Controls and quantitative characterization of stress sensitivity for coal seams

The stress sensitivity of coalbed methane reservoirs is strong, which has an important influence on the development of coalbed methane. Natural coal samples from different blocks were used to carry out stress sensitivity experiments, and two parameters, stress sensitivity coefficient and permeability damage coefficient were applied to evaluate the degree of stress sensitivity of coal samples. The stress sensitivity effects of coal rank, permeability and the gas pressure of a coal reservoir were studied. The results showed that when R_o is lower than 1.7%, the lower the coal rank is, the greater the degree of stress sensitivity is and the higher the extent of the permeability damage. When R_o is higher than 1.7%, the higher the coal rank is, the greater the degree of stress sensitivity is and the higher the permeability damage is. The empirical formula, put forward by this paper, between initial permeability and stress sensitivity coefficient can be used to predict the stress sensitivity coefficient of coal samples, which is convenient for pilot application. The lower the pressure of a gas reservoir is, the higher the permeability, which is advantageous for CBM development. However, lower gas pressure results in a slightly higher stress sensitivity coefficient and permeability damage coefficient, so avoiding stress sensitivity is important.