The phase II project of China's first independently-developed ultra-deepwater gas field Shenhai Yihao, or Deep Sea No. 1, became operational on Friday in waters southeast of Hainan, China's southernmost island province.

The operation of this project marks that China's capacity to develop oil and gas resources under complex conditions ranks among the top in the world, said the China National Offshore Oil Corporation (CNOOC), its operator, on Friday.

The phase II project, with a proven reserve of over 50 billion cubic meters of natural gas, has a peak annual natural gas output of more than 1.5 billion cubic meters.

The project includes 12 deepwater gas wells, a comprehensive processing platform weighing over 14,000 tonnes and five submarine pipelines with a total length of about 250 km, among other facilities.

Upon full operation of the project, the peak annual natural gas output of Deep Sea No. 1 is expected to increase from 3 billion cubic meters to 4.5 billion cubic meters, becoming an important source of gas supply and helping to ensure China's energy security, according to the CNOOC.

Jiang Ping, general manager of the CNOOC's Hainan branch, said that the development and construction of the phase II project had lasted for nine years. During this process, its builders faced various challenges, such as high temperatures and high pressure, and managed to achieve several key technological breakthroughs.

Deep Sea No. 1, located 150 km from the city of Sanya in south China's island province of Hainan, is