OR/19/032 Research infrastructure

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Monaghan, A A, Starcher, V, Dochartaigh, B Ó, Shorter, K, and Burkin, J. 2019. UK Geoenergy Observatories: Glasgow Geothermal Energy Research Field Site - Science infrastructure Version 2. UKGEOS Programme. British Geological Survey Internal Report, OR/19/032.

Overview of science infrastructure

This text describes borehole arrays re-scoped to fit within budget (the planning applications cover a greater number of boreholes).

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

The infrastructure also includes the following science installations and environmental baseline monitoring datasets:

  • Groundwater
  • Surface water
  • Ground motion
  • Soil or ground gas
  • Soil chemistry

The Phase 2 geothermal and science infrastructure will be finalised once the results of the Phase 1 characterisation and monitoring boreholes are available. (Array A: Mine water characterisation and monitoring) to (Surface and near-surface environmental baseline monitoring equipment) provide an overview of the infrastructure, instrumentation and data available for research.

Data generated during the construction and operation of the Glasgow Geoenergy Observatory will be made freely available via an online platform.

Array A: Mine water characterisation and monitoring

Overview

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 to 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 great detail spatial and temporal connections and variability within a mined rock volume. The aim of Array A 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.
  • Characterise initial conditions and provide ongoing baseline monitoring of the mine water hydrogeology, against which any future research results can be compared
  • 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.

Locations

Array A comprises three pairs of mine water characterisation and monitoring boreholes in the Cuningar Loop (Figure 9). 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 (stoop and room followed by subsequent total extraction), beneath a sandstone or siltstone/mudstone roof. In both cases the roof may be partially or completely collapsed.

Figure 9    Array A: Mine water characterisation and monitoring (GGERFS01, 02, 03) borehole locations along with the recorded extent of Glasgow Upper mine workings from BGS interpretation of mine abandonment plan records (location error of the order of ± 5 m). Ordnance Survey data © Crown Copyright and database rights 2018. Ordnance Survey Licence No. 100021290 EUL.

Infrastructure

It is planned that each Array A borehole will be cased and screened within a worked coal seam. The boreholes will have an internal casing diameter of 246 mm and a 4 mm slotted screen section 3–10 m in length (dependent on the condition of the working and fractures above/below; Figure 10). The shallower borehole of each pair 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).

Figure 10    Example of Array A mine water borehole design.

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 re-purposed as future geothermal abstraction, reinjection and science boreholes. They are also 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.

Scientific instrumentation

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

  • Pressure–temperature transducers
  • Multi-parameter water quality probes
  • Submersible sampling and high-flow pumps

Scientific data acquisition

UKGEOS will deliver the following samples and data from the mine water boreholes:

  • Hydraulic head and groundwater temperature and specific electrical conductivity (SEC) — measured via continuously recording, monthly-downloaded pressure-temperature-conductivity transducers, supported by monthly manual groundwater level and conductivity measurements
  • Aquifer properties via pump tests
  • Groundwater chemistry — repeated groundwater sampling campaigns will collect and analyse groundwater samples from the boreholes. Sampling will take place monthly for at least 1 year to establish a baseline. Appendix B - Table of analytes proposed for BGS baseline groundwater and surface water analyses, Table 4 summarises the parameters proposed to be analysed. In addition it is planned to collect samples for geomicrobiology studies, and some additional groundwater samples may be taken to be available for the research community
  • Geophysical logging parameters (cased hole so limited tools: gamma, caliper, probably temperature, conductivity for deepest borehole of each pair)
  • Output from electrical resistivity tomography (ERT) and direct temperature sensing (DTS) fibre optic cables
  • Cuttings samples collected during borehole drilling, together with drilling records and logs

Summary table: Array A borehole infrastructure and planned sampling

Please refer to the overview sampling plan overview (UKGEOS report G0007, available on request from ukgeosenquiries) for more detail on sampling.

Table 4    Summary table for Array A.
Array A
Scientific objective: Mine water characterisation and monitoring
No. of sites and boreholes per site 3 sites each with 2 boreholes (GGERFS 01, 02, 03)
Expected lithostratigraphy at TD Glasgow Upper or Glasgow Main mine working, Middle Coal Measures
Boreholes per site One targeting Glasgow Upper working at c. 45 m and one targeting Glasgow Main working at c. 90 m
Borehole diameter 246 mm ID in bedrock section
Casing Installed: uPVC 280 mm OD through bedrock section, two further casings in made ground and superficial deposits
Expected end use Ongoing sampling, monitoring, testing, possibly geothermal abstraction/re-injection
Rock samples available during drilling Drill cuttings aim to be collected every 1 m
Cored boreholes No
Geophysical logs In deepest borehole at each site through casing — gamma, caliper
Geomicrobiological sampling during drilling No BGS collected samples
Academic fluid and drill cuttings samples requested for geomicrobiology
Gas testing during drilling Monitors for H&S
Drilling fluid sampling during drilling BGS: QC sample each day of returned drill fluid, not analysed unless grouting problems
Academic: settling tank, returned drill fluid
Borehole fluid sampling during drilling Academic: daily requested
Borehole fluid sampling post drilling Academic: after borehole cleaning
Pump testing Pump testing after borehole construction, 2 BGS groundwater samples, and academic samples
Groundwater sampling after drilling BGS monthly samples
Academic: TBC, requested
Permanently installed equipment Data loggers with monthly downloads
Cross-borehole geoelectrical imaging (electric resistivity tomography). Direct temperature sensing cables

