Study on Permeability Rate Variation Features of Mine Coal Bed Methane Reservoir Duing Gas Drainage Process of Coal Bed Methane Well

With the establishment of the mathematical model between the variation rate of permeability rate and volume strain of coal reservoir.The variation of the volume strain and permeability rate in the seam reservoir during the coal bed methane development process was investigated.The results showed that the volume strai n of the seam reservoir during the coal bed methane development process could be divided into two stages .At the initial stage, the volume would be shrunk and the vol ume strain would be negative .With the effective stress varied, the volume strain would be steadily be positive and would be continuously increased .But the permeability rate would have an asymmetric U type variation with firstly reduction and then increasing and finally would be increased by 1.5 times.