Influence radius of gas extraction borehole in an anisotropic coal seam: Underground in‐situ measurement and modeling

Abstract

Coal seam degasification by in‐seam drilling borehole is one of the popular techniques for coal mine methane (CMM) control. How to address the conflict between borehole numbers and drainage durations always arouses researchers’ interests. Furthermore, since coal has anisotropy structures, how the anisotropy feature of coal associated with bedding and cleat structure affects the influence radius of the drainage borehole has rarely been considered. In order to address the above‐mentioned issues, this work not only conducted underground in‐situ measurement of the borehole influence radius within 200 days in an anisotropy coal seam at Jiulishan coal mine in China, but also modeled the influence radius evolvement around borehole in an anisotropy coal seam using finite‐element based COMSOL package. The underground in‐situ measurement revealed an anisotropy feature of borehole influence radius associated with coal bedding and cleat structures. The influence radius of borehole parallel to the bedding plane in butt cleat direction is much larger than that perpendicular to the bedding plane. Ten permeability measurements of coal show that the permeability of coal parallel to the bedding plane in butt cleat direction is higher than that perpendicular to the bedding plane. Simulation results of the gas transport model in coal are consistent with underground in‐situ measurement in determining the influence radius of drainage borehole in the anisotropy coal seam. Based on modeling results, the ellipse influence area of borehole in an anisotropy coal seam is proposed, and the relationship between the influence radius of borehole and drainage time is obtained. On the basis of these findings, the proper in‐seam borehole arrangements for a specific mining panel at different drainage durations are determined. The finding of this work will be fundamental for addressing the conflict between minimizing the cost of borehole arrangement and increasing coal mining productions by adjusting CMM drainage durations.

Theoretical, numerical, and experimental analysis of effective extraction radius of coalbed methane boreholes by a gas seepage model based on defined criteria

“…The variation of gas pressure with the extraction or mining pressure relief is continuously observed until the gas pressure measurement is completed. When the measured gas pressure drops to a safe range, the effective extraction radius of boreholes can be obtained more accurately by the gas pressure method . In accordance with the Regulations on Prevention and Control of Coal and Gas Outburst, the effective extraction radius can be determined at the maximum gas pressure (0.74 MPa), the maximum gas content (8 m 3 /t), or the gas content decreased by more than 30% .…”

“…At present, the main methods for calculating the effective extraction radius are theoretical calculation, 28,29 field measurement 14,27 and numerical simulation. 30,31 Zhang et al 32 concluded that the extraction radius increased nonlinearly with the borehole radius, while Kong et al 33 found that the relationship between the extraction radius and the borehole radius was linear. This difference in research results is mainly due to the lack of in-depth discussion and unification of the effective extraction radius evaluation criteria.…”

“…Year Others Electromechanical Transportation Blasting Fire Gas Floor by the gas pressure method. 25,27,31,40,41 In accordance with the Regulations on Prevention and Control of Coal and Gas Outburst, the effective extraction radius can be determined at the maximum gas pressure (0.74 MPa), the maximum gas content (8 m 3 /t), or the gas content decreased by more than 30%. 42 However, most researchers only considered one or two of these criteria, not all the three criteria, to evaluate the effective extraction radius, which leads to inaccurate results.…”

Failure mechanism and fracture aperture characteristics of hard thick main roof based on voussoir beam structure in longwall coal mining

“…According to Equation (9), the expressions of the obtainable coefficients A, B, C, D, and F can be solved, along with the relation between E and G:…”

“…In addition, mining-induced fracture aperture is the main channel for aquifer water inrush and gob gas migration. [6][7][8][9] Understanding the failure mechanisms and fracture aperture characteristics plays an important role for establishing a working face early warning system.…”