Experimental Study on Gas Seepage Characteristics of Axially Unloaded Coal under Different Confining Pressures and Gas Pressures

Abstract

Protective coal seam mining can not only effectively prevent coal and gas outbursts in mines, but also provide stress unloading space for the protected coal seam. The coal body in the protected coal seam might undergo deformation, internal damage and structural damage, which changes its gas seepage characteristics. This study aims to explore the variations of permeability of the coal body in the protected coal seam under axial unloading. With the coal body from the outburst coal seam in the Huaibei mining area as the research object, experiments were conducted to explore the gas seepage characteristics of axially unloaded coal body under different confining pressures and gas pressures, using the TAWD-2000 coal-rock mechanics-seepage experimental system. According to the results, with respect to the gas seepage, the variations of permeabilities of axially unloaded coal samples are closely related to their deformation and damage. As the confining pressure and gas pressure rise, the difference between the permeability at the final failure point and the initial permeability rises at a decreasing rate. The experiments fully demonstrate that the protective coal seam is technically important for the unloaded gas drainage and the coal and gas outburst prevention of the protected coal seam. Under different confining pressures and gas pressures, the permeability of axially unloaded coal varies to different extents and at different rates. The mining scheme for the protective coal seam should be designed in accordance with its confining pressure and gas pressure. This study is of guiding significance for the prevention and control of coal and gas outbursts in coal seam groups.

RETRACTED ARTICLE: Analysis of fractured soft rock characteristics in fault rupture zones and laneway shoring

“…The area surrounding a fractured rock mass is complex and has the property of being between solid and fluid, which is a common type of special carrier in many geological engineering applications. Underground engineering disasters are caused by 1 – 3 fractured rock formations resulting from changes in the original stress field and redistribution of rock stress, which affect the stress distribution in the rock formation. Internal pore pressure and complex hydrogeological conditions primarily cause such fractures.…”

A Study of the Effect of Freeze–Thawing by Liquid Nitrogen on the Mechanical and Seepage Characteristics of Coal with Different Moisture Content Values

“…The decimal classification of pore size proposed by BHODB classifies pores into micropores (diameter < 10 nm), transition pores (diameter 10-100 nm), mesopores (diameter 100-1000 nm), and macropores (diameter > 1000 nm), with micropores and transition pores, also called adsorption pores, serving as the main storage space. Mesopores and macropores serve as the main flow paths for fluids and are called percolation pores [26][27][28][29], and the flow of fluids through these pore fractures is referred to as percolation. In order to recover the original stress state of the coal sample, the experiment was started by increasing the surrounding pressure to 9 MPa at a radial loading rate of 0.02 MPa/s and then adding 1 MPa of high-purity nitrogen; the axial loading test was started after the gas flow was stabilized.…”

Optimization of drilling parameters for coal seam gas extraction considering fluid–solid coupling and field application

“…Gas disaster is one of the important factors threatening the safety production of coal mines 1–3 4–6 …”

“…The intrinsic factor affecting the gas flow in the coal body is the change of permeability in the coal seam. The effective stress