OR/19/052 Physical sample collection and related data acquisition
|Kingdon, A, Fellgett, M W, and Spence, M J. 2019. UKGEOS Cheshire Energy Research Field Site - Science infrastructure. British Geological Survey Internal Report, OR/19/052.|
Contributors: Midgley, J, Elsome, J W, Dearden, R A, Chapman, C, Burke, S P, Hough, E, Luckett, R R, and Bianchi, M.
It is envisaged that a large amount of physical samples and data will be collected during drilling and immediately post drilling. This section reviews the types of samples and data that will be acquired by the UKGEOS programme. Under the terms of the NERC data policy all samples and data that derived from them must be archived within the relevant data repository. The NERC National Geoscience Data Centres (NGDC) and Nation Geological Repository are the designated data centres for deposition of earth science digital data, and physical samples respectively. Both facilities are located at the British Geological Survey at Keyworth.
The data policy states that publicly funded data must be made openly available. However the policy allows of a moratorium period with unique access for scientists to undertake their research of up to 2 years post acquisition to complete research. After that moratorium period all samples and derived data will be openly available to all scientists. All digital data will be added to the UKGEOS website; data portal as fast as is proactively possible. Digital object identifiers (DOIs) will be issued to some of the data to allow for the tracking of outputs. Scientists that are free to publish this research but this must be on a journal which complies with the UK’s open-access publication rules. Thereafter materials and the data therefrom will be available to all researchers who wish to undertake research relating to UKGEOS.
During drilling, a wide range of operational data will be collected which will vary between arrays. A maximal set may include: driller’s logs, leak-off test, drilling parameters, drill fluid logging and when complete, a well deviation survey.
Core material will be the primary resource for characterising the geology across the study area. The focus on core recovery is acquiring representative core from all encountered stratigraphic sections. This will include: the Quaternary, Permo-Triassic sandstones and underlying Carboniferous succession. The expected stratigraphy of the Carboniferous section consists of: the Warwickshire Group, Pennine Coal Measures Group and Millstone Grit Group.
In total, core will be retrieved from:
- Array 1 – 5 x 100 metres deep boreholes
- Array 2 – 4 x 200 metres deep boreholes
- Array 3 – 1 x 1200 metres deep borehole
- Array 4 – 1 x 600 metres borehole (includes core taken directly through the fault zone) and 3 x 100 metres boreholes.
The core will be sampled for microbiological analysis on site and then returned to BGS Keyworth. To facilitate biological sampling, tracers will be added to drilling fluid to assess contamination of samples. Fluorescent microspheres or other chemical tracers will be used for the assessment of infiltration of drill mud into the sample core.
The core will be logged for lithology and fractures, and described and interpreted. This will provide detailed insight into the stratigraphic evolution of the area and the depositional environments resulting in the lithologies and fluids represented in the subsurface.
Where possible, core will be scanned using the full suite of core scanning equipment documented in the annex below. Physical core will be analysed for a wide range of microbiological, geochemical and geomechanical properties. The core will be made available for researchers to undertake further sampling and analysis. All data will be available openly.
The core material will be stored in the NGR, where it will be available through normal procedures for researchers to view and undertake further sampling/research.
The core acquired while drilling the infrastructure is the primary dataset for the first stage of the project. The only way to directly investigate the subsurface is by analysing core material, and the fluids contained therein, and the only chance to acquire core from these boreholes is during their drilling.
At the Cheshire Energy Research Field Site, the focus is on acquiring representative core from all encountered stratigraphic sections across the footprint of the CERFS site. Many CERFS sites will prove Quaternary successions and although all boreholes prove Permo-Triassic sandstones (which are a principal aquifer in this area), boreholes associated with Site A, including Array 3 and the deeper boreholes in Array 4, will also prove parts of the underlying Carboniferous succession including the Warwickshire Group, Coal Measures and Millstone Grit groups.
The provisional coring plan for bedrock and superficials is detailed in Tables 3 and 4, respectively.
|7 x 100 m||Groundwater baseline boreholes||Array 1|
|6 x 200 m||Seismic boreholes, plus the upper 50 m of one 300 m deep seismic borehole (for retrieval of Quaternary material only)||Array 2|
|1 x 1200 m||Deep borehole, from 0 — or as close as practicable — to TD||Array 3|
|1 x 600 m||1 x 600 m + 2 x deepest 200 m||Array 4|
|3 x 100 m||From the multi-scalar array||Array 4|
|Total rock core||4000 m (planned)|
|Superficial Core Acquisition|
|c. 2 x 24 m — to top bedrock||Baseline Groundwater||Array 1|
|c. 2 x 30 m — to top bedrock||Baseline Groundwater||Array 1|
|c. 2 x 34 m — to top bedrock||Baseline Seismic||Array 2|
|c. 2 x 21 m — to top bedrock||Baseline Seismic||Array 2|
|c. 2 x 21 m — to top bedrock||Baseline Groundwater||Array 1|
|c. 2 x 12 m — to top bedrock||Deep well (at Site A)||Array 3|
|Total superficials core||284 m (planned)|
Rock core will be processed in Keyworth to generate sedimentological, fracture and engineering logs, which will then be correlated with associated down-hole geophysical logs (including image logs), and geochemical and geophysical data.
