Coal rock gas development will become the main force for increasing natural gas production in China (Part 1)

Against the backdrop of the "dual carbon" goal and accelerated energy transition, increasing natural gas production has become a core concern for the industry's development. According to statistics, China's natural gas production has increased from 30 billion cubic meters in 2000 to 240 billion cubic meters in 2024, ranking fourth in the world. At the same time, the development of unconventional gases is still on the road to breaking through cognitive barriers. Among them, coal rock gas is expected to become a "new blue ocean" of natural gas to fill the bottleneck of CBM development.

"The discovery of coal rock gas is actually an 'unexpected joy' after the bottleneck of CBM development. Essentially, it comes from coal seams and is stored in coal seams, but the core difference is that the geological characteristics of resources are different." Jia Chengzao, an expert in petroleum geology and an academician of the CAS Member, said that China's natural gas production is growing rapidly, basically relying on conventional gas, tight gas and shale gas, and CBM contributes very little. In the deep coal seams that have not been damaged by tectonic uplift, a large amount of free gas is retained, which can be extracted without drainage and pressure reduction. The single well production and reserve abundance are much higher than those in the shallow layers.

We ultimately named this resource as coal rock gas, and its discovery fills the resource gap outside of coalbed methane. In China's coal bearing strata of the Carboniferous Permian and Jurassic periods alone, the predetermined resource amount may reach 30 trillion cubic meters, which can be regarded as a new hope in the field of natural gas, "said Jia Chengzao.

Since the 1990s, Chinese petroleum exploration technology workers have been tackling the development technology of coalbed methane. At that time, horizontal well technology was introduced from abroad and extracted in coal mining concentrated areas such as Shanxi. The gas adsorbed in the nano pores of the coal matrix was released by pumping and lowering the pressure, "recalled a technician from China Petroleum Exploration and Development Research Institute who participated in coalbed methane exploration at that time. However, due to the low amount of free gas in shallow coal seams, which mainly relies on adsorbed gas desorption, the daily production of single wells is often very low, far lower than conventional gas, and the economic benefits are poor. Coalbed methane has never been able to become the main force of natural gas growth.

In recent years, coal and rock gas have gradually entered the public eye. From the perspective of petroleum and natural gas geology, the fundamental difference between coal rock gas and coalbed methane lies in the differences in geological evolution processes, with significant differences in reservoir states and development characteristics. Geological profiles can clearly distinguish between them: a continuously distributed coal seam has a clear depth boundary, with coalbed methane above the boundary and coalbed methane below it.

Named 'coal rock gas', it has both scientific basis and practical considerations. Jia Chengzao said that coal rock gas is a new type of gas reservoir with coal rock as the source rock and reservoir, belonging to the' self generation and self storage 'category. Although similar to shale gas, coal rock is mainly composed of carbonaceous materials, and the characteristics of the dual medium reservoir with developed cleavage are completely different from sandstone and carbonate rocks, making it an independent gas reservoir type.