The selection of the type of drilling or production platform appropriate to a particular off shore site depends, chiefly, upon the likely severity of the marine environment, the nature of the seabed, and the geotechnical properties of the underlying soils and whether there exists a requirement for on-site oil storage. Although these physical factors have all played important roles in shaping the evolution of offshore structures, particularly in the North Sea, economic considerations and the national preferences of client companies have on occasion been decisive.This paper traces the evolution of offshore oil production structures for the North Sea with particular emphasis on the role played by geotechnical engineering during the conception, design, and construction of some of the largest movable structures in the world.

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The search for oil and gas has already extended to the Arctic areas of the world. To date conventional sand islands have been used for exploration drilling purposes in water depths of up to 43 ft. In deeper water exploration has only been possible using floating drilling equipment which can only operate during the short summer season of open water. This paper briefly outlines the geotechnical principles and development to date of hydrostatically supported sand islands. This construction technique, which utilizes hydrostatic water pressure to stabilize dredged sand at near vertical underwater slopes, would allow sand islands to be quickly and economically built in water depths of up to 200 ft. The hydrostatically supported sand island is a gravity structure and, therefore, is only suitable for use on competent seabed soils. This paper presents two different designs which are currently proposed for use as drilling structures in such areas as the Beaufort Sea. One design is intended for use as a movable exploration structure and the second for a permanent production island that would remain on location for 30 to 50 yr. The near vertical side slopes of the hydrostatically supported sand islands reduce the amount of sand required to manageable amounts, and allow the construction on location to be safely completed during the short Arctic summers. The sand provides sufficient mass to resist ice pressures.