Construction The Gateway gas storage facility will comprise 19 man-made underground storage caverns which will be created by a solution mining process (‘leaching’) in the salt strata beneath the Irish Sea. This involves cycling large amounts of seawater through a salt formation deep beneath the seabed. Gateway will install a small offshore structure (‘monopod’) above each cavern location. The monopods will be used to accommodate equipment in support of the leaching process during construction (pumps, motors, control systems and ancillary equipment). Two leaching strings (pipe-in-pipe) will be hung from the deck of the offshore structure to facilitate seawater injection and brine discharge. The seawater dissolves the salt, leaving an empty space (‘cavern’) in the strata. The brine resulting from this process is brought back to the surface and discharged into the sea via a disperser unit. The developing geometry of the cavern is monitored using an acoustic device which can map the cavern walls as construction proceeds. The caverns will be connected to an offshore gas ‘ring main’ by a short pipeline with isolation valves. Pipelines and a power cable will connect the offshore facilities to a new Gateway Gas Compression Station located onshore in Barrow-in-Furness. Electrical power to the Gateway facility will be provided via a new cable to be installed at the same time as the offshore pipelines. Operation Salt cavern technology is well proven and has been used for storing gas and liquids for many years. When completed, Gateway caverns will have an average spatial volume of approximately 900,000 cubic metres, providing a facility to store a total of 1.512 billion standard cubic metres of working gas.

During operations, the monopods will simply host the wellhead above each cavern, along with the necessary control and monitoring equipment. The design is based on a principle of minimal intervention and the monopods are expected to require very few maintenance visits.

Safety

Gateway has and will continue to adhere to the highest standards of safety and maintenance during all phases of the project. Safety has been a key parameter during the design phase of the project, to ensure a safe environment for personnel involved in the construction and operations of the facility.

Gateway will also enhance the safety and security of gas supplies to the GB and Irish markets.