Basis of bedrock core acquisition
The core recovery plan has been developed taking into account the need to recover representative material from major structural and stratigraphic features. The stored core will be preserved at the National Geological Repository at BGS Keyworth as a resource for future research.
The stratigraphic range is given by Permo-Trias boreholes TH0401, TH402 and TH403 (i.e. the ca. 600 m wells in Array 04) and TH0301, which is prognosed to give the complete stratigraphy in the central part of the site from Permo-Trias to Millstone Grit;
Additional Permo-Trias stratigraphy is given by:
TH0101, TH0212, TH0107, TH0209, TH0216 (Horst block; younging southwards), with information in the Kemira Graben given by TH0104 (Site N) and TH0125 (Site F). TH0128 (Site G), TH0202 (Site K) and TH0116 (Site D) are located in the Elton Graben. TH0122 Site E is located in the central area of borehole arrays, located immediately to the west of the Dungeon Banks Fault Zone.
Structural features within the Dungeon Banks Fault Zone are given by (in addition to TH0403):
TH0405 Site A 100 m well, TH0412 (100 m well) and TH0415 (100 m well). These boreholes give a broadly east-west profile through the lower part of the Dungeon Banks Fault Zone.
Detail on the composition within the Proto-Hornsmill Channel is anticipated to be gained from locations:
TH0104 (Site N), TH0125 (Site F), Site A, TH0122 Site E, TH0216 Site M, which together give a series of data points extending from the offshore to onshore expression of the mapped position of the channel. Other cored locations will give information on the intra-channel high in the area around Holme Farm in the north to Hapsford in the south.
Spatially, the cored boreholes are spread across the entire site, and importantly include provings within both the Kemira and Elton grabens, which are anticipated to inform the deep geological model for these areas of poor near-surface seismic reflection data. The borehole core retrieved will allow the near-surface interpretation of the ground model to be improved, especially in areas where the near-surface seismic imaging is poor. Along with other legacy core material held by BGS, and downhole logs generated by this project and others held by BGS, it is anticipated that it will be possible to identify, to at least Formation level, the near-surface sandstone units within the Sherwood Sandstone Group and older Permo-Triassic sandstones.
The core will be described and interpreted to provide detailed insight into the stratigraphic evolution of the area and the depositional environments resulting in the lithologies and fluids represented in the subsurface.
The core will provide data on the geometry, character and properties of the Dungeon Banks Fault Zone, in the area of Site A specifically, and variations within the shallow Permo-Triassic in general, across the area of investigation.
Microbiological sampling requires a network of boreholes to understand spatial variation and connectivity. Samples will be taken from all horizons, ideally with samples from each horizon including different boreholes to explore spatial variation of microbial communities. Where possible, sampling will be carried out in boreholes fitted with in situ chemical sensors and those with the capability for in-situ perturbation experiments.
Approach to uncored sections in boreholes
For boreholes where core is acquired, a wider range of logging tools will be run to a higher resolution. Where no core is obtained from boreholes basic wireline logs will be obtained from the deepest borehole or one of the deepest boreholes at the site.
Additionally, 50g of bagged and labelled cuttings will be collected at 1 m intervals of any uncored section of Array 03 or at the request of the BGS geologist/BGS Technical Manager.
Cuttings (50g of bagged and labelled cuttings) at 1 m intervals will also be collected from Site J (TH0210) and Site L (TH0214), as these sites are not in the coring plan.
Basis of superficials core acquisition
Sampling locations have been identified that:
- Characterise the Quaternary deposits — to help understand potential flow paths and infiltration paths to bedrock
- Supply material to analyse in order to improve the shallow geophysical and conceptual site models (CSM), allowing geology and physical properties to be correlated and interpolated between boreholes
- Supply material to investigate Carbon-cycling in the near surface
- Supply material to analyse Palaeoenvironmental reconstructions
- Supply material to analyse Aromatic hydrocarbons in the near surface — including contaminants in estuarine environments
To satisfy these objectives, six locations for sample retrieval have been identified from CERFS sites A–N. Sites have been identified that are located near to lines of shallow geophysical investigation that was carried out during 2018 (gravity, seismic reflection, passive seismic, ERT).
Unconsolidated material from the Hornsmill Channel will be retrieved from Site F (TH0126) in sealed liners that will be refrigerated at site. Approximately 25 m of samples are anticipated.
