A Gas Seepage Modeling Study for Mitigating Gas Accumulation Risk in Upper Protective Coal Seam Mining Process

Cun Zhang,Mingxue Li,Chen Wang,Lei Zhang

doi:10.1155/2018/8127207

Cun Zhang, Mingxue Li + Show 2 more

Open Access

https://doi.org/10.1155/2018/8127207

Copy DOI

Abstract

Protective coal seam mining (PCSM) is one of the most significant mitigation measures of regional outburst in the process of deep coal seam mining, which has high outburst risk in China. During the PCSM process, the phenomenon of methane concentration exceeding the limit usually occurs in the working face. It is vital to understand factors affecting gas emission from the protective seam working face (PSWF) and to obtain an equation for determining the quantity of gas emission. A gas seepage model (GSM) was developed to simulate the gas emission during the process of upper PCSM. In this study, an equation was formulated to determine the quantity of gas desorbed from the protected seam into PSWF. These equations have been developed by using Fick’s second law of diffusion and Darcy’s flow law. The relationship between permeability and stress was described in an elastic-plastic state, and the mechanics of surrounding rock were investigated. It can be concluded from GSM that the initial gas pressure of protected seam, the characteristics of interlayer rocks, and the ventilation pressure of PSWF were the main factors that influenced the desorption of gas emission from the protected seam into PSWF. The developed GSM was tested for calculating gas emission quantity from the PCSM process by utilizing the actual geological condition data of a coal mine, which is located in Hancheng, China. The results have shown great agreement with obtained field measurements, which is done by combining the fitting curve of ventilation air methane quantity for PSWF with an interlayer spacing. A loss coefficient (δ) of 1.012 × 10−3 was obtained in this study.

Highlights

Coal and gas outburst accident is a complex dynamic phenomenon, which occurs frequently in coal mines in China
Many research studies have been conducted nationally. These studies have elucidated the outburst mechanism in coal and gas; outburst risk indexes and mitigation measures have been proposed in these studies [4,5,6]
During protective coal seam mining (PCSM), the phenomenon of methane concentration exceeding the limit usually occurs in the protective seam working face (PSWF)

Summary

Introduction

Coal and gas outburst accident is a complex dynamic phenomenon, which occurs frequently in coal mines in China. Protective coal seam mining (PCSM) is preferentially used to release coal seam pressure and enhance permeability. It is one of the main outburst mitigation measures in China, mainly because gas content and its associated outburst risk are relatively low. During protective coal seam mining (PCSM), the phenomenon of methane concentration exceeding the limit usually occurs in the protective seam working face (PSWF). Because the protected seam offers gas pressure relief, a large amount of gas is desorbed and flows into PSWF This is the main reason why methane concentration exceeds the limit in the PCSM process. More attention is paid to pressure relief effect of the protected seam, but factors causing methane concentration to exceed the limit are ignored during PCSM [13, 14]. The results indicate that the established GSM completely agreed with obtained field measurements

Previous Studies on the Evolution Law of Permeability

Gas Seepage Model of Upper Protective Seam Mining

Analysis of Floor Failure Depth

Gas Seepage Model Verification

Discussions

Conclusions