A reservoir simulation study was used to investigate the effects of desorption pressure, geological setting and coal rank on the variation in permeability under in-situ conditions during coalbed methane production, based on a study in the Hedong area, Ordos Basin, China. The simulations allowed history matching of gas and water production from 12 wells with the actual well conditions specified as the model pressure. Good agreement was achieved between the model yields and the actual production data, suggesting that the changing permeability interpreted from the simulation is a realistic representation of the in-situ reservoir properties.The reservoir simulation study found that the decreases in permeability with production exceeded the increase in permeability caused by matrix shrinkage for nearly all wells in the Hedong area. The magnitude of the decrease in permeability increases as the gap between initial pressure and desorption pressure increases. The decrease in permeability is slower in the zone closest to the fault. The reservoir simulation has demonstrated that coal rank influences significantly the change in permeability during coalbed methane production.
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