China's largest offshore gas field in South China Sea fully operational

China National Offshore Oil Corp (CNOOC) announced that its Deep Sea No.1 Phase II project in the South China Sea has entered full operation, marking the completion of the country's largest offshore gas field, the CNOOC told the Global Times on Wednesday.

The Deep Sea No.1 gas field was developed in two phases. Phase I began production in June 2021. The field holds proven geological natural gas reserves of more than 150 billion cubic meters (bcm), and the field operates at a maximum depth exceeding 1,500 meters and includes wells that go beyond 5,000 meters in depth. 

It is China's deepest independently developed offshore gas field, featuring the highest formation temperature and pressure and the most complex geological conditions, according to a statement from the company. 

Phase II development was conducted under extreme geological conditions. The formation temperature reached up to 138 C and pressure exceeded 69 MPa — nearly 1,000 times the pressure of a household pressure cooker. The construction of the offshore wells and subsea production systems encountered major technological challenges.

According to Liu Kang, project manager of Deep Sea No.1 Phase II, the project used an industry-first model integrating a subsea production system, a shallow-water jacket platform, and a deepwater semi-submersible platform with remote operation capabilities. 

The system includes 12 subsea gas wells spread across three zones, one new jacket platform, one subsea production system, five undersea pipelines, and five deepwater umbilical cables. Together, they form a massive offshore production cluster spanning more than 170 kilometers in distance and more than 1,500 meters in water depth. 

The gas field has reached its designed peak production capacity, with annual output expected to exceed 4.5 bcm. The deep-sea gas is transported to onshore terminals in the Hong Kong Special Administrative Region, Sanya in Hainan Province, and Zhuhai in Guangdong Province, supplying the Guangdong-Hong Kong-Macao Greater Bay Area and Hainan, and feeding into the national natural gas pipeline network, the statement said.

Liu added that the facilities and technological system established through the two-phase Deep Sea drilling project will support future development of other complex deepwater reserves, such as Baodao 21-1 in the waters of Hainan, further strengthening the role of offshore gas in securing China's energy supply.