Gryphon A - Features and Operational Benefits

ABSTRACT The Gryphon A Floating Production, Storage and Offloading (FPSO) unit has a number of novel designfeatures. These features include a unique hull shape, an anchoring system with thruster-assisted mooring, a sliding bearing turret and a transfers system across the turret based on a drag chain. A simple hose system loads shuttle tankers from cargo tanks with a capacityof 525,000 barrels. Gryphon A has now been in operation in the North Sea for over a year, including one of the worst winters for many years. This operationally tested man y of these features. The technology of FPSOs has developed such that they can be used in man y different environmental conditions. Development of previously uneconomic reservoirs isnow possible because of 10w capital and operational costs of FPSOS. However, costs may be reduced further with effective specifications for FPSO'S This paper describes the operational experience of the Gryphon A FPSO and ho w that experience can be used to develop more cost effective FPSOS. BACKGROUND Gryphon A is a ship shaped floating production, storage and offloading unit (FPSO) located in Block 9/18b in the North Sea. Its location is 200 miles North East of Aberdeen, Scotland. Papers presented at the Offshore Technology Conference in Houston in 1994 (References 1 to 3) describe the ship in detail. In summary (Figure 1), the ship is 257m long and operates in a water depth of 112 m. It is located fifteen hundred meters from a cluster of 12 subsea wells that include production, water injection, gas and aquifer wells. The process facilities can produce 60 MBPD of oil from 80 MBPD of gross fluids. The ship went into production on 14 October 1993 and, since then, has operated extremely well. It has continued to operate throughout several Force 12 storms and has produced oil with a cumulative uptime from first production of over 96% (Figure 2). Production has never been shut down, or reduced, because of the weather. There have been no equipment failures attributable to weather or motion of the ship. Thirty-five tanker lifting have exported over 15 million barrels of crude. With this background this paper outlines, qualitatively, some of the criteria used in designing the Gryphon A facilities and the lessons learned through the operation. SHIP PERFORMANCE The design of the Gryphon A process facilities was based on performance criteria obtained from modeltests. The overriding requirement was for all equipment facilities to remain in operation through a one year return storm. Production equipment was designed to operate with pitch and roll of six degrees(single amplitude), with a pitch period of 14 seconds and a roll period of 12 seconds. Equipment and facilities wererequired to survive and remain operable following a 100-year return storm. Ail structural elements were designed to withstand a ship damage criteria equivalent to a roll of 15 degrees.The flare tower, 41 .4m above main deck level, is positioned at the extreme aft, starboard side of the ship.