Array B: Environmental baseline characterisation and monitoring

Overview

Array B has been designed to provide baseline monitoring data for groundwater within superficial deposits and near the top of the bedrock. The aim of this array is to:

  • Improve scientific understanding of the subsurface and near surface groundwater environment, in particular 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

Locations

The environmental baseline borehole array comprises five boreholes in the Cuningar Loop area (Figure 11). 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.

Figure 11    Array B Environmental baseline characterisation and monitoring borehole locations. Ordnance Survey data © Crown Copyright and database rights 2018. Ordnance Survey Licence No. 100021290 EUL.

Infrastructure

Each environmental baseline borehole will be completed with permanent casing, with a slotted well screen in the target interval (Figures 12, 13). The boreholes in the superficial deposits will be drilled to a depth of 9–18m and completed with a 103.8 mm internal diameter casing, with a 2 m screened interval. The near-top bedrock boreholes will be drilled to a depth of 37–48 m and completed with a 150 mm internal diameter casing, with a 3–10 m screened interval.

Figure 12    Example of Array B environmental baseline monitoring borehole design for a target in the superficial deposits.
Figure 13    Example of Array B environmental baseline monitoring borehole design for a target near the top of the bedrock.

Scientific instrumentation

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

  • Pressure-temperature transducers
  • Submersible pumps

Scientific data acquisition

UKGEOS will deliver the following samples and data from the environmental baseline boreholes:

  • Hydraulic head, groundwater temperature and specific electrical conductivity (SEC) — measured via continuously recording, monthly-downloaded pressure-temperature-conductivity transducers, supported by monthly manual groundwater level and conductivity depth measurements
  • Aquifer properties via pump tests
  • Groundwater sampling — repeated groundwater sampling campaigns will collect and analyse groundwater samples from the boreholes. Sampling will take place monthly for at least 1 year to establish a baseline. Appendix B - Table of analytes proposed for BGS baseline groundwater and surface water analyses, Table 4 summarises the parameters proposed to be analysed. In addition it is planned to collect samples for geomicrobiology studies, and some additional groundwater samples may be taken to be available for the research community
  • Cuttings samples collected during borehole drilling, drilling records and logs

Summary table: Array B borehole infrastructure and planned sampling

Please refer to the overview sampling plan overview (UKGEOS report G0007, available on request from ukgeosenquiries) for more detail on sampling.

Table 5    Summary table for Array B.
Array B
Scientific objective: Environmental baseline characterisation and monitoring
No. of sites and boreholes per site 3 sites with 1 borehole (GGERFS 01, 02, 03) plus GGERFS 05 with 2 boreholes
Expected lithostratigraphy at TD Superficial deposits and near top bedrock (Coal Measures)
Boreholes per site Varies depending on site from 9 m to 44 m
Borehole diameter Two designs: uPVC 150 mm ID in bedrock boreholes. uPVC 103.8 mm ID in superficial boreholes
Casing Installed: Two designs: 165 mm OD in bedrock plus additional casings in superficial and made ground. 113.8 mm OD in superficial deposits plus additional casing in made ground
Expected end use Ongoing sampling, groundwater monitoring
Rock samples available during drilling Drill cuttings aim to be collected every 1 m
Cored boreholes No
Geophysical logs No
Geomicrobiological sampling during drilling No BGS collected samples
Academic fluid and drill cuttings samples requested for geomicrobiology
Gas testing during drilling Monitors for H&S
Drilling fluid sampling during drilling BGS: QC sample each day of returned drill fluid, not analysed unless grouting problems
Academic: settling tank, returned drill fluid
Borehole fluid sampling during drilling Academic: daily requested
Borehole fluid sampling post drilling Academic: after borehole cleaning
Pump testing Pump testing after borehole construction, 2 BGS groundwater samples, and academic samples
Groundwater sampling after drilling BGS monthly samples
Academic: TBC, requested
Permanently installed equipment Data loggers with monthly downloads

Array C: Seismic monitoring and cored borehole

Overview

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.

