Liuhua 11-1 Development-Design and Fabrication Considerations for Nanhai Sheng Li for the FPSO

Abstract

Abstract This paper describes the development, design, and fabrication of the crude oil process facilities, and the conversion of an existing tanker for use at the Liuhua 11-1 Field. Over a 16-month period spanning 1994 and 1995, Amoco Orient Petroleum Company, and partners, China Offshore Oil Nanhai East Corporation (CONHE), and Kerr-McGee China Petroleum Ltd., converted a crude oil tanker originally built in 1975 to the Nanhai Sheng Li, the floating production, storage and offloading (FPSO) facility for the Liuhua 11-1 Field, The FPSO will process up to 65,000 BOPD produced from 20 subsea wells located 1.7 miles away. In addition to the processing facilities for produced oil and water, the FPSO has a processed crude oil storage capacity of 715,000 bbls. The ship's propulsion system was removed during the conversion, because the FPSO is permanently moored at site by means of a lo-point, 'soft' mooring. The mooring system was designed to survey the 100-year-retum-period typhoon. Several unique aspects of the ship's conversion process facility, and mooring system design are discussed. Process design aspects include the flexibility to accommodate wide variations in produced water-oil ratio and total volume, the design considerations of the large water and crude processing equipment, vessel motions during operation, and equipment survival during storms. The FPSO design discussion focuses on global hull strength for surviving a 100-year typhoon. Special design requirements for the mooring turret structural integration to the converted tanker are also discussed. Introduction The South China Sea hydrocarbon reserves are difficult to develop. The Liuhua 11-1 Field is reasonably typical, but has some unique features:The water depth is approximately 1,020 ft (310m); the location is about 120 miles (200 km) from shore.The metocean environment is such that major storms (typhoons) occur frequently.The site has solitons (internal waves) generated by tidal variations in the Bataan Strait.The crude in the reservoir is parafflnic, asphaltic, and contains both C02 and H2S in moderate quantities. The primary elements of a successful FPSO are:The shipThe mooring systemThe process facilities The solution to the FPSO design problem started with the selection of a vessel suitable for service as an FPSO in the design environment. Following this, the mooring system could be designed. The production facilities could be designed to accommodate both the processing requirements and the motions expected of the vessel. The ultimate requirement for an FPSO is to produce and store crude until it can be off-loaded to a shuttle tanker. In order to do this, it must have a reasonably stable platform and be capable of staying on-station during major storms.