Analysis on coalbed methane drainage data and dynamic prediction of reservior permeability in Fanzhuang Block

In order to calculate the changes of permeability of coalbed reservior more accurately,three mathematical models were established by considering the effect of stress sensitive,matrix shrinkage and gas slippage on the permeability of coal based on the controlling mechanism of coal reservoir permeability and material balance eq uation. A theoretical method for permeability of coalbed with drainage data was finally developed. Four wells from Fanzhuang Block in southern Qinshui Basin were then e mployed for a case study,in which synthesized results were obtained about variation of permeability under different geological effect and the main controlling factors of coal reservoir permeability during different production stage were analysed. The results showed that the pressure drops was positively correlated with the rate of permeability C hange made by effective stress or matrix shrinkage; the effects of gas slippage could not be ignored under low reservoir pressure and low permeability condition; in early st age,CBM permeability was controlled by three effects synthetically and the slippage effects was dominant under reservoir pressure of lower than 2 MPa.