North Sea

Carbon dioxide storage is secure

The Sleipner gas field in the North Sea has the world's first purpose-engineered subsea geological storage site for carbon dioxide. Contrary to your headline's implication, seabed fractures do not pose any threat to this project (Nature 504, 339–340; 2013).

Independent researchers have analysed extensive data from site monitoring using seismic-reflection surveys of the deep subsurface (both before CO2 injection and then at two-year intervals); they found that performance is excellent, with no evidence of any CO2 leakage (see A. J. Cavanagh and R. S. Haszeldine, Int. J. Greenh. Gas Con. 21, 101–112; 2014).

Your graphic, which juxtaposes stored CO2 with fractures, is also misleading: Sleipner is in fact 25 kilometres away from the fracture described and is overlain by 500 metres of sealing mudrock from the estimated depth of the crack. Elsewhere beneath the North Sea, mudrocks have retained natural CO2 for tens of millions of years.

The suggestion that leakage would be “a disaster for public opinion” is unsupported. Social-science research indicates that unintended leakage need not be a show-stopper (see L. Mabon et al. Mar. Policy 45, 9–15; 2014). More than guarantees that sites will never leak, the public seeks reassurance that site selection minimizes leakage risk, and that monitoring and remediation procedures are in place should a leak be discovered.

There are many known fluid conduits beneath the North Sea, but there is no evidence of unplanned CO2 or methane movement in the rocks overlying the storage site. Since the Sleipner project was set up 20 years ago, global endeavours have improved the geoscientific identification, operation and monitoring of CO2 storage (see V. Scott et al. Nature Clim. Change 3, 105–111; 2013). Sleipner's CO2 is securely retained by residual saturation in the reservoir, multiple mudrock seals, and eventual dissolution and dispersion in pore waters.

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Correspondence to Vivian Scott.

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Scott, V. Carbon dioxide storage is secure. Nature 506, 34 (2014).

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