China has started to drill an 8,875-meter-deep well in southwestern Sichuan Province to explore an untapped underground oil and gas field, sources with Sinopec Corp. said on Saturday.

With an estimated investment of 300 million yuan (38.8 million U.S. dollars), the drilling of the well, named "Chuanke No.1 Well", started in Mianzhu City in western Sichuan on March 20 and is expected to take 676 days to finish.

"We have made a smooth start by drilling 100 meters in the first four working days," said Zhang Xiaopeng, deputy chief engineer of Sinopec's Southwest China oil and gas company.

Zhang said that by drilling the well, Chinese scientists hope to learn more about the distribution of oil and natural gas in "ultra-deep stratum", which geologists refer to as stratum deeper than 7,000 meters.

Last April, Sinopec announced the discovery of the 356-billion-cubic-meter Puguang Gas Field in northeastern Sichuan, the largest gas field ever found in China.

"However, China has made no breakthrough in exploring gas in the so-called ultra-deep stratum," said Zhang.

In July, 2006, China completed drilling of the "Tashen No. 1 well", which is 8,408 meters deep, in Tahe oilfield in northwest China's Tarim Basin and used to be Asia's deepest, but did not discover gas.

"The drilling rig we are using this time is the first China-made rig that can go as deep as 12,000 meters" Zhang said.