GEOLOGISTS have cast doubts on plans to store greenhouse gases in a natural underground chamber deep beneath the Moray Firth, saying the area's potential has been overstated.
The Captain Sandstone saline aquifer has been "widely hailed" in recent years as a solution to the dilemma of how to capture the climate-change driving carbon dioxide produced by Scotland's gas or coal-fired power stations.
Previously, experts said the subterranean chasm could possibly store decades worth of industrial output and keep it from entering the atmosphere.
But now new research from Heriot Watt University in Edinburgh suggests the rocky void would be prone to leaks because of fissures along its length, making the exercise pointless.
Scientists now say attention should return to sites where CO2 has been found already, such as oilfields where "exploration disappointments" present a "clear opportunity" for carbon storage.
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Professor John Underhill, chief scientist at Heriot-Watt University, said: "Previous CO2 storage studies have primarily focused on the use of subsurface reservoirs in depleted oil and gas fields or regionally extensive saline aquifers
"Given the perceived scale of the challenge and the amount of CO2 that needs to be sequestered to stabilise or reverse emission levels, the geological focus has largely been on regional saline aquifers because of their lateral continuity, gross rock volume, and large storage capacity.
"However, it is essential that the right site is chosen to prove the potential of this technique and demonstrate that CO2 can be safely stored and will not leak to the surface. Poor site selection and gas leakage will undermine the credibility of geological storage."
The researchers' seismic data found that the aquifer is a continuous, interconnected reservoir which rises to a formation close to the surface known as a 'subcrop'.
The lie of the land is a direct result of the uplift and tilt of the UK's subsurface around 55 million years ago, when it collided with the European tectonic plate.
However, the tilt also means that aquifer is an open system with few barriers to hold light fluids and gases.
It is also thought that the formation is cut by several faults, some of which breach the seal of the Captain Sandstone aquifer and rise to the seabed, increasing the risk of gas escaping.
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Prof Underhill added: "For the past seven years, the Captain Sandstone saline aquifer, which lies buried beneath the Moray Firth, has been widely hailed as having the potential to store between 15-100 years of CO2 output from Scotland's power industry.
"Our research concludes that this is the wrong exemplar to choose because the tilt of Britain leads to it rising to subcrop the seabed with few barriers to arrest gas escape and has caused fault reactivation.
"If leakage occurs, which the geology suggests it will, then the case for CO2 storage will be weakened and potentially undermined.
"We should be focusing attention on sites where CO2 has been found already as that proves that the trap and seal works on geological time scales.
"Although these sites are the exploration disappointments of the oil and gas companies, they present a clear opportunity for carbon storage."
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The paper is published in Interpretation, the peer-reviewed, international publication of the Society of Exploration Geophysics and American Association of Petroleum Geologists.
The research was funded by the Scottish Overseas Research Scholarship Award Scheme (SORSAS) and co-authored by PhD student Gustavo Guariguata-Rojas.
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