Additional sediment core samples will be retrieved from sites A, N, K, L and C. The wells will be cored as twin sets at each location i.e. cored twice in close proximity. One core will be available for destructive testing by the BGS and research associates to generate a digital dataset, with the second twin core retained for future research projects.
In priority order, the following sites have been identified for superficials core collection (Figure 15):
Site A: (data may be forthcoming at Site A from geotechnical site investigation): located on western end of south-east shallow geophysical line. Site A is anticipated to prove ~12 m of Tidal Flat deposits/Peat overlying 5 m of Glaciofluvial Sand and Gravel on ~7 m Till (24 m Quaternary Deposits in total). This area is on the western end of the shallow geophysical line and core retrieved from this location would allow validation and calibration of derived physical property models and methods, knowledge of the ground conditions and risks (e.g. soft wet ground, running sand, sub-artesian groundwater, surface flooding) at this deep drilling site. This site may also have a borehole heat exchanger installed for thermal response tensing (TRT) and a ground source heat pump (GSHP) for heating the above ground infrastructure. Samples collected from this location will enable engineering geology and physical property testing, including lab thermal conductivity and diffusivity testing, to be performed to improve/confirm the GSHP system design, reduce uncertainty in interpretation of monitoring data (A-DTS, ERT). Coring at this site will add significant scientific value and will enable meaningful parameterisation of thermo-hydrological-mechanical models and conceptual site models that will be developed over the 15-year lifetime of the project.
Site C: located near western end of central west shallow geophysical line (note-Made Ground may be associated with this site). Site C is anticipated to prove ~4 m Made Ground overlying ~3 m Tidal Flat deposits resting on ~5 m Till (~12 m Quaternary Deposits/Made Ground in total). Core sample will enable validation and calibration of the shallow geophysics and improves methods for subsurface attribution.
Site F: located on the eastern end of south-east shallow geophysical line. Site F is anticipated to prove ~9 m of Tidal Flat deposits/Peat resting on ~21 m of Till (~30 m Quaternary Deposits in total). Core sample will enable validation and calibration of the shallow geophysics and improves methods for subsurface attribution. Continuous Dynamic cone penetration test profiles at these sites (off set from the holes by 2–3 m) would also be useful to characterise the strength/stiffness profile of the ground.
Site K: located on the western end of northern shallow geophysical line. Site K is anticipated to prove ~11 m Tidal Flat deposits resting on ~10 m Till (~21 m Quaternary Deposits in total). Core sample will enable validation and calibration of the shallow geophysics and improves methods for subsurface attribution.
Site L: located on western end of south-west shallow geophysical line (note- Made Ground may be associated with this site). Site L is anticipated to prove ~4 m Made Ground overlying ~8 m Tidal Flat deposits resting on ~9 m Till (21 m Quaternary Deposits/Made Ground in total). Core sample will enable validation and calibration of the shallow geophysics and improves methods for subsurface attribution.
Site N: located on the eastern end of central east shallow geophysical line. Site N is anticipated to prove ~4 m of Tidal Flat deposits/Peat overlying ~30 m of Till (~34 m Quaternary Deposits in total).
Collectively, sites L-A-F-N give a transect into the estimated position of the proto-Hornsmill buried channel feature and will help define its depth, geometry and infill, and hence its permeability and the groundwater regime.
Target intervals for wireline rock core recovery
The target intervals for CERFS core recovery, together with summary borehole data, are presented in Table 5 below.
|Site||Array||Use||Asset Code||Hole Depth||Cored interval top (m)||Cored interval base (m)||Core acquired (m)||Comments|
|A||4||Multiscale||TH0401||600||0||600||600||Core interval will be dictated by actual fault geometry|
|A||4||Multiscale||TH0402||600||400||600||200||Core interval will be dictated by actual fault geometry|
|A||4||Multiscale||TH0403||600||400||600||200||Core interval will be dictated by actual fault geometry|
Geophysical wireline logging
Geophysical logging will provide a framework for geological modelling of the study area. The geophysical log data will allow cross-hole stratigraphic correlation and thus structural correlation between the cored and drilled boreholes. A suite of geophysical logging techniques will be applied across the study area (outer array), with more detailed logging being undertaken in the deeper boreholes (inner array).
In the outer array, thirteen cased boreholes (3 x 100 metre, 7 x 200 metre and 3 x 300 metre) will be logged with gamma-ray and caliper tools to allow for stratigraphic correlation.
Within the inner array, the 1200 metre and 1 x 600 metre deep wells will be logged using a highly detailed logging suite. Logging tools will include temperature, spectral gamma ray, density/neutron, Laterolog/induction resistivity suite, full waveform sonic log and 4-arm caliper. In a small subset of wells borehole imaging tools will be run alongside ultrasonic imaging and cement bond logging. In addition, check shots will be undertaken. The logging programme in these wells will be of sufficiently high quality to facilitate a complete interpretation of this succession.