Horizontal Subzone Characteristics and Methane Seepage Properties of the Gas Flowing Fracture Zone above the Gob

Abstract

Gas flowing fracture zone (GFFZ) is an active zone in the gob where pressure-relieved methane can move freely. However, there are very few research findings on the horizontal development characteristics and internal methane seepage properties of GFFZs. In this paper, based on the development height of a GFFZ above the gob, the GFFZ was horizontally divided into the following: a lateral fracture subzone, an O-ring fracture subzone, and a compacted subzone. e identification criteria for all of these horizontal subzones were given by analyzing the influence of the stress in the coal rock mass on the development of mininginduced fractures. A numerical simulation study was conducted to determine the influences of the mining height and mining depth on the morphological development of all horizontal subzones of the GFFZ, and the simulation results showed that the mining height was the main factor influencing the development characteristics of horizontal subzones of the GFFZ. Both the maximum distance of the lateral fracture subzone beyond the mining boundary and the width of the O-ring fracture subzone increased with the increase of mining height. A physical simulation experiment was performed for extraction of gob methane through a surface borehole, and the experimental results showed that the gas flow state was laminar within the range of the lateral fracture subzone and the compacted subzone but that the gas flow state was turbulent, not following Darcy's law, within the range of the O-ring fracture subzone.

RETRACTED: A new method for layout layer optimization of long horizontal borehole for gas extraction in overlying strata: a case study in Guhanshan coalmine, China

“…Subzone Ⅳ. Compaction fractured subzone: The fractures get gradually closed with the periodic weighting of the main roof. Importantly, research statistics show that (Qin and Xu 2018) the separation fracture rate of 3‰ can be used as the critical value of fracture closure of the broken stratum layer after bearing. The simulation test results (Fig.…”

“…According to the relevant research (Qin and Xu 2018) and simulation test results, when θn is about 3‰, fractures are close to closure, and the broken rock n+1 enters the compaction fractured subzone. Thus, the number of broken rocks in the SFSZ can be obtained by using Eq.…”

Research on the dynamic development of Bed-Separations and ground subsidence based on large-deflection inclined thin-plate model

“…Bed-separation investigations hold significant importance in gas extraction above coal seams [13,14], analysis of water hazards associated with bed separation [15,16], and the practice of Bed-Separation Grout Injection mining. Xu Jialin successfully implemented the simultaneous extraction of coal and gas by extracting the gas from the Bed-separation using the "O" shaped circle of the mining fissure [17,18]. He Jianghui developed a theoretical model in elastic beam mechanics, utilizing the Key Strata theory, to examine the correlation between the dynamic evolution of Bed-separation and the associated water hazards in coal mining within the geological context of the Cretaceous Luohe Formation [19].…”

A new method for layout layer optimization of long horizontal boreholes for gas extraction in overlying strata: A case study in Guhanshan coal mine, China

“…Presently, coal mines in China predominantly employ the LHB technique due to its cost‐effectiveness and high construction efficiency (Figure 1). 17,18 …”

“…The horizontal section of the LHB, situated within the overlying strata, is surrounded by fractures induced by mining, serving as primary pathways for the diffusion, seepage, and extraction of pressure‐relief gas. The total length of LHBs varies from 100 to 1000 m, depending on specific geological conditions and the intended scale of gas extraction from panels 16,18,19 …”