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Underground gas storage is now regulated by COMAH

29 April 2009

The increasing supply of imported gas in the UK has led to a growing requirement for national storage capacity. To secure an affordable energy supply, much of this requirement is being satisfied by underground gas storage facilities. Gas storage in depleted reservoirs now falls within the scope of the Control of Major Accident Hazards Regulations 1999 (Comah).

Underground gas storage is now regulated by COMAH
Underground gas storage is now regulated by COMAH

Previously, storage has been regulated by HSE under the Borehole Sites and Operations Regulations 1995.

There are two types of onshore, underground natural gas storage facilities currently operating in the UK: man-made salt cavities and depleted oil and gas reservoirs. While both forms of storage require hazardous substances consent, only salt cavity storage sites have been previously subject to the Comah regulations.

Gwyneth Deakins, Head of HSE’s Major Hazards Policy Unit, explained: “Comah’s application in this area is in line with the latest advice from Europe concerning the regulation of underground gas storage. Regulation of this area through Comah will provide the most appropriate safety standards as storage increases.”

A gas storage facility is being planned in the Wyre Estuary at Preesall in Lancashire on the Irish Sea coast. The site could be the largest onshore natural gas storage facility in the UK, with initial working storage capacity of 12 billion cubic feet (bcf) in 2013, increasing to 42 bcf by 2018. The company developing the project, Canatxx, has already had its application to build an underground gas storage site rejected twice. In October 2007, Secretary of State for Communities and Local Government Hazel Blears dismissed Canatxx's appeal against earlier planning permission rejections.

According to energy-pedia news, permission was withheld due to concern over the site's suitability for safely storing up to 2 million tonnes of gas underground at Preesall in Lancashire. The government recognised the need for more gas storage to help bolster supplies on cold winter days. But it said the company had not proved that the geology of the site was suitable and that it would not ruin the Wyre Estuary landscape.

Brine pumping and salt mining has been carried out in the area since the 1870s. In the 1960s, chemical company ICI developed at Preesall one of the first modern salt solution caverns in the world using gas padding to preserve the salt roof, an effect first observed in the 1890s. This is done by injecting sufficient gas into the cavern to maintain a gas ceiling during the washing so the roof salt does not dissolve. This ensures cavern integrity and stability and prevents surface subsidence. Thereafter ICI washed many subsequent caverns at Preesall using this technique.

Canatxx has apparently made sonar surveys of 14 of these relatively modern caverns and reports that they are in stable condition today, over forty years after their creation. However, following the results of a Public Inquiry, local residents say the salt under the Wyre Estuary is severely fractured by faults and many of the proposed sites for caverns are too close to the old brine wells and salt mines which are coalescing and collapsing and is not appropriate to store gas in the quantities which Canatxx is proposing.

The issue of underground gas storage was discussed at the 19th Meeting of the Seveso Committee of Competent Authorities (CCA) where it was concluded that ‘the Seveso II Directive should generally be applied to all such forms of storage, including storage in natural gas fields/strata’. This was confirmed at the 20th Meeting of the CCA in Bordeaux, where it was stated that, as regards underground gas storage, ‘the Commission expects that in the light of the survey and the conclusions at the last CCA the Member States will apply the directive to all such underground storage sites to ensure the same level of safety’. In other words: Comah will now apply to gas storage in both man-made salt cavities and natural strata.

Canatxx is now looking for partners in the gas facility. The task should become simpler now the regulations have been clarified.

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