Wednesday, May 6, 2009

Problems with CO2 Sequestration in North Sea

Leakages in the Utsira formation and their consequences for CCS policy

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The Sleipner CO2 project in the North Sea is one of only three large-scale CO2 storage projects worldwide. The oldest in operation, Sleipner has been injecting about 1 million tonnes of CO2 into a sub-seabed saline aquifer since 1996. Carbon capture and storage (CCS) proponents point to Sleipner as proof that CO2 can be stored safely and permanently while heralding the Utsira formation, that it is a part of, as large enough to hold Europe’s emissions for years to come. However, recent developments in the North Sea indicate otherwise:"

"What’s more, unpredicted movement of injected CO2 has been observed in the reservoir and so far has not been satisfactorily explained by any reservoir geologist.

When the Sleipner project began in 1996, CO2 was expected to rise gradually through the layers of the formation once it was injected underground. However, seismic imaging has shown that the CO2 is instead flowing almost immediately to the top of the formation - moving up by more than a hundred meters per year.

As described in a recent article, this demonstrates that the mudstones present in the formation were not serving as a barrier to the vertical CO2 movement, as scientists had originally expected. Additionally, it indicates that the geological characteristics of the formation may have been altered by the injected CO2

17. A more disturbing possibility is that much less CO2 is being stored in the formation than estimated, meaning that CO2 is leaking at an unknown rate18,19. While this is currently peculative, leakage rates at any level are of interest. Even very low annual leakage rates, as low as 0.1 percent, could undermine potential climatic benefits of geological storage on a time scale of a few centuries

20. As mentioned, it is currently not possible to detect CO2 leakages in these small volumes. While StatoilHydro acknowledges this, they argue that the above ceiling structures are nevertheless safe enough to prevent leakage into the external environment."