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Abstract Reasonable bottom-hole pressure is closely related to the mechanical properties of coal rock and the stress distribution around the well，and there is an interdependent relationship between the stress distribution around the well and the pass-through cracks which can increase the absolute permeability. Firstly，based on the experimental results of coal rock in Hancheng，the varying law of the absolute permeability with the different stress states around the well is analyzed in this paper. And then，according to the elastic-plastic theory and through the elastic-plastic analysis to the rock around the well of fissures，the mathematical models on the relationships between the stress around the well and the bottom hole pressure are established. Finally，the reasonable range of the bottom hole pressure is obtained to maintain or improve the absolute permeability，and to be applied in the practical analysis of coal bed methane(CBM) engineering in Hancheng. Thus，under a given condition of CBM engineering，it can be found that the absolute permeability will do higher growing and the methane production will be further improved，if the bottom-hole pressure can be controlled reasonably.
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Received: 10 December 2010
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2011, Vol. 30 
