Coalbed gas is a kind of unconventional and coal formed gas that is mainly composed of methane.The gas is preserved in 3-D reservoir networks in the coalbeds.Its reserve is much greater than that of free gas and dissolved gas preserved in pores and fractures.It is this property that decides the gas migrating and dispersing weakly and preserving easily in large areas.In geological evolution

the existence of stable post structures

complete hydrodynamic system and well sealed coalbeds are necessary for the formation of coalbed gas reservoirs.China's five tectonic regions are situated respectively in stable regions(represented by continent blocks)and active regions(represented by continental margins).Among them

Tarim-North China and South China regions are stable ones

the coal-forming stages of the regions were favourable for the formation and preservation of coalbed basin.