Numerical simulation of gas emission during borehole drilling

In order to analyze gas emission during borehole drilling, a model of fluid-solid coupling dual-hole media was established, and the effects of gas pressure, borehole diameter, matrix desorption time and Klinkenberg factor on gas emission during borehole drilling were simulated and analyzed. The results show that the exposure time, pressure drop and gas seepage rate are different at different positions of hole wall. The gas flow shows a growing trend and the growth rate keeps slowing down, and using a single-hole model will seriously overestimate gas flow. The gas pressure is the key factor affecting gas emission in drilling; the increase of hole diameter promotes the increase of gas flow and emission; the increase of matrix gas desorption time reduces the gas replenishment to the fracture; Klinkenberg factor can significantly promote the increase of permeability, thereby increasing the seepage speed and increasing the amount of gas emission, but there is a limit value of gas emission.