Study on influence of hydraulic flushed borehole on evolution law ofcoal reservoir permeability

In order to study the permeability evolution law of coal surrounded of hydraulic flushed borehole shape and hydraulic flushed borehole in the coal reservoir, according to the Bergmark-Roos Equation, a shape feature equation of the hydraulic flushed borehole was established and the borehole shape was represented with the Matlab simulation. Based on the fluid-solid coupling and stable creep theory, the numerical simulation method was applied to prove through an investigation the permeability evolution law of the coal during the hydraulic flushing period and after the hydraulic flushing of the borehole. The study results showed that the hydraulic flushed borehole was in an ellipsoid. During the hydraulic flushing period, with the coal output increased, the influenced radius would increase.With the time passed, the coal permeability within the influenced radius would increase and then in stable. After the hydraulic flushing of the borehole, the cracking deformation degree of the coal borehole would increase with the time passed and the permeability would decrease.The results of the established fluid-solid coupling equation and the numerical simulation could be basically fitted to the site practices.