ABSTRACT

Operators are taking an increasing interest in deep water fields in the Gulf of Mexico. The reasons include discovery of better prospects and the advent of better, i.e. lower cost, technology for recovering the oil. One of the new technologies contributing to this interest is the deep draft Spar Production System. The first such system is scheduled for installation in September, 1996 at Vioska Knoll 826 for Oryx Energy Company and CNG (The "Neptune" Project). The water depth at VK826 is 1930 feet. This paper will provide a description of the production Spar, its major systems and performance. Particular attention will be placed on the design methodology. Improvements in spar technology being pursued in 2nd generation designs will be described.

INTRODUCTION

A Spar consists of a vertical cylinder which provides buoyancy to support facilities above the water surface. Its stability is derived from the location of its center of gravity below its center of buoyancy. Station keeping is provided by lateral, catenary anchor lines which may be attached to the hull near its center of pitch for low dynamic loadings. Spar Buoy type structures have been used in the ocean before. For example, the Floating Instrument Platform (FLIP) was built in 1961 to perform oceanographic research (Fisher and Spiess, 1963). The Brent Spar was built by Royal Dutch Shell as a storage and offloading platform in the North Sea (Sax and de Werk, 1974). The Brent Spar was used for storage and offloading of oil. The present generation of Spars have the following features:

  • Full drilling and process facilities are housed on a deck supported by the spar.

  • Christmas trees for the wells are at the surface.

  • Rigid steel risers are supported in the centerwell by separate buoyancy cans.

  • Catenary mooring lines may be used for stationkeeping to assist in drilling, completion and workover operations.

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