The UK Geoenergy Observatory in Glasgow, which was set up to research minewater heat energy, is now open for research and innovation. The facilities have the potential to deliver new underground data.
In the UK, it is estimated that one in four homes is located above former coalfields. While historical coal mining across the country has left a legacy of flooded, abandoned mines, these sites could prove critical in helping the UK to sustainably meet its future energy needs.
The government’s recent Powering our net zero future White Paper also references the UK’s first large scale mine energy district heating system in County Durham, putting minewater geothermal firmly on the political agenda.
In this context the UK Geoenergy Observatory in Glasgow, the first of a network of UK Geoenergy Observatories (UKGEOS), plays a critical role.
These observatories are a £31M investment by the UK government through the Department for Business, Energy & Industrial Strategy.
It is hoped they will give scientists a better view of the potential for geothermal heat and help to answer some of the questions that remain about this heat source.
The Glasgow Observatory, established by the British Geological Survey (BGS) on behalf of the Natural Environment Research Council, provides flexible infrastructure for scientists interested in exploring the opportunities and processes of shallow geothermal heat and minewater thermal storage.
The observatory is made up of 12 boreholes that go into flooded underground mine workings across five sites in east Glasgow.
Four sites are in the Cunigar Loop, a woodland park on the south east banks of the River Clyde, and one is less than 1km away in Glasgow’s Dalmarnock district on the river’s north bank.
The boreholes penetrate flooded mine workings, bedrock and superficial deposits at depths ranging from 16m to 199m. They are fitted with sensors which enable the behaviour of warm water in underground mine workings to be observed over time.
The Glasgow Geoenergy Observatory’s science lead Alison Monaghan explains that Glasgow was chosen for observatory locations because it was once the site of some of Scotland’s busiest coal mines.
“Glasgow is also typical of a lot of places in the UK that have old coal mines in that it had a lot of heavy industry and is now an area of urban regeneration”, she adds.
The observatory has drilled environmental baseline monitoring boreholes to track changes in the water chemistry and the physical and microbiological properties below the earth’s surface.
Its different research boreholes enable the observatory to investigate the risks, impacts and processes of a minewater geothermal source and to contribute essential data on the technology.
Cuningar Loop, the observatory’s main site, is underlined by a number of different abandoned coal mine workings that came from the Farme colliery in Rutherglen which closed in 1931.
It is here that five minewater boreholes, fitted with sensors, penetrate the abandoned flooded mine workings at three locations across the park. Due to construction problems a sixth borehole has been repurposed for sensor testing.
At Cunigar Loop there are also five environmental monitoring boreholes. An environmental borehole has been drilled at each of the three locations of the minewater boreholes. The remaining two environmental monitoring boreholes are located together on a separate site in the park. On each of the sites the boreholes are arranged in a straight line 10m apart.
An additional 199m cored seismic monitoring borehole was drilled on the Dalmarnock site.
The Glasgow Geoenergy Observatory’s operations manager Vanessa Starcher explains that the minewater boreholes vary in depth.
“Two of them target the deepest mine working in the observatory, the Glasgow Main, at around 80m to 85m deep. The other minewater boreholes target the shallower Glasgow Upper mine working, which is around 45m to 50m deep”, she says.
The purpose of the minewater boreholes is to test aquifer properties, monitor temperature and pressure and take groundwater samples of minewater.
The environmental monitoring boreholes also range in depth. Starcher says: “Two of them are screened in sandstone above the Glasgow Upper mine working and three are screened in sand and gravel in the upper part of the superficial deposits.”
Those targeting the superficial deposits are in the order of 16m while other boreholes which go into the bedrock are approximately 40m deep.
To capture monitoring data, the minewater boreholes are fitted with numerous sensors “to measure parameters, including electrical resistivity. We’ve also got fibre optic cables attached to the borehole casing, which are providing a temperature profile along the length of the borehole”, says Starcher.
The fibre optic sensors will provide continuous monitoring of baseline variation in minewater temperature, pressure and chemistry. These same sensors can be used to monitor the flow of heated or cooled waters. The electrical resistivity sensor will further provide data on the geoelectrical and temperature properties of the underground minewater environment.
A uPVC casing screen being installed onto a minewater borehole
For the main borehole drilling works, the observatory contracted Bam Nuttall which subcontracted Drilcorp to undertake drilling of superficial deposits and bedrock sections within the Cuningar Loop.
