, FORDYCE, F M , ENTWISLE, D C, MONAGHAN, A A, and LOUGHLIN, S C. 2010. 3D modelling and related datasets for Urban Development — A case study in Glasgow-Clyde, UK 3D geological models and their hydrogeological applications: supporting urban development: a case study in Glasgow-Clyde, UK in Zeitschrift der Deutschen Gesellschaft fur Geowissenschaften, Vol. 161 pt/no.2, 251–262.
  3. KYRIAKIS, S. 2016. Geothermal district heating networks: modelling novel operational strategies incorporating heat storage. PhD Thesis, University of Glasgow.