The seismic monitoring borehole was cored during drilling to provide a record of the Scottish Coal Measures geology (no mine workings were encountered during drilling — see Starcher et al., 2019[1]). This borehole was open-hole wireline logged to profile the bedrock geophysical parameters.

Location

The seismic monitoring borehole is located at GGERFS10 in Dalmarnock. (Figure 14). The location was chosen due to the availability of a power and broadband connection, and because it is some distance from motorways and railways. At this location there are no recorded mine workings on mine abandonment plans; intact coals were confirmed by drilling (Starcher et al. 2019[1]).

Figure 14    Array C: Seismic monitoring borehole location at Dalmarnock. Ordnance Survey data © Crown Copyright and database rights 2018. Ordnance Survey Licence No. 100021290 EUL.

Infrastructure

The seismic borehole has an internal casing diameter of 76.6 mm and has been drilled to a depth of 199 m drilled depth. It contains a string of 5 seismometers at drilled depths 198 m, 156 m, 113 m, 71 m and 29 m. The core diameter is 102 mm (Starcher et al., 2019[1]).

Scientific instrumentation

Guralp Radian broadband seismometers that record 3-component acceleration data were lowered into the borehole via a cable and held in place with hole locks. The seismic data is logged at the surface and telemetered in real-time to the online data portal.

To protect the expensive seismic instrumentation, the borehole will generally not be available for the deployment of other scientific equipment.

Scientific data acquisition

UKGEOS has delivered the following samples and data from the seismic monitoring borehole:

  • Geophysical borehole logging (open hole, planned to include gamma, caliper, temperature, conductivity, density, neutron, resistivity, sonic, flowmeter, acoustic imaging)
  • Rock core
  • Time-dependent core samples for geomicrobiology studies
  • Continuous seismometer data

Summary table: Array C borehole infrastructure and planned sampling

Please refer to the overview sampling plan overview (UKGEOS report G0007, available on request from ukgeosenquiries) for more detail on sampling.

Table 6    Summary table for Array C.
Array C
Scientific objective: Cored, seismic monitoring borehole
No. of sites and boreholes per site 1 site (GGERFS10) with 1 borehole (GGC01)
Expected lithostratigraphy at TD Lower Coal Measures
Boreholes per site One 199 m deep borehole
Borehole diameter 76.6 mm ID in bedrock section
Casing Installed: uPVC 96 mm OD in bedrock section. Plus additional casing in superficial deposits and made ground
Expected end use Seismic monitoring
Rock samples available during drilling Core 102 mm diameter
Cored borehole Yes
Geophysical logs Gamma, caliper, density, neutron, resistivity, sonic, flowmeter, acoustic image
Geomicrobiological sampling during drilling Yes, every 10th metre core samples preserved, plus core barrel fluids
Gas testing during drilling Monitors for H&S
Drilling fluid sampling during drilling BGS: QC sample each day of returned drill fluid, not analysed unless grouting problems
Academic: settling tank, returned drill fluid, twice daily
Borehole fluid sampling during drilling Academic: daily
Borehole fluid sampling post drilling Academic: after borehole cleaning
Pump testing No
Groundwater sampling after drilling BGS and academic samples were taken after borehole cleaning/before wireline logging, plus after the Christmas break. No further groundwater sampling is possible
Permanently installed equipment String of 5 seismometers

Surface and near-surface environmental baseline monitoring equipment

A range of environmental baseline monitoring activities are planned for the research site area, both adjacent to, and in the area surrounding the boreholes. Two illustrations (Figures 15, 16) are given below to give a flavour of the equipment planned.

Figure 15    Image showing the planned research compound at GGERFS01.

This is the site containing the most equipment, including soil/ground gas probe, near-surface scanning lasers for CO2 and CH4 plus an active reflector for InSAR measurements.

Figure 16    Image showing a typical research compound at GGERFS02.

The following sections summarise this infrastructure in more detail.

Ground motion

Overview

Ground motion monitoring in the Glasgow area is designed to detect the occurrence of any instability (subsidence, uplift or stability) of the target area before, during, and following subsurface research activities using Synthetic Aperture Radar (SAR) images, which have been acquired since 1995. The interferometric processing of the available SAR imagery (InSAR) has been designed to provide displacement measurements at different times with millimetre accuracy.

Location of infrastructure

Assessment of InSAR data is ongoing over a much wider area of Glasgow than the immediate borehole sites. To improve the calibration and accuracy of future InSAR data, a passive InSAR reflector will be installed at Site 05 (Figures 11, 17) and an active InSAR reflector will be installed at Site 01 (Figure 15).

