Geotechnical Sampling and Survey of Salt Strata

Abstract

FSCL has just completed an exploratory borehole to determine the suitability of ground conditions for the development of the world's first offshore salt cavern gas storage scheme. The facility, for a UK developer, is a series of sub-surface caverns, to be created in the salt strata below the Irish Sea and when built (subject to planning consent and financing), will substantially improve the security of energy supply for the UK and Irish Markets. The paper will review the detailed planning, project risks and bespoke equipment that was needed to produce excellent, 100 mm diameter core recovery down to 865 meters below the seabed.Site investigations to circa 1000 meters below the seabed are possible and cost effective solutions can be offered against the need for oilfield drill rigs. Excellent core recovery can be achieved in salt strata and can be combined with a detailed testing programme to give a total picture of the strata investigated. This may open the door to development of future offshore salt cavern facilities.The return of 100mm core for the full depth of the borehole allowed direct correlation of the site with other land based salt strata core samples. The core samples correlated well with the downhole testing programme data and the result provided detailed characterisation of the geology investigated. The site investigation has provided the necessary information to design the salt storage caverns and moved the project forward from a possibility to a reality. The design of the gas storage caverns has commenced and the cavern construction programme is planned to start in 2010.The caverns will provide an initial working gas capacity of 1,200 million cubic meters, and the storage facility will substantially improve the security of energy supplies for the UK and Irish markets.