By Christopher McFadden
October 24, 2023

Huge 100 billion m3 deep coalbed methane found in China

China's state-owned China National Offshore Oil Corporation has
 announced the discovery of an enormous deep coalbed methane reserve.

Image of the Shenfu deep CBM field in Yulin City, northwest China's Shaanxi Province.
 

State-owned China National Offshore Oil Corporation (CNOOC) has announced the discovery of its first deep coalbed methane (CBM) field. Located at around 4,921 feet (1,500 meters) in northwest China's Shaanxi Province, the coalbed has reported reserves of over 3,885 billion cubic feet (110 billion cubic meters). The Shnefu deep CBM field is located in Yulin City of Shaanxi Province, at the eastern edge of Ordos Basin.

Vital for energy security

The new coalbed will provide essential energy security for China and enable the country to boost production of unconventional oil and gas resources, explains CNOOC. CBM called coal seam gas (CSG), is natural gas found within coal seams. China is home to vast CBM resources, China Global Television Network (CGTN) reports, with 30 trillion cubic meters of gas buried at depths of up to 6,562 feet (2,000 meters). According to CNOOC, deep CBM accounts for approximately one-third of the total CBM resources in China.

Coalbed methane is a unique type of gas found in coal deposits. Unlike conventional gas reservoirs, the methane in coalbeds is stored through adsorption. The methane is almost in a liquid form, coating the inside pores in the coal, called the matrix. The cleats, the open fractures in the coal, may contain free gas or be filled with water.

Coalbed methane is a type of natural gas that differs from conventional natural gas in that it contains a few heavier hydrocarbons like propane or butane and no natural gas condensate. It typically has a few percent of carbon dioxide. Coalbed methane is generally formed due to the thermal maturation of kerogen and organic matter. However, in coal seams that experience regular groundwater recharge, methane is produced by microbial communities that live in situ.

However, exploring and developing deep coalbed methane (CBM) is more complex than medium and shallow CBM. Increased burial depth significantly increases formation temperature, formation pressure, and stress. These factors complicate the accumulation mechanism and geological conditions of deep CBM, making exploration and development more challenging and expensive.

The thickness of a single layer of the coal seam within the Shenfu deep CBM field varies between 20 feet (6 meters) to 76 feet (23 meters), and the average gas content per tonne of coal is approximately 530 cubic feet (15 cubic meters). Over 100 exploratory wells have been dug in the area, with the maximum daily gas output of 918,181 cubic feet (26,000 cubic meters) per well.

Shenfu is the second significant coalbed methane (CBM) discovery by CNOOC, following the Linxing field, which has similar volumes of proven gas in place. Xu Changgui, deputy chief exploration engineer of CNOOC, stated that the deep CBM field discovery showcases the vast potential for exploration and development on 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," he said.

One trillion m³

"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. Zhou stated that the company will continue to increase its efforts in onshore unconventional gas exploration and development and achieve breakthroughs to ensure national energy security.