Abstract:

Reservoiring property bears close relation to metamorphic grade. According to the metamorphic grade, the Carboniferous and Permian Systems in North China could be divided into three kinds. In lower metamorphic coal beds, micropores developed well, but middle to big pores and fractures are not so well: though permeability and desorption are high enough, sorption capacity and methane content are both low. This kind of coal formations are not favourable for the diffusion and migration of coal-bed gas. High metamorphic coal suffered high pressure and high temperatiure, contains rich micropores, less fractures and less big to mid size pores. This kind of coal is not good in reservoiring property even if its sorption capacity and methane content are high. Mid metamorphic grade coal contains large amounts of internal fractures, big and mid pores developed well due to proper temperature and pressure. Most of the gas could be sorbed and preserved after generation, and the gas could be degraded, desorbed and migrated easily. This kind of coal is most favourable for coal-bed gas exploration. So it is proposed that the coal-bearing areas of the outer and inner flanks, the arc inside Taiyuan-Changzhi-Zhengzhou high metamorphic zone and the esat foot of Taihang Mountains should be taken as target areas for coal-bed gas explortion.