Study on Pressure Sensitive Effect of Permeability of Raw Coal with Containing Gas and Low Permeability

Abstract

Based on the low permeability raw coal samples of coal seams of Daichiba coal mine of Guangwang group, we study the change of permeability under different stress states by a self-developed three-axis penetration device. It is proved by experiments that the permeability of coal sample increases rapidly along with the growing of the pressure at the procedure of loading at lower actual stress levels whose rules of changes is the function of negative exponent. In the process of unloading, rate of permeability increase slowly with the reduction of effective stress. It will greatly improved when the effective stress drops to a certain level, and this conformed to power function law. As the influence of coal seam gas permeability solid coupling factors is very complex, the normalized treatment for the factors has done by defining pressure-sensitive effect coefficient of coal samples permeability. Based on the results of the test to establish the relationship between pressure sensitive effect index and effective stress, this relationship reflects the trend of the coal sample permeability changes in the effective stress. And derive a functional relationship based on the coal sample of the pressure-sensitive effect index of permeability and effective stress.