Borehole arrays

The BGS, with support from the Science Advisory Group (SAG), is designing the research infrastructure for the Glasgow Geoenergy Research Field Site. The infrastructure is based on arrays of research boreholes capable of observing changes in underground conditions.

Phase 1 of the Glasgow Geothermal Energy Research Field Site research infrastructure will comprise of three borehole arrays:

  • Array A: mine water characterisation and monitoring
  • Array B: environmental baseline characterisation and monitoring
  • Array C: seismic monitoring

Please note that in the information below all designs, infrastructure, kit, data to be collected are subject to change.

Array A: mine water characterisation and monitoring

Array A boreholes will measure data from what we believe to be a representative set of mine workings to characterise the mined rock volume and mine water hydrogeology. The boreholes will target two levels of mine workings at drilled depths from around 45 m and 90 m and will likely penetrate different types of abandoned mine workings. Data from the mine water borehole array will inform the design and scope of the Phase 2 geothermal research infrastructure.

The array will allow scientists to study in unprecedented detail spatial and temporal connections and variability within a mined rock volume. The aim of the array is to:

  • Improve the scientific understanding of the subsurface mine water environment (i.e. subsurface flow, heat and fluid connectivity, sustainability of mine water resources, fluid-rock mass interactions) through the collection and interpretation of measured data such as mine water temperature, geochemistry, levels, flow and storativity etc.
  • To characterise initial conditions and provide ongoing baseline monitoring of the mine water hydrogeology, against which any future research results can be compared
  • To provide continuous downhole data and cross-borehole imaging of geoelectrical and temperature properties of the subsurface in order to monitor natural and induced properties and changes
  • Provide open data in easily accessible formats
  • Provide borehole infrastructure to test and optimise new technologies, sensors, performance, and operational strategies. Work to study key uncertainties such as dosing, dissolved gas management and clogging could be undertaken in this borehole array.

Where will this array be placed?

Array A: mine water characterisation and monitoring borehole locations (GGERFS01, 02, 03) along with the recorded extent of Glasgow Upper mine workings from BGS interpretation of mine plan records. Ordnance Survey Licence No. 100021290 EUL.

The mine water characterisation and monitoring boreholes comprise three clusters of two boreholes in the Cuningar Loop. The locations have been chosen to penetrate two levels of mine workings in a triangular arrangement, to characterise the mine water flow at a scale suitable for the heterogeneous geology. Small mapped faults and a coal washout, all within the same larger fault block, are typical of the geology. Different styles of mine working are likely to be encountered – stoop and room and total extraction beneath a sandstone or siltstone/mudstone roof (both possibly collapsed or partially collapsed).

What will this array look like?

Example of Array A mine water borehole. (Please note that this diagram is schematic and not to scale).

At each of the three locations there are two boreholes, each cased and screened within a worked coal seam. Each borehole has an internal casing diameter of 255 mm and will have a 4 mm slot screen of length between 3-10 m (dependent on the condition of the working and fractures above/below; Figure to the right). The shallower borehole will target the Glasgow Upper Coal workings at approximately -40 m relative to OD (c.50 m drilled depth) and the deeper borehole will target the Glasgow Main Coal workings at approximately -80 m (c.90 m drilled depth).

The boreholes have been designed to minimise mixing of mined groundwater from different levels and will allow testing of aquifer properties, temperature-pressure monitoring and groundwater sampling of the particular mined seam. This will provide information to understand connectivity, flow and heterogeneity of the mine water system.

The boreholes have been designed with a relatively large diameter, so that they are suitable to be repurposed as future geothermal abstraction, reinjection and science boreholes. They are suitable for the deployment of pumps and other groundwater equipment.

Electrical resistivity tomography and distributed temperature sensing fibre optic cables are planned to be installed in the bedrock sections of the mine water characterisation and monitoring boreholes.

What scientific instrumentation will be in place?

