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Feature Article

FSOU Mooring, Riser System Upgrade

By Shaik Baba

The buoy turret mooring system for
the Lufeng NanHai Sheng Kai.
InterMoor (Houston, Texas) and Offshore Installation Services Ltd. (Norwich, England), or OIS, worked together on a floating storage and offloading unit (FSOU) mooring and riser system upgrade at Lufeng field for Chinese installation contractor Offshore Oil Engineering Co. Ltd. (COOEC) of Tianjin, China. The Lufeng field Nanhai Sheng Kai (NHSK) FSOU mooring and relocation project was undertaken in the South China Sea, 370 kilometers offshore Hong Kong, China, over six months from March to August 2012.

The NHSK FSOU was moored with a single-point mooring in a water depth of 142 meters using a disconnectable buoy turret-mooring system by SOFEC Inc. (Houston, Texas). The existing mooring system at well LF 13-1 had entered service in 1992 and had been operational far beyond its design life of 12 years. The system was showing signs of deterioration and corrosion.

The field operator, CNOOC Ltd. (Hong Kong, China), planned to extend the service life of the FSOU for another 15 years by refurbishing it, and upgrading and relocating its mooring system to well LF 13-2. This would enable production from Lufeng field to continue in a safe and reliable manner, and would also support future field development.

InterMoor was responsible for all of the mooring-related activities on the project, including providing a specialist engineering team. OIS took responsibility for project management, including offshore management of the Maersk Attender and the HYSY708, and all riser-related activity.

The InterMoor—OIS project team was assisted by 2H Offshore (Houston), which provided riser-installation engineering, and Aquatic Engineering & Construction Ltd. (Aberdeen, Scotland), which supplied offshore personnel and equipment for deploying the flexible riser.

As part of the project, procedures were developed that enabled operations to be performed simultaneously offshore, while working with divers, ROVs and the anchor-handling vessel in close proximity to the buoy turret mooring system.

Mooring Installation
The overall work scope for the project involved temporary replacement of the buoy turret mooring system at well LF 13-1 to accommodate the Nanhai Kai Tuo (NHKT) FSOU and enable continuing production from the field throughout the project; project management, engineering, procurement and installation of a new buoy turret mooring system for the upgraded NHSK FSOU at well LF 13-2; and installation of a new 8-inch static flow line (1,687 meters) from Technip (Paris, France) and an 8-inch dynamic riser (412 meters), also from Technip, between the buoy turret mooring system and the LF 13-2 wellhead platform.

The interim buoy turret mooring system replacement involved disconnecting, by ROV—Oceaneering International Inc.'s (Houston) Magnum Plus dual-manipulator 170-horsepower work-class ROV and Millennium Plus dual-manipulator 220-horsepower heavy work-class ROV—the buoy from the riser and placing it on the seafloor; disconnecting the existing mooring lines and removing the buoy; replacing the top chains and riser wires for the mooring lines using diver assistance in hookup; and reinstalling the riser system into the buoy for connection to the NHKT FSOU, using an adaptor end fitting. To continue this article please click here.

Shaik Baba is a senior naval architect at InterMoor who has a bachelor's in engineering with a specialization in naval architecture and a master's in technology with a specialization in information technology from Andhra University in India. He has 14 years of experience in marine and offshore engineering, including his work at Det Norske Veritas's (DNV) Jurong shipyard in Singapore.

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