This file photo shows the drilling site of the Jiyang shale oil national demonstration zone in east China's Shandong Province. [Photo/Xinhua]

The China Petrochemical Corporation (Sinopec Group), the country's largest oil refiner, has announced the discovery of more than 140 million tonnes of proven shale oil reserve in east China's Shandong Province.

This is the first shale oilfield with proven reserves exceeding 100 million tonnes to be certified by the Ministry of Natural Resources, and a major breakthrough in oil and gas exploration in the Jiyang shale oil national demonstration zone.

To date, the estimated shale oil resources have reached 10.5 billion tonnes in the demonstration zone, owned by the Shengli Oilfield in Shandong, with cumulative oil output surpassing 1 million tonnes.

"The estimated shale oil reserves of Shengli Oilfield are equivalent to the conventional oil and gas resources discovered in Shengli Oilfield over the past over 60 years," said Sun Yongzhuang, assistant president of Sinopec and executive director of Shengli Petroleum Administrative Bureau Co., Ltd.

The Shengli Oilfield was discovered in 1961, and its development began in 1964.

Shale oil mainly refers to liquid hydrocarbons that are trapped in formations of shale rock that can be extracted for refining. It is often found in organic-rich shale and thin interlayers of carbonate rocks, sandstones and siltstones.

China has established three national-level shale oil demonstration zones in Xinjiang Uygur Autonomous Region, Heilongjiang Province and Shandong Province, respectively.