Offshore oil and gas production company CNOOC Limited announced on Tuesday that it has drilled a natural gas well in the ultra-deepwater Liwan 4-1 structure in the Pearl River Mouth Basin, the first major exploration breakthrough in ultra-deepwater carbonate rocks offshore of China.

The well, located in Baiyun Sag, is the largest hydrocarbon-rich sag in the Pearl River Mouth Basin, about 300 kilometers southeast of Shenzhen with a water depth of nearly 1,640 meters, and was tested to produce 430,000 cubic meters of absolute open flow natural gas per day, the company said.

The well was drilled to a vertical depth of nearly 3,000 meters, completed at a depth of nearly 4,400 meters, and encountered gas pay zone of approximately 650 meters in the horizontal section.

"While exploration in China's ultra-deepwater areas mainly focused on clastic rocks previously, the success of this well has, for the first time, revealed the enormous potential of carbonate rocks in China's ultra-deep waters, marking significant breakthroughs in both exploration understanding and operational techniques," said Xu Changgui, CNOOC's chief geologist.

"In addition, this discovery is close to the existing production facilities of Liwan 3-1 gas field, which could be utilized to develop the new discovery, thereby enabling economic and efficient development of natural gas resources in the deep waters of the Pearl River Mouth Basin."