Research on pre-pumping gas control technology for large-diameter borehole

Abstract

The large quarry face with a strike length of 3 300 m in Sijiazhuang Mine features high gas reserve, large gas outflow and its upper corner is easy to exceed the limit.This study adopts the gas management technology of extracting the gas from the coal seam by drilling large-diameter downhole holes.We established a numerical model of fluid-solid coupling by considering the superposition effect of drill holes to analyze the evolution of gas pressure, effective extraction radius, and the effect of gas extraction when the diameter of drill holes is 113 mm and 400 mm respectively.The results show that ①after implementing pre-extraction technology in the large diameter drill hole, the effective extraction radius of the drill hole increased by 21.12 %; ②When introducing the coefficient k=pm/pc as a judgment index of the superposition effect, taking the effective extraction radius of a single 113 mm diameter drill hole as a reference, the effective radius of a 113 mm diameter drill hole is improved by 3.7 times compared with that of a single hole when using a common diameter drill hole for multi-hole extraction; ③The concentration of the gas extracted from the drill hole increased by 2 times, and the pure amount of extraction increased by 5 times, which provides technical and theoretical references for the gas management and safe production of the working face of large mining fields.

Keywords

• gas control
• oversized diameter drilling
• numerical simulation
• fluid-solid coupling
• superimp-osed effect