China National Petroleum Corporation announced on Sunday the discovery of a shale oil field with geological reserves of 1 billion tonnes in northwest China's Ordos Basin, making it the largest in the country.

The leading energy company said the accumulated proven geological reserves of its Changqing Oilfield reached 1.052 billion tonnes thanks to breakthroughs in core technologies like horizontal drilling. 

Proven reserves – resources that can be recovered with existing technology after detection – of 359 million tonnes were found in 2019, 143 million tonnes in 2020 and another 550 million tonnes in the first five months of this year. 

It is estimated that by the end of the 14th Five-Year Plan period (2021-25), the shale oil capacity in the Changqing Oilfield will exceed 5 million tonnes with output exceeding 3 million tonnes.

Shale oil is a type of unconventional oil found in sedimentary rock that requires fractional extraction. The heavier, waxy oil is more difficult and costly to recover than traditional crude. 

Top global holders of technically recoverable shale oil resources include the United States, Russia and China.

Read more: China discovers 900m-tonne oil and gas field in Xinjiang