Abstract

The FPS, " NANHAI TIAO ZHAN", is a major component of the Liuhua 11–1 project. It is a converted from a Sedco 700 series mobile offshore drilling unit (MODU) into a floating production system. This FPS hull and mooring system are designed to maintain station in 100 years return typhoon environment.

The Semi-submersible FPS " Liuhua 11–1" registered ABS class. The latest request from the client was a comprehensive assessment for 15 years life-extension. According to the contract between the client and ABS, ABS surveyor should do multiple survey to this unit, including on-site inspection for the unit structure (welding and corrosion), steel plates thickness measuring, etc. In addition, ABS engineer should do strength re-assessment to the structure when received the submissions of Global Strength Analysis and Global Fatigue Analysis from the client, then make comments about structure reinforcement according to the re-assessment result. This paper is to list the related requirements from related ABS rules and guides, including ABS Guide for Building and Classing Floating Production Installations, ABS Rules for Building and Classing Mobile Offshore Drilling Units, ABS Guide for Fatigue Assessment of Offshore Structures, and other regulations, such as IMO Code for The Construction and Equipment of Mobile Offshore Drilling Units, etc., other industrial standards for reference during analysis.

Introduction

The Liuhua 11–1 oil field is the largest oil field in the South China Sea so far. It was originally developed by a consortium of Amoco, CNOOC and Kerr-McGee in 1995. The main components include a floating production system " NANHAI TIAO ZHAN", and a floating production, storage and offloading vessel " NANHAI SHENG LI" which is located about 3000 m northwest of the " NANHAI TIAO ZHAN" FPS.

The original Liuhua 11–1 project was the first deepwater development project in China with in more than 1000 ft water depth. Liuhua 11–1 project was one of the major deepwater developments adopting new technologies with unique features in early 1990's for the whole offshore industry. This oil field is still in production. A new oil field Liuhua 4–1, about 11km away from Liuhua 11–1, was planned to be processed by the Liuhua 11–1 FPS facilities via subsea tieback. In this regard, additional topsides capacities and life extension for the aged semi-submersible FPS " NANHAI TIAO ZHAN" were requested. Significant technical challenges were imposed to the project team for the life extension and dry docking upgrade of the FPS. The FPS upgrade project started in 2010, and riser and mooring offshore reconnection was completed in 2012. The upgraded Liuhua 11–1 FPS is now back to the oil field and in production again successfully.

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