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Cosmic rays could help monitor storage of carbon dioxide

High-energy particles from outer space known as cosmic rays could help monitor carbon-dioxide storage sites, according to a group of UK researchers.

A team led by Durham University plans to develop technology that maps the presence of CO2 captured from power plants and injected into underground deposits, by measuring how well they absorb sub-atomic particles created by cosmic rays striking the Earth’s atmosphere.

These particles, known as muons, are better at penetrating some substances than others, and so the team of scientists and engineers believes it can map the CO2 in a deposit by using sensors to count how many muons pass through it as they fall from the sky.

Project leader Prof Jon Gluyas of Durham’s earth sciences department told The Engineer that the technique would add to and improve existing methods of checking CO2 deposits because it would allow constant monitoring.

‘If we’re to store CO2 deep beneath the Earth’s surface, we need a suite of robust monitoring techniques,’ he said. ‘At the moment the primary one is time-lapse seismic, where you take a seismic survey and repeat it annually as you inject the CO2.

‘You’ve got to go out and actively take the survey and the only information you get is when you shoot it. And the ballpark costs of the survey are £1m a go. We’re trying to look for a passive monitoring scheme and the advantage of using muons is that they’re always switched on.’

Muons are tiny particles similar to electrons that are created when cosmic rays collide with molecules of oxygen and nitrogen in the atmosphere, and then fall to Earth.

They can penetrate deep into the planet’s surface and have even been detected in mines, including at the Boulby mine Deep Underground Science Facility in Yorkshire run by the Science and Technology Facilities Council (STFC), where the scientists will test the new technology.

One of the main ways the energy industry believes it can reduce CO2 emissions from power plants is by capturing the greenhouse gas and injecting it into sub-surface rock formations, often deep below the seabed.

When the CO2 is injected into the rock it displaces the salt water trapped there. As the CO2 absorbs far fewer muons than the water, placing sensors below the deposit should allow the scientists to determine whether there is CO2 in the rocks above.

‘We believe we can detect about a four per cent change at a depth of 1km,’ said Gluyas. This could allow continuous monitoring of the deposits as CO2 is injected, providing an early-warning signal if the gas doesn’t appear where it should or begins to move.

The sensors would be deployed at the end of horizontal tunnels drilled outwards from the bottom of the injection well, positioning at different points below the rock formation that absorbs the CO2 as it passes down the vertical well.

The researchers, which include participants from Sheffield, Bath and Newcastle universities and from NASA’s Jet Propulsion Laboratory, say the sensor technology already exists but would need to be made more robust for use underground.

‘We’re taking a piece of technology that is known to work in fairly benign settings and developing its robustness for a rather more exotic one, but we’re replicating the sorts of technology styles that are used for oil and gas production,’ said Gluyas.

‘We need to develop the technology that would allow transmission of the data but again we can borrow from the oil industry. There is a whole array of technologies that allow you to transfer measurements, some are transferred through fluid in the well wall, others are electrical and so on.’

The three-year project is co-funded by £647,000 from the Department of Energy and Climate Change (DECC) and matched funding from industrial partners, which include Premier Oil & Gas and Cleveland Potash.

The DECC grant is part of a larger £18.5m stream of funding for innovative carbon capture and storage (CCS) projects, which itself comes from the government’s four-year £125m CCS R&D programme.

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