Experimental study on stress sensitivity of coal and rock fracture permeability ineastern Yunnan and western Guizhou

The permeability of coal and rock is generally low in eastern Yunnan and western Guizhou, but the in-situ stress is high. The change of effective stress of coal seam will significantly affect permeability of reservoir. In order to study the stress sensitivity mechanism of coal fracture permeability, the stress sensitivity experiment was carried out for coal samples collected from the region of eastern Yunnan and western Guizhou, and the structure characteristics of coal samples were analyzed by scanning electron microscopy (SEM). The test results show that the fracture permeability of coal and rock and the effective stress show a negative exponential relationship. When the effective stress is less than 10 MPa, the fracture permeability of the coal seam decreases sharply with the increase of the effective stress, and the permeability damage mainly occurs at this stage; when the effective stress is greater than 10 MPa, the fracture becomes more and more difficult to be compressed, the downward trend of fracture permeability slows down. Both natural and artificial fractures of coal rock have strong stress sensitivity. Microscopic images show that the surface roughness of natural fractures is smaller, and the filler can be used to support the fracture closure. The stress sensitivity of artificial fracture is stronger than that of natural fractures. In the process of CBM development, it is necessary to control the production pressure difference reasonably to reduce the damage of stress to permeability, and ensure the efficient production of CBM wells.