Ancient reservoir holds clues to help climate change technology

Efforts to combat climate change could be boosted by insight gained from an ancient carbon dioxide reservoir in the US state, Utah.

Studies of the site, where tiny amounts of naturally generated CO2 gas have risen to the surface over the past 400,000 years, could help scientists develop safe methods for carbon capture and storage, in which the greenhouse gas is collected from power stations and stored in rocks deep underground.

Researchers studied leakage from a natural underground reservoir of CO2 cut by two geological faults near Utah's Green River.

By examining deposits of natural travertine – a type of limestone – formed at natural CO2-rich springs over hundreds of thousands of years, they were able to map where leaks had occurred and calculate volumes and rates of leakage over time.

Professor Zoe Shipton, from the University of Strathclyde's Department of Civil and Environmental Engineering, says, ''This study gives us a remarkable record of how and where CO2 and water have moved up a geological fault zone over the last 400,000 years.

"The results are not just important for future CO2 storage sites, but will help us understand how metals such as gold accumulate in deposits along fault zones, and how faults can act as barriers or conduits to flow of other fluids such as hydrocarbons and waste water.''

The study found that leaks from geological fault zones are more intense than leaks from the rocks through which the faults cut. They also found that man-made leakages, such as from abandoned oil wells, transmit higher volumes of CO2 than natural faults in rock.

Scientists say the study's long history of leakage through natural faults, and its finding that the leakage is concentrated in specific points along the faults, will help inform the design and monitoring of sites developed for storage. They also point out that that the wells in this study were abandoned without regard for CO2 leaks, and modern wells are much more carefully managed.

Their findings concur with results from recent fracking research, which indicate that well integrity represents the biggest risk to shale gas operations. The work also gives valuable insight into the impacts of leaks from well bores.

Dr Neil Burnside, of the University of Edinburgh's School of GeoSciences, said: ''Studying an ancient natural CO2 reservoir has given us enormous insight into how man-made storage sites could behave in the long term. This work further highlights wellbore leakage is the largest risk to geological storage projects.''?

Scientists from the Universities of Edinburgh, Glasgow, Strathclyde and the Scottish Universities Environmental Research Centre carried out the work, which was published in the journal Geology and funded by the Natural Environmental Research Council.