Experimental research on stress sensitivity of coal reservoir and its influencing factors

Abstract：Adopted samples from the high-rank coal reservoirs in Southeast margin of Ordos Basin,through the stress sensitivity experiment of coal samples,stress sensitivity of coal reservoirs and the effects of effective confining pressure,fractures inside the coal and water condition on stress sensitivity were analyzed.The results show that,the permeability decreases according to negative exponential function with the increase of effective stress.When effective stress changes from 2.5 MPa to 10 MPa,dimensionless permeability of the coal samples is 0.10～0.28,and the average value is less than 0.15;the damage rates of permeability are 71.92%～90.14%,and the average value is 84.59%.When effective stress is less than 5 MPa,the coal reservoir permeability decreases rapidly with the increase of the effective stress,the stress sensitivity is the highest;when effective stress is between 5 MPa and 10 MPa,the stress sensitivity is medium;when effective stress bigger than 10 MPa,the decline of the permeability slow down,and the stress sensitivity is weak.The initial permeability of coal samples with fractures inside is higher,and the stress sensitivity is relatively small;the irreversible plastic deformation generated larger in the lifting-pressure process results in relatively high irreversible damage rates after the pressure decreas.The permeability of wet coal samples reduces rapidly with the increase of effective pressure,with the increase of moisture content,the stress sensitivity is more obvious.