Abstract:

The multi-coalbeds area in Bide-santang Basin was taken as the study object. Depending on the results of previous researchs and combined with the isothermal adsorption and desorption experiments of 13 coal samples from different secondary synclines and the date of two CBM testing wells, the character of adsorption and desorption in coal reservoir under different gas-bearing systems was analysed and the relativity between gas-bearing system and the character of adsorption desorption was discussed. The research shows that with the coal layer going down the changing rules of adsorption character couldn’t match neither the vertical mutability in unattached multiple superposed CBM system nor the vertical monotonicity in unified multiple CBM system. There is no direct relationship between the type of CBM-bearing system and coal adsorptive capacity. Desorption has a lag compared to adsorption, and the smaller the Langmuir pressure is, the more obvious the lag shows. In unified multiple CBM system, the vertical desorption character of the same coalbeds shows inconformity and so does it in unattached multiple CBM system. The type of gas-bearing system can’t control desorption character in multi-coalbeds area. Thus, under muti-coalbeds conditions, the factor that can really affect adsorption and desorption is the reservoir conditions and coal properties, not the CBM-bearing system types.

Key words: CBM, Bide-santang Basin, multi-coalbeds, CBM-bearing system, adsorption and desorption