Wenchang 9-2/9-3/10-3 gas fields are located offshore China in the South China Sea. Image courtesy of Offshore Oil Engineering.
The Offshore Oil 228 barge was used to inset the topsides in the subsea-rooted jacket. Image courtesy of Offshore Oil Engineering.
First gas from the project is expected to be achieved in 2019. Image courtesy of Neway Valve.

Wenchang 9-2/9-3/10-3 gas fields are located 146km from the east coast of Wenchang in the western part of the South China Sea.

The fields are owned and operated by China National Offshore Oil Corporation (CNOOC). The project is expected to produce first gas by 2019 and have a peak production capacity of 14,300 barrels of oil equivalent per day (boe/d).

Wenchang 9-2/9-3/10-3 gas fields discovery and appraisal

The Wenchang 10-3 and Wenchang 9-3 gas fields were discovered and appraised during 2005, along with CNOOC’s other discoveries Bozhong 3-2, Luda 27-2, Weizhou 11-1N, Weizhou 11-4N, Liuhua 19-5, Bozhong 19-4N and Huizhou 25-3.

The Wenchang 9-2 gas field was also successfully appraised during the same year.

Wenchang 9-2/9-3/10-3 gas fields development details

The Wenchang 9-2/9-3/10-3 gas fields will be developed using the Wenchang 9-2/9-3 central platform, which includes a subsea-rooted jacket, leg mating unit (LMU), and deck supporting unit (DSU) and topsides weighing 13,000t.

The topsides are equivalent to the size of eight football grounds and have a height of 15 floors. They are equipped with a gas turbine generator (GTG), which was pre-commissioned on liquefied natural gas (LNG) to increase efficiency and reduce greenhouse gas emissions.

The topsides were installed on the subsea-rooted jacket by the Offshore Oil 228 barge using the floatover method, which is a widely adopted low-cost installation technology providing advantages such as fast installation and improved lifting.

Subsea infrastructure details

A 23km-long umbilical cable, made of Sandvik SAF steel tube with an outside diameter of 1.28cm, was used to link the central equipment platform. The umbilical cable was independently developed, designed and manufactured domestically. It was installed in water depths ranging from 110m to140m.

The umbilical was installed by the MW603-1 vessel, which is equipped with a DP-2 system and can carry up to 3,500t submarine cable for cable-laying, transportation, operations and maintenance.

Gas transportation details

The gas produced by the fields will be connected to the Yacheng pipeline by means of submarine pipelines and transported onshore to the Hainan, Guangdong, Hong Kong and other regions.

The Yacheng pipeline is a 780km-long, 28in diameter pipeline, which was developed as part of the Yacheng 13-1 gas field development.

Installation equipment details

The Offshore Oil 228 barge used to install the topsides of the central platform is an 180,000t barge developed in 2012 for jacket launch and float-and-drag module installation. The barge was able to withstand Level 4 offshore wind power and remained stable during the installation.

Contractors involved

Fluor carried out pre-commissioning services along with fabrication design, fabrication, construction and loadout of the Wenchang 9-2/9-3 central platform.

Orient Cable supplied the umbilical cable, while COOEC Subsea Technology performed cable installation.

CNOOC Engineering, a subsidiary of Offshore Oil Engineering, carried out the installation of the topsides for the Wenchang 9-2/9-3 central platform.

Neway Valve supplied subsea gate valves and subsea ball valves for the project. Other subsidiaries of CNOOC involved in the project are CNOOC Research Institute and CNOOC Zhanjiang Branch.

CNOOC’s operations in South China Sea

The Wenchang 9-2/9-3/10-3 gas fields lie in the Western South China Sea, which is a vital region for CNOOC’s natural gas production.

The reserves and daily production volume of the area stand at 844.1 million barrels of oil-equivalent and 142,870boe/d, which accounts for approximately 17.4% of the company’s total reserves and 11.1% of its daily production.

The company discovered six fields in the area in 2018, including Weizhou 11-2 East, Weizhou 11-12, Wenchang 9-3 South, Wenchang 19-9, Wushi 22-8 and Wushi 23-5/23-5 South.