Non-Darcy Flow MTS Permeability Experiment of Coal Samples of a Gas-rich Coal Mine

Coal samples were collected from a Gas-rich coal mine and standard samples are made from them to obtain the seepage properties of non-Darcy flow of such coal rocks. Tests of coal samples under complete stress-strain process and full-process displacement control were conducted by using the MTS-02 rock mechanics testing system and the numerically controlled transient permeability method. Under 4 MPa confining pressure and 15 MPa/m pore pressure difference,the non-Darcy flow permeability,the non-Darcy flow factor β,the acceleration coefficient and the seepage stability index of the coal samples under different strains during failure process were worked out and the pressure gradient for seepage instability to take place was given. It shows that the samples have better brittleness and have better relaxation property in the process of maintained stress. During the complete stress-strain process,the permeability is lower and does not change significantly before peak stress,but after peak stress,the permeability increased range is very great. The non-Darcy flow factor β almost has negative values during the strain-growing process,and that the negative values of seepage stability index occur only after the peak stress. The seepage instability disasters show as gas emission suddenly from coal-rock crack or even gas blowout take place. 5figs.,1tab.,8refs.