Weizhou SPM: A Process And Storage Tanker Mooring System For China

ABSTRACT Located in the South China Sea, the WEIZHOU SINGLE POINT MOORING (SPM) is a fixed structure standing in 37.5 m water depth in an area where the risk of typhoon is significant. Connected to the near-by platform by sea-line, it is designed to permanently moor, by hawser, a 174,000 DWT tanker, where most of the oil treatment and production operations will be performed. The SPM is equipped to handle a two-phase crude production stream from the wells plus injection water. Provision is made in the design for the equipment necessary to accommodate gas-lift operations. The High Pressure Multi-Path (HPMP) Swivel, one of its most important equipment, is designed with three fluid paths to accommodate crude production at 6 MPa (900 PSI), injection water at 14.5 MPa (2,100 PSI) and gas at 20.0 MPa (2,900 PSI). The paper gives a complete description of the SPM and its main equipment: the mooring table and the HPMP swivel. The means that allow the rapid disconnection of the tanker in case of typhoon are also described. INTRODUCTION The WEIZHOU field located in the BEIBU GULF in the South China Sea is operated by TOTAL-CHINE, on behalf of a consortium including for the Chinese party NAN HAl WEST OIL CORP., for the foreign party TOTAL CHINE, ELF AQUITAINE CHINE, LA.C.O., SEIBU OFFSHORE OIL DEVELOP. COMP. and STATOIL. Based on an expected production rate of 30 000 bbls/day in the first development phase, and on early production start-up consideration, TOTAL-CHINE selected a light field development scheme which stands on the use of an unmanned well head platform and on a Process and Storage Tanker (PST) moored nearby to an SPM (Single Point Mooring). Beyond its basic functions of mooring the PST and transferring fluids, the SPM incorporates production equipment such as pig traps, by-pass and shut-down valves to meet the requirements of safety. After a preliminary study during which other types of SPMs were assessed, a fixed structure was retained because of the advantages it offers in regards to the high pressure flexible hoses' configuration and production equipment installation. The design of the SPM started in early 1985 and its delivery is scheduled for the end of March 1986, i. e. 1ess than a year after contract award. Insta1lation is scheduled for April 1986. WEIZHOU OIL FIELD Site data As shown in Figure 1 the WEIZHOU field is located in the BEIBU GULF (GUANGDONG province) about 50 km offshore. The water depth at the 1ocati on of the SPM is 37.5 m and the one hundred year return conditions are as follows. These very severe conditions were the major concern when designing the system. Particularly:Such conditions led to replacing the rigid mooring arm usually used for permanent moorings by a mooring hawser that can be promptly disconnected when heavy storms or typhoons are expected.