Ninian Field Concrete Gravity Platform

Abstract The Ninian Central Platform was built at Loch Kishorn by Howard-Doris for Chevron (UK) Ltd. The paper discusses the design process together with the construction methods. Special emphasis is given to the maximum flexibility of the construction stages to optimise the overall construction duration by using various slipforms and extensive prefabrication. Emphasis is also given to the Kishorn prefabrication. Emphasis is also given to the Kishorn Construction Yard and Facilities and to versatility to place modules eccentrically on the deck owing to the high resources of differential ballasting. Introduction The Ninian Central Platform will form the main base for the drilling and production of oil from the Ninian Field in the northern North Sea. The platform was built for Chevron Petroleum (UK) Ltd. by Howard-Doris Ltd. at their construction yard in Loch Kishorn. To build this platform, the largest concrete offshore structure so far constructed and the fourth designed by Howard-Doris, a new platform construction complex was designed and built by Howard-Doris on the northern shore of Loch Kishorn on the West Coast of Scotland. The concrete gravity structure was built during the years 1975 to 1977. After the deck mating by the end of November 1977, the placing of modules and hook up was carried out from December 1977 to April 1978. The concrete gravity structure was successfully set in place on May 17, 1978, the displacement of the structure at towing being 600,000 t. DESCRIPTION OF THE STRUCTURE The structure stands on a base slab 140 metres diameter, its general external shape (see fig.) is cylindrical with a progressive stepped reduction in diameter from the base to the breakwater wall (diameter 45 metres) which rises from 75 metres to a level of 149 metres above the sea bed. The deck structure and modules are supported by two concentric cylindrical walls. The outer of these walls, the breakwater wall, takes the majority of the vertical loading from the deck. Its large diameter provides the possibility of many support points over provides the possibility of many support points over a large area thus reducing the deck cantilever. The wall is a patented Jarlan perforated breakwater design. P. 241