The mine water characterisation and monitoring boreholes have been designed to allow for the installation of scientific instrumentation including and for groundwater sampling:

  • pressure–temperature transducers
  • multiparameter water quality probes
  • submersible sampling and high flow pumps

Array B: environmental baseline characterisation and monitoring

Array B provides baseline groundwater data allowing researchers to study the groundwater regime. The array and its associated monitoring will allow scientists to characterise spatial and temporal variability of groundwater within superficial deposits and near the top of the bedrock. The aim of the array is to:

  • Improve the scientific understanding of the subsurface and near surface groundwater environment in particular the subsurface to surface interactions and potential risks associated with mine water geothermal research activities by collecting data relating to water geochemistry, temperature, and level
  • To characterise initial conditions and provide ongoing baseline monitoring of the non-mined subsurface hydrogeology, against which any future research results can be compared to identify any environmental change(s) resulting from research activities
  • Meet regulatory requirements for developing any future geothermal activities at the site and provide public assurance
  • Provide open groundwater monitoring data in easily accessible formats

Where will this array be placed?

Array B: Environmental baseline characterisation and monitoring borehole locations. Ordnance Survey data ©Crown Copyright and database rights 2018. Ordnance Survey Licence No. 100021290 EUL

The environmental baseline borehole array comprises five boreholes in the Cuningar Loop area. Three boreholes target intervals within the superficial deposits and two target unmined zones near the top of the bedrock. This distribution of boreholes is designed to monitor groundwater interactions at the mine water borehole sites and to the south of those sites, in the approximate direction of the predicted groundwater flow.

What will this array look like?

Example of Array B environmental baseline monitoring borehole design for a target in the superficial deposits (Please note that this diagram is schematic and not to scale)
Array B environmental baseline monitoring borehole design for a target near the top of the bedrock (Please note that this diagram is schematic and not to scale)

Each environmental baseline borehole is cased and screened at its base in the target interval. The superficial deposits boreholes vary in length from 9m up to 18 m drill length with a 103.8 mm internal diameter casing and a 2 m screened interval across the target depth. The near top bedrock boreholes range between 37m and 48 m drill length with a 150 mm internal diameter casing and a 3-10 m screened interval across the zone of interest.

The boreholes have been designed to allow groundwater samples, levels and temperatures to be obtained providing the opportunity to understand vertical variability in groundwater temperature, chemistry, groundwater head and interactions between bedrock and superficial deposits to be studied.

What scientific instrumentation will be in place?

All environmental baseline boreholes have been designed to allow for the installation of scientific instrumentation including, for example:

  • Pressure-temperature transducers
  • Submersible pumps

Array C: seismic monitoring and cored borehole

Caption?)

The GGERFS seismic monitoring borehole is designed to strengthen the national seismic monitoring network in the urban area, so that any felt earthquake can be detected and located. Reliable characterisation of baseline levels of natural seismicity in the vicinity of GGERFS will allow discrimination of any future events that could erroneously be attributed to geothermal activities at the research site. Without this, in the unlikely event that there are any changes in the spatial or temporal behaviour of small seismic magnitude events, these would be obscured by uncertainties.

This is also the cored borehole for GGERFS Phase 1 that is intended to be open-hole wireline logged.

What will this borehole look like?

Array C: Seismic monitoring borehole location at Dalmarnock (Please note that this diagram is schematic and not to scale)

The seismic borehole will have an internal casing diameter of 76.2 mm to 199 m drilled depth. It will contain a string of 5 seismometers at depths roughly 199 m, 160 m, 120 m, 80 m and 40 m. The core will have a 101.6 mm diameter.

The seismic monitoring borehole is located at GGERFS10 in Dalmarnock. The location was chosen due to the availability of a power and broadband connection and being at some distance from motorways and railways.

The Phase 2 geothermal and science infrastructure will be finalised once the results of the Phase 1 characterisation and monitoring boreholes are available.

More information on the data to be collected from the boreholes

Contact

For more information, please use the UK Geoenergy Observatories contact form.