Process Support and Marine Systems in a Spar Hull: Innovation Meets Regulation

Abstract

This article, written by JPT Technology Editor Chris Carpenter, contains highlights of paper OTC 26040, “Process Support and Marine Systems in the Hull: Innovation Meets Regulation,” by Peter Kitchen, Houston Offshore Engineering, and Scott Murphy, Williams Field Services, prepared for the 2015 Offshore Technology Conference, Houston, 4–7 May. The paper has not been peer reviewed. Historically, the marine systems on a spar are relatively simple. However, attracted to the operational value of having large volumes of storage, particularly for flow assurance of the subsea wells and flowlines during shutdown conditions, the subject-hull design criteria included the capabilities to store (inside the hull) 10,000 bbl of dead oil, 1,000 bbl each of diesel and methanol, and 2,400 bbl of subsea chemicals. The paper traces the development of the project’s process-support and marine systems. Introduction The Gulfstar 1 (Fig. 1) is a spar-based floating production system located in the Gulf of Mexico. The spar has full offshore-processing and measurement capabilities for delivering oil and gas to the export pipelines, which tie into the existing offshore infrastructure. The spar hull is 584 ft long and 85 ft in diameter with a 60-ft hull freeboard. The hull supports an 8,500-short-ton, three-level topside. The hull also supports five initial risers hung off at the riser porch and provisions for four additional steel catenary risers to be pulled in through pull tubes. The spar is held on station by a taut mooring system composed of nine chain/polyester/chain mooring lines arranged in three groups. The spar is fitted with a variable ballast system that uses compressed nitrogen to adjust the seawater level in the four open-bottom ballast tanks. The spar hull also supports process and utility equipment and storage for dead oil, methanol, and diesel in integral (structural) tanks and for flow-assurance chemicals in independent (free-standing) tanks inside the hull.