Metamorphic degree of coal dependence of content and genesis of coal-bed methane in China

Aiming to investigate the coal metamorphic degree dependences of both the distribution characteristics of the content of CBM and the output characteristics of CBM, the thermal simulation experiments were adopted in this study. The results confirm that the content of CBM shows a unimodal relationship with the elevated coal metamorphic degree. The CBM in high-rank coal-bed mainly falls into the category of thermogenic CBM. The thermogenic CBM is generated after the thermal stability of coal metamorphism. The output characteristic of thermogenic CBM is the dominant factor determining the relationship between content of CBM and coal metamorphism degree. Both the amount of thermogenic CBM and the content of CBM increase with the coal metamorphism degree with R-o max <= 3.5%; however, the opposite trend is found for R-o max >= 3.5%.