Rigs to reef in the North Sea

Abstract

From the Abstract: “At present there are some 150 fixed offshore installations on the United Kingdom Continental Shelf. About 100 of these are in shallow water less than 40 m deep in the southern North Sea and are of relatively light-weight construction, often weighing around 300 tons. Much larger structures are found in the deep water of the central and northern North Sea, where steel platforms in 185 m of water sometimes weigh over 85,000 tons, and concrete gravity platforms can reach up to 650,000 tons.

At present, some 17 years after the first oil find, the production from older and smaller fields is declining. Several platforms are approaching the end of their useful lives and the question of platform de-commissioning is now the subject of activc discussion between the U.K. Government, Department of Energy and Operators. The general problem is not new, and practical experience has already been gained from other parts of the world, particularly the Gulf of Mexico where recently platforms were being removed at a rate of around 30 per year. Many of these are small structures in shallow water near the shore, and can be easily removed in one or two lifts by crane barges. The cutting and removal of the large steel jackets of North Sea platforms will be a much more complex operation, and a very different set of problems must be faced with these platforms. The first will be due for de-commissioning during the period 1991-95, another dozen will become redundant in the following 5 years, and about 60 in the decade after that.”