Cheshire Geoenergy Observatory construction heats up

The UK Geoenergy Observatory in Cheshire is taking shape: seven of its 21 boreholes are complete and its on-site laboratory is already sampling cores and compiling data.

The Cheshire Observatory, located in the University of Chester’s Thornton Science Park, will provide scientists with at-scale test facilities that can be used to optimise and de-risk a range of subsurface energy technologies, including geothermal energy.

It’s one of two observatories being built as part of the £31 million UK Geoenergy Observatories project led by the British Geological Survey (BGS); the other is in Glasgow.

Construction is being carried out by AECOM, who arrived on site in July 2022. The observatory should be complete and fully operational by late 2023

100m Boreholes Give Unprecedented Look Below Ground

The 21 boreholes at the Cheshire Observatory will provide a variety of functions for scientists and researchers.

Rachel Dearden from BGS, project manager at UK Geoenergy Observatories, explained what’s been installed so far.

“We’ve installed seven boreholes and the eighth is underway.

“The first borehole drilled was in the centre of the borehole array and gave us an opportunity to take core samples ahead of any further drilling.

“Then we moved onto one of our multilevel sampler boreholes, which allow us to sample groundwater in the aquifer at different depths. That’s important so that we can understand how groundwater chemistry varies with depth. Also, when we start heating or cooling the aquifer, we can track how the chemistry changes.

“We then drilled and installed four boreholes with sensor strings that will monitor temperature and electrical resistivity at high resolution.”

The most technicallychallenging borehole for the team so far was the multilevel sampler borehole. This involved threading eight water sampling tubes and wires through 50 mm tubing before lowering the tubing into the ground, all while attaching multiple fibre optic and resistivity sensor cables. The borehole was backfilled with repeating layers of gravel, sand and bentonite, a task that took a number of days.

Dearden explained: “Our next task is to install the ground source heat boreholes, which will allow us to heat and cool the ground. The boreholes will be installed with a 100 m deep U-tube, through which fluid will pass down one limb and up the other, to heat or cool the rock. Fluid will pass through the U-tube, heating or cooling the rock.

“We designed this borehole so that we can measure the temperature at every point along this U-tube. To do this we set AECOM and Silixa the challenge of threading a 200 m long fibre optic cable down one limb of the U-tube, round the bend, and back up the other side. Installing this was quite a challenge, but successful! Once all the boreholes are installed, the temperature change created by these boreholes will be measured by sensors in the other boreholes allowing us to see how the heat plume moves through the aquifer.

On-site scientific testing

The Cheshire Observatory is already providing data from the 100 m deep borehole drilled during the ground investigation stage, which is available to researchers on the project website (www.ukgeos.ac.uk). More data will be released in due course.

British Geological Survey scientists work in the on-site laboratory to examine and catalogue the cores of aquifer material recovered during the drilling process.

Dearden said: “We want to characterise the core in immense detail. We sample it as it comes out of the ground so that the properties measured are as close as possible to those in the ground. The on-site laboratory can sample the rock for its microbiology and geochemistry, and then it goes to BGS headquarters to our Core Scanning Facility.