Coupling Relationship and Control Mechanism Between Coal Permeability and Effective Stress

Taking the 3^# coal in Sihe Mine in the southern of Qinshui Basin as the research object. Through the effective stress sensitivity test of coal sample, the correlation between the permeability of coal rock and stress was analyzed, and the coupling model of coal reservoir permeability and stress is verified. The results show that the permeability of coal has obvious correlation with the effective stress, and shows negative exponential decay with the increase of effective stress. Fracture plays an important role for the sensitivity of coal permeability to effective stress, and is basically closed when the effective stress is greater than 9.45 MPa, which makes the permeability less sensitive to stress. The change of stress of coal rock reservoir will produce plastic (destructive) deformation of coal rock and its pore structure, resulting in irreversible decrease of coal reservoir permeability and the degree of irreversibility is more than 50%. The plastic deformation of the fracture occurs mainly in the stress sensitive area and the transition zone, and in the transition from the stress sensitive area to the transition zone, there will be a “trough” in the attenuated non-dimensional permeability value; in the transition from the stress transition zone to the insensitive zone, the attenuated non-dimensional permeability value will have a “wave peak”.