The seawater is replaced by gas under pressure in a process known as dewatering.

Six of the nine caverns at Aldbrough are already storing gas. Leaching at the remaining three caverns has been completed. Testing has been completed at two of those caverns and they are being prepared to accept gas. All three of the remaining caverns should be ready for operation by the summer of 2012.

When fully commissioned, Aldbrough will ultimately have the capacity to store around 330mcm (million cubic metres) of gas. It will have the capacity to deliver gas to the National Transmission System at a rate of up to 40mcm per day, equivalent to the average daily consumption of eight million homes, and the ability to have up to 30mcm of gas per day injected. Aldbrough will provide around 7% of the total gas storage capacity in the UK and around 25% of gas deliverability.

The ownership of Aldbrough is divided between SSE and Statoil (UK) Ltd on a two-thirds/one-third basis. The companies’ total investment in the development and construction of Aldbrough is expected to be around GBP 435 million. The companies have the consent to extend the Aldbrough development, but concluded during 2010 that an investment decision on the extension should be deferred while the UK government develops its gas security policy.