“The boreholes all had a very similar style,” explains Starcher. “The top sections, for which the widest hole measures about 880mm in diameter, were drilled with a piling rig. That was primarily to get through the made ground which is around 10m in thickness across the borehole sites at Cuningar Loop.”
After casing and sealing off the boreholes to isolate the made ground section, the contractor continued to drill down into the superficial deposits using a combination of rotary and direct drilling.
“Once they got it into the bedrock, they set a casing string prior to drilling through the mine working sequence”, says Starcher. “The casing used in the bedrock section was uPVC while the upper two casing strings in the made ground and superficials were both steel. A screened section of casing was positioned across the mine workings. For the environmental monitoring boreholes, the screen was installed across a selection of various rock types.”
After installing the casing, the annulus was grouted up so the only water coming into the borehole was through the screened section at its base.
The most difficult part of the drilling process was coming across a mine working. Starcher explains: “You don’t know what you’re going to encounter when you hit a mine working. It could be a water-filled void, it could be intact coal, it could be packed waste. But when you drill into a void, you might get a lot of fluid loss.
“So there are potential drilling issues to ensure that the mine working is fully sealed prior to drilling ahead. That took quite a lot of work and ingenuity on the part of the drillers to make sure that we had a seal across that mine working before we then drilled ahead again.”
To mitigate problems with casing and annulus grouting the team used a downhole camera to assess “the character of the mine workings to determine if the rock above was fractured or not”, says Monaghan.
She adds that hitting and recognising mine workings that were full of warm water was a real milestone.
“Doing the hydrogeological test pumping and finding that the yields of the water were high enough for people to do research about shallow mine geothermal at the site – was also a significant achievement.”
BGS has test pumped all the boreholes, proving high flow rates of 20 litres per second for five hours with steady temperatures of around 12°C in four of the minewater boreholes.
With borehole drilling and testing completed in 2020, the team is now in the second project phase which involves installing geothermal infrastructure into this borehole system. This is expected to be finished in March 2022 – and then the observatory will be open for research purposes.
The observatory has a range of methods for looking at wider environmental monitoring on the surface and underground.
Along with the seismic monitoring borehole the observatory uses interferometric synthetic aperture radar – a geodetic monitoring technique for mapping ground deformation from space – to “measure ground motion effectively”, says Monaghan.
Details of the Cunigar Loop borehole sites
The team has also carried out survey work regularly on things like soil chemistry and soil gas content from before it started constructing the boreholes. As Monaghan explains, “the observatory is very close to the river Clyde, so we’ve also been conducting a programme of monitoring of the surface water chemistry over time”. The chemical and microbiological analysis helps the team to better understand the effect of temperature variation on the subsurface environment.
Crucially, this environmental baseline monitoring work provides data that can help to inform and reassure the public about minewater geothermal projects, says Monaghan.
She notes that subsidence and fears of groundwater pollution can be concerns, especially for those living in coalfield areas.
She adds: “The UK and other countries have learned how important environmental data is for public acceptance and public engagement of projects like ours. Another part of the observatory is running community and public engagement programmes, but also making our data openly available to help people understand what is happening underground.”
Given the scale and scope of the project, there have inevitably been some challenges. To drill into mine workings the observatory had to get permission from the Coal Authority and secure other permissions from the Scottish Environment Protection Agency.
Because the observatory is a 15 year research infrastructure project as opposed to a more straightforward commercial scheme, getting those permissions took longer.
Providing infrastructure that is flexible enough for different users has also been a challenge, adds Monaghan.
To do this the observatory team has been developing health and safety protocols to ensure that all research can be carried out safely across the site, no matter who is using it.
Monaghan adds that the observatory’s research and innovation infrastructure which has academic and commercial applications is ultimately for the community.
Ensuring that its data is publicly available on the UKGEOS website is a big part of this commitment.
The BGS has released detailed information packs on the Glasgow observatory’s boreholes including drilling logs, borehole construction details and overview hydraulic test data. The observatory is currently working on time series data from downhole hydrogeological data loggers and on its external release.
Looking to the future, Starcher hopes that the observatory will develop “in a way that it can eventually have an impact on the policy side of minewater energy and de-risk it enough so that it can become a commercial entity that is both economic and feasible”. Given its groundbreaking research facilities the observatory seems well on its way to doing so.
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Tagged with: Bam Nuttall BGS Boreholes Drilling geoenergy Geothermal Glasgow Glasgow Observatory minewater UK Geoenergy Observatories
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