A facility in Algeria that captured carbon dioxide on an industrial scale – and locked it up deep underground – is yielding this lesson for researchers exploring ways to deal with global warming: Select a site with care, because the unexpected can happen.
A new study that aims to explain why sequestered CO2 was moving surprisingly quickly through rock formations beneath In Salah, a natural-gas extraction site in central Algeria. In Salah hosted the second-largest industrial-scale sequestration demonstration project after Norway's Statoil, which has been conducting a sequestration demonstration at the Sleipner field in the North Sea since 1996.
The new study of In Salah's effort identifies the injected CO2 itself as a key culprit. The facility was injecting the unwanted greenhouse gas at a rate that boosted the pressure of the CO2 stored in a sandstone formation more than 6,000 feet below the surface.
The rock either fractured under the pressure or the pressure widened existing fractures, allowing the CO2 to migrate into the first of two layers of denser "cap rock," selected to prevent the gas from leaking to the surface and entering the atmosphere, explains Joshua White, a researcher at the Lawrence Livermore National Laboratory in Livermore, Calif., who studies the flow of fluid through porous or fracture rock.