Borehole arrays

Installation of borehole geophysical sensor arrays in progress

The information provided below dates from October 2017. We are in the process of updating this content. We will issue a full report in the coming weeks. Details of the planning application for the Cheshire Observatory can be found here. If you require up-to-date scientific information to inform research ideas, please contact Andy Kingdon.

Please note that Array 5 will not be undertaken and is not part of our planning application.

The BGS, with support from the Science Advisory Group (SAG), is designing the research infrastructure for the Cheshire energy research field site. The infrastructure is based on arrays of research boreholes capable of observing changes in underground conditions.

Borehole arrays have been designed with consideration for the science objectives set out in the UK Geoenergy Observatories science plan.

The arrays will facilitate observation of and experimentation within the subsurface to support investigation of a range of challenges in energy science and associated technologies. The objective of the arrays is to provide a well-focused research infrastructure at a range of spatial scales and investigation depths. This will enable researchers to undertake experimentation and monitoring of subsurface processes.

The new research infrastructure is needed to address the science challenges identified in the science plan:

  • How fluids, often multiple fluid phases, flow through the rock mass.
  • How the chemical interactions between fluids and minerals modify the fluid flow and mechanical properties of the rock mass.
  • How fluid chemistry can be used to monitor the evolving structure of the rock mass, fluid flow and biological and mechanical processes.
  • How stress changes, either as a consequence of injecting, producing or mobilising fluids, or imposed deliberately, cause mechanical responses.
  • The nature of the subsurface biosphere and how it responds to perturbations caused by fluid flow and mechanical changes.
  • The effect of anthropogenic perturbations in the subsurface.
  • Links and feedbacks between the deep subsurface and the shallow subsurface and surface.

This page provides a brief overview of the proposed arrays for the Cheshire energy research field site. These proposals are draft and are subject to change. The BGS is currently (October 2017) in the process of discussing land-access agreements for the proposed borehole locations. All of the infrastructure is also subject to obtaining planning permission and regulatory approval.

Array 1 — baseline groundwater and surface-water monitoring array

The groundwater and surface-water baseline study will establish the environmental baseline conditions before any research activities begin.

Investigation of groundwater and surface water will require establishment of a borehole and surface sensor network to enable baseline characterisation and monitoring. This will be extended to a future, longer-term programme suitable for detecting environmental changes resulting directly or indirectly from research activities and other (industrial) influences.

The objectives of the groundwater and surface-water monitoring programme are:

  • improve the scientific understanding of the subsurface and near-surface groundwater environments, to assist in shaping future research activities
  • establish benchmark information for a baseline period, against which any future research results can be compared to identify any environmental change(s) resulting from proposed activities
  • facilitate development and application of new sensor technology for environmental monitoring

What will this array look like?

The array will comprise clusters of groundwater monitoring wells at 10 locations spread over an area of approximately 16 km2. Each cluster includes three boreholes at close proximity, drilled to depths of 25 m, 50 m and 100 m. The total number of boreholes in Array 1 is 30.

Where will this array be placed?

The ten locations have been identified around the Ince Marshes area to give the best chance of fulfilling the objectives of the water monitoring programme. They represent a range of conceptual subsurface environments.

Array 2 — baseline seismic monitoring array

Prior to activities at the Cheshire energy research field site, the natural seismic activity must be characterised reliably. Without this, any changes in the spatial or temporal behaviour of small-magnitude events may be obscured by the uncertainties. These data will form the natural baseline against which future seismic activity will be compared and contrasted. Should future seismic activity occur from anthropogenic activities in the Ince Marshes area, the proposed array of downhole seismic tools will acquire high-quality data about these events to report changes in the subsurface.

Seismic data will be acquired continuously (excepting periods of maintenance) to establish a baseline against which the effect of future subsurface activities will be measured. Ongoing baseline monitoring and field-wide research experimentation will continue for the life of the operational project.

What will this array look like?

The network is designed for optimal detection of seismicity on the two main regional faults. It has 20 × 300 m deep boreholes, each hosting a three-component geophone at total depth. Some wells will hold two geophones to improve depth resolution. Additionally, some of the wells will have fibre-optic cable installed, a leading-edge technology that may offer an alternative to geophones, to enable the same data to be acquired by different methods. The wells will be filled completely by cement back to surface.

Where will this array be placed?

We will install a network of 20 seismic boreholes with an average spacing of 1 km. These are distributed across a 4 × 4 km area, centred on Ince Marshes.

Array 3 — deep well

New geological data to inform, refine and test the conceptual geological model will be acquired by drilling a deep well. This well will provide fundamental geological observations and data while drilling, through well-bore logging and offsite testing of samples.

What will this array look like?

A single, deep well (approximately 1200 m), reaching total depth in the Carboniferous Millstone Grit Formation, will be drilled and completed to allow multiple well entry for sensors and sampling. The well will be designed to ensure zonal isolation and well integrity for the lifetime of the project and enable eventual well decommissioning and restoration. Note that this well does not penetrate shale horizons that have hydrocarbon potential.

Where will this array be placed?

The well will be placed in a central location relative to the groundwater and seismic baseline borehole arrays.

Array 4 — multiscale array

The multiscale array will enable hydrogeological and hydrogeophysical characterisation of the rock mass from surface to experimental borehole depth. It will allow subsequent investigation at multiple scales (space and time) of hydraulic, geophysical and geochemical responses to changes induced by controlled experiments and/or industrial activity at Ince Marshes.

A key interest for Array 4 is the investigation of the role that geological faults play as barriers or pathways to fluid flow, both under normal (baseline) conditions and in response to controlled experiments.

What will this array look like?

This array will comprise over 20 boreholes with total depths between 50 m and 600 m, located within an area of approximately 150 × 150 m. The array will be equipped with extensive electrode networks for electrical resistivity tomography (ERT) and other sensor types (e.g. pressure transducers, fibre-optic cable) attached to the outside of borehole casing.

Where will this array be placed?

This array will be placed in a central location relative to the groundwater and seismic baseline borehole arrays.

Array 5 — multiphase research well

This well will enable research into fluid–rock and fluid–fluid interactions for a range of gases and liquids including CO2, water, compressed air and various mixes. The primary focus will be on the effects of fluid/gas injection on the rock matrix over a range of temporal and spatial scales. Innovative research can also be pursued relating to geomicrobiology and geochemistry, as well as engineering perspectives on well-bore construction and integrity.

Rock core will be extracted from the deepest Permian strata to inform future research activities in the well and to enable laboratory-based experiments.

What will this array look like?

This array will comprise two wells. The multiphase research well will reach as deep as 1400 m, while remaining in the Permo-Triassic succession. A second well, for hydrogeological monitoring, will be to approximately 100 m with the primary objective of observing the behaviour of the deep well and to verify its well-bore integrity.

A component well of the baseline seismic array (Array 2) will be located at the same site.

Where will this array be placed?

Due to the necessity of avoiding the local fault zones, the array has to be sited peripheral to the seismic and groundwater baseline borehole arrays, but still within the area of baseline investigation.

Contact

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