Carbon tracking

Researchers funded by the US Department of Energy (DOE) are teaming up with European scientists to track injected carbon dioxide (CO₂) in the world’s first and longest running carbon storage operation located at the Sleipner gas field in the North Sea.

The researchers - from the Scripps Institution of Oceanography at the University of California, San Diego, and the Lamont-Doherty Earth Observatory (LDEO) in New York - will conduct surveys on the seafloor to monitor injected CO₂ in the 1km-deep reservoir, where more than 10 million tonnes of CO₂ have been stored to date.

An ocean vessel will position sensitive gravity meters on the seafloor using a ship-tethered remotely operated vehicle that will carry them. Data from the instruments on the seafloor will then be transmitted to operators aboard the ship.

Academic researchers from Scripps and LDEO will collaborate with their Norwegian colleagues from StatoilHydro in the analysis of the results. The project will create approximately eight full-time jobs per year, which will be supported throughout the two-year project.

The technology to be used in the project recognises that, as gas is injected into the sandstone reservoir, the density of the formation is altered as water in the pore spaces is displaced by lower density CO₂.

This density change affects the strength of the Earth’s gravity field. Gravity surveys performed by the scientists at different times provide snapshots of the CO₂ plume migration deep below the seafloor.

Since 1996, about one million tonnes of CO₂ per year have been injected into the Sleipner reservoir.

CO₂ that is produced along with natural gas is separated on the production platform and re-injected into a sandstone formation at a depth of about 1,000m below sea level to prevent venting the gas to the atmosphere. An 80m-thick shale cap rock holds the CO₂ securely in place.