Determination and Application of Reasonable Levels for Highly Directional Long Boreholes in Deep Outburst Coal Seams

Abstract

In order to solve the problem that the gas in the upper corner is easy to exceed the limit in the mining process of the deep outburst coal seam. Based on the theory of “O-ring” and the distribution of stratigraphy in the field, the development law of mining fissures in the overlying rock layer during the workface retrieval was studied by combining theoretical calculation and FLAC3D numerical modeling. The research results show that the range of fissure development zone in 2913 working face is 14.2 to 33 m from the coal seam roof, and the high drilling arrangement can be in the stable rock layer of the roof. For siltstone-fine sandstone interaction stratum, measures such as opening branches to adjust the layer and lowering the casing to protect the hole wall can be taken to ensure the stability of the borehole and the smooth flow of gas extraction channels. Field application shows that the high directional long borehole has the advantages of long extension distance and wide coverage, the average value of extraction mix is 34.3 m3/min, and the average value of extraction pure is 0.4 mm3/min, which helps to prevent the gas overlimit in the upper corner during the workface recovery. The high directional long borehole has obvious economic and safety benefits over the traditional high hole and has important promotion value in coal mine gas management.

Study and Application of High-Level Directional Extraction Borehole Based on Mining Fracture Evolution Law of Overburden Strata

“…Complex distribution, properties and mechanical parameters of roof strata greatly affect the mining fracture evolution law of overburden strata. At present, different multifunctional testing methods and devices have been invented and applied to collect the evolution law of the fissure surface, deformation, displacement, and stress in a timely manner to guide the design and drilling of high-level directional extraction boreholes [28][29][30]. However, a single testing method cannot reflect the detailed changes in the roof strata, and the mining fracture evolution law and deep roof strata cannot be directly observed.…”

Study on the Coupling Effect of Stress Field and Gas Field in Surrounding Rock of Stope and Gas Migration Law

“…In order to study the characteristics of gas migration in anisotropic coal seams, Nian et al established the Coupled Anisotropic Dual-Porosity Model and analyzed the influence of permeability anisotropy and working face stress on gas pressure, gas drainage volume, and effective drainage area [24]. At present, scholars have comprehensively used a variety of methods or monitoring equipment to effectively obtain the evolution laws of overlying strata crack fields, stress fields, displacement fields, deformation, gas seepage, and gas pressure, thus guiding the design and application of directional boreholes in gas drainage [25][26][27]. In addition, according to the dynamic change of gas drainage concentration, it can also be directly used to judge the stress distribution characteristics of the working face [28].…”