Chinese offshore operator China National Offshore Oil Corp (CNOOC) announced on Monday the discovery of its first deep coalbed methane (CBM) field with proved geological reserves exceeding 110 billion cubic meters in northwest China's Shaanxi Province, China Media Group (CMG) reported.

The discovery of the Shenfu deep CBM field, located in Yulin City of Shaanxi Province, at the eastern edge of Ordos Basin, is important for national energy security. It will further facilitate the growth of China's reserves and production of unconventional oil and gas, said CNOOC.

CBM refers to natural gas which is stored within coal seams, and deposits discovered at depths exceeding 1,500 meters are referred to as deep CBM. China has abundant CBM resources, with those buried at depths within 2,000 meters exceeding 30 trillion cubic meters. The deep CBM accounts for about one-third of the total, according to CNOOC.

Compared with medium and shallow CBM, the accumulation mechanism and geological conditions of deep CBM are more complex. As the burial depth increases, the formation temperature, formation pressure and stress also increase significantly, making exploration and development more difficult and costly.

A view of the Shenfu deep CBM field in Yulin City, northwest China's Shaanxi Province. /CMG

The coal seam of the Shenfu deep CBM field is about 2,000 meters deep and the thickness of a single layer is between 6 meters and 23 meters, with average gas content per tonne of coal reaching 15 cubic meters. Currently, more than 100 exploratory wells have been dug in the area, with a maximum daily gas output of 26,000 cubic meters per well.

Shenfu is CNOOC's second major CBM discovery following the Linxing field, which has similar proven gas in-place volumes.

Xu Changgui, deputy chief exploration engineer of CNOOC, said the discovery of the deep CBM field demonstrates the broad prospect of exploration and development in the eastern edge of the Ordos Basin.

"The discovery provides important guidance for exploration in similar basins and facilitates the growth of our reserves and production of unconventional oil and gas."

A view of the Shenfu deep CBM field in Yulin City, northwest China's Shaanxi Province. /CMG

"The discovery lays a solid foundation for the company to build a large onshore gas production base, which will tap up to 1 trillion cubic meters of proven gas in-place," CNOOC CEO Zhou Xinhuai said.

The company will continue to step up their efforts to increase onshore unconventional gas exploration and development, and continue to achieve new breakthroughs to ensure the national energy security, Zhou added.