China's first independently-developed ultra-deepwater gas field Shenhai-1 (Deep Sea No. 1) has completed the operation at the first development well of its second phase project with production capacity beyond expectations, operator China National Offshore Oil Corporation (CNOOC) said on Monday.

The testing showed that the well can produce more than 1 million cubic meters of natural gas and over 230 cubic meters of condensate daily, far beyond the design expectations, which confirms the effectiveness and reliability of the full set of self-developed deepwater oil and gas exploration technologies applied in practice, said the CNOOC.

Located in the southern waters of south China's Hainan Island, the second phase of the Shenhai-1 gas field adopts a construction mode integrating an underwater production system, shallow-water jacket processing platform and remotely controlled deepwater semi-submersible platform, and deploys 12 underwater gas wells in three areas.

The operation at the first development well was rather challenging.

It was completed at a water depth of almost 1,000 meters with a drilling depth of more than 5,000 meters. The horizontal distance between the end of the well structure and the wellhead was of more than 2,000 meters, and the inclination reached up to 91 degrees.

The total drilling length of the second phase will be 2.2 times that of the first phase, and the operation of the first well accounts for 80 percent of the total drilling work, according to Liu Shujie, chief engineer of the CNOOC Hainan subbranch.

After the completion of the second phase, the natural gas reserves of Shenhai-1 gas field will be enlarged from 100 billion cubic meters to 150 billion cubic meters. The peak annual production will increase from 3 billion cubic meters to 4.5 billion cubic meters, equivalent to 90 percent of natural gas consumption of Hainan Island in 2021, which will provide a strong guarantee of clean energy for south China regions.