China National Offshore Oil Corporation(CNOOC)Limited,the listed unit of China's largest producer of offshore crude oil and natural gas,said that China's first deep-water oilfield secondary development project—the Liuhua 11-1/4-1 Oilfield Secondary Development Project—has produced crude oil exceeding 700,000 tons after one year's operation,Science and Technology Daily reported on Saturday,citing the information from the company.

This development has surpassed expectations,showing that CNOOC has successfully overcome the world-class challenge of developing offshore reef limestone oilfields,the company said.

Reef limestone oilfields are widely recognized as one of the most difficult types of reservoirs to develop.Beneath such reservoirs,there often exists a massive"water cushion."Once extraction begins,bottom water rapidly advances through the path of least resistance—porous cavities—leading to uncontrolled channeling and quick flooding of oil wells,leaving significant amounts of crude oil unrecoverable.

After a decade of concentrated efforts,CNOOC has developed a series of technologies for controlling water and stabilizing production in offshore reef limestone reservoirs,significantly enhancing the recoverable reserves and recovery rate of the Liuhua 11-1 oilfield,the CNOONC said.

The Liuhua 11-1 oilfield is China's first deep-water oilfield,becoming the country's largest offshore reef limestone oilfield in terms of proven geological reserves to date.

Since its initial production in 1996,the oilfield has produced over 20 million tons of crude oil.However,the recovery factor remains at only 12.84 percent,with approximately 140 million tons of crude oil still trapped deep within the submarine formation.