Figure 17    Passive trihedral corner reflector for SAR imagery.

Data availability

The data generated from this infrastructure includes:

  • InSAR results on the average ground motion and relative time-series
  • Geological interpretation of the InSAR data in order to identify the extent and origin of any possible ground movement. See Bateson et al. (2018)[2]

Soil/ground gas

Overview

Soil or ground gas [note 1] monitoring will provide baseline data on mine gas risk at key points (e.g. near shafts, faults, where coals come to outcrop, boreholes) to detect any existing mine gas reaching the surface. It will also provide information on gases occurring from artificial ground deposits and from natural soils. The soil gas baseline study will involve a phased programme of work for monitoring/measurement of soil gas concentrations, flux and near-ground atmospheric gas concentrations to establish the environmental baseline before any research activities begin.

Location of infrastructure

Soil gas walkover surveys were undertaken in areas including and surrounding the planned borehole compounds GGERFS01–05 in August 2018, prior to any construction activities on site. Ground gas samples were collected and flux measurements were taken.

Continuously recording soil gas probes are planned for borehole Sites 01, 02, 03, and 05.


Two scanning lasers (Figure 18) are planned for Site 01 for the purpose of continuous monitoring of near surface CO2 and CH4.

Figure 18    Scanning laser (left) and typical reflector (right).

Data availability

Data from the soil gas monitoring probes will be downloaded monthly and made openly available. A continuous, live data feed is planned to be available from the scanning lasers.

Soil chemistry

Overview

A soil geochemistry monitoring programme will characterise baseline conditions and support the future science-based activities. Previous BGS soil surveys (Fordyce et al. 2012) and site investigation reports for inorganic substances and persistent organic pollutants (POPs) have indicated localised contamination of soils in the area.

Two sampling rounds are planned

  • prior to drilling — completed in March 2018
  • after the ground disturbance of putting boreholes in place to establish the pre- operational soil chemistry environmental baseline

Unlike fluid chemistry, soil chemistry does not change significantly over seasonal temporal scales so future sampling is recommended after the facility has been operating for 2–3 years.

The soil quality monitoring programme aims to:

  • improve the scientific understanding of the near-surface environment and interactions with the subsurface in the study area
  • support interpretation of water quality data
  • provide information on ground conditions; help meet regulatory requirements and provide public reassurance

Location of samples

In March 2018, ten samples were collected from 0–20 cm depth from each planned borehole site and from two control sites using locations determined for statistical validity.

Data availability

Laboratory analyses of major and trace elements, pH, total organic carbon (TOC), speciated chromium, persistent organic pollutants (POPs), total petroleum hydrocarbons (TPH), polycyclic aromatic hydrocarbons (PAH) and polychlorinated biphenyls (PCBs) are ongoing. The data will be made openly available.

Surface water

Overview

Monitoring of surface water quality will be undertaken to characterise baseline conditions and so support future research activities. Surface water monitoring will be carried out alongside baseline groundwater monitoring over a minimum 12-month period starting in February 2019.

The aims of the surface water monitoring programme are to:

  • Improve the scientific understanding of the surface water environment and groundwater-surface water interactions to aid hydrogeological model characterisation
  • Establish baseline data on spatial and temporal variability to support the identification of any environmental change(s) resulting from the proposed activities (this could be extended to a future longer-term programme, suitable for detecting environmental change resulting directly or indirectly from research activities and, potentially, other anthropogenic influences)
  • Contribute to the assessment and management of risks associated with geothermal
  • resource development and meet regulatory requirements

Location of samples

Sample locations are limited by the small number of exposed watercourses (many are culverted) and access to them. Figure 19 shows the surface water sampling sites currently planned.

Figure 19    Surface water sampling sites commenced February 2019. Ordnance Survey data © Crown Copyright and database rights 2018. Ordnance Survey Licence No.100021290 EUL.

Data availability

The list of planned analytes is given in Appendix B Table of analytes proposed for BGS baseline groundwater and surface water analyses. The data will be made openly available.

References

  1. 1.0 1.1 1.2 STARCHER V, SHORTER K, BARRON H, BURKIN J, ELSOME J, FELLGETT M, KINGDON A, BARNETT M, and MONAGHAN A. 2019 GGC01 Cored, seismic monitoring borehole — initial data release. BGS Open Report OR/19/021, 14pp. http://nora.nerc.ac.uk/id/eprint/522744
  2. BATESON, L, NOVELLINO, A, and JORDAN, C. 2018. Glasgow Geoenergy Research Field Site-Ground motion survey report. British Geological Survey Open Report OR/18/054.

Footnote

  1. (ground gas -at a depth of c. 80–100 cm, in general providing ground gas concentrations free from atmospheric dilution effects and remaining in the vadose zone).