Abstract

Accurately determining the height of the gas-guiding fracture zone in the overlying strata of the goaf is the key to find the height of the long horizontal borehole in the roof. In order to determine the height, in this study we chose the 6306 working face of Tangkou Coal Mine in China as a research example and used both the theoretical model and discrete element method (DEM) numerical simulation to find the height of the gas-guiding fracture zone and applied the height to drill a long horizontal borehole in the roof of the 6303 working face. Furthermore, the borehole was utilized to deep into the roof for coalbed methane drainage and the results were compared with conventional gas drainage measures from other aspects. The height of the gas-guiding fracture zone was found to be 48.57 m in theoretical model based on the bulk coefficient and the void ratio and to be 51.19 m in the DEM numerical simulation according to the temporal and spatial variation characteristics of porosity. Taking both the results of theoretical analysis and numerical simulation into consideration, we determined that gas-guiding fracture zone is 49.88 m high and applied it to drill a long horizontal borehole deep into the roof in the 6303 working face field. Compared with conventional gas drainage measures, we found that the long horizontal borehole has the high stability, high efficiency and strong adaptability for methane drainage.

Highlights

  • Coalbed methane (CBM) refers to methane released from the coalbed during and after its mining.With the increase of coal mining depth and coal production in China, CBM-induced accidents occur more frequently and seriously, posing a huge threat to coal mine safety production

  • According to the movement and failure features of overlying strata affected by mining, the empirical formula used to calculate the height of the mining-induced fracture zone is shown as follows: HII =

  • Since the key to the two gas drainage measures is to determine the height of the gas-guiding fracture zone, through theoretical analyses, the heights of both the caving-in zone and the mining-induced fracture zone are found to be 16.3 m and 33.27 m, respectively

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Summary

Introduction

Coalbed methane (CBM) refers to methane released from the coalbed during and after its mining. Proposed and used a CBM drainage gallery drilled into the coalbed situated above or below the worked seam prior to its longwall excavation [13] Both the high level roof boreholes and high level roof roadways are two most commonly used methods for coalbed gas drainage and gas limit control by the mining-induced fracture zone [14]. This method has a series of advantages including the large drainage volume, short construction period, and low mining cost [1,17], and overcomes the shortcomings of commonly used gas drainage measures. This method is of significance for the coal mine to use an accurate long horizontal borehole drilled into the roof to improve the methane drainage efficiency, reduce gas accidents, and ensure safety production

Geological and Mining Conditions of Tangkou Coal Mine
Theoretical Analysis of Gas-Guiding Fracture Zone Height
Particle Discrete Element Software PFC2D Principle
Macroscopic and Fine Parameter Selection and Inversion
Working Face Numerical Model and Measure Arrangement
Analysis of Fissure and Porosity Changes
Gas-Guiding Fracture Zone Division
Design of Methane Drainage Measures
Comparative Analysis for Two Measure Gas Drainage Effects
Findings
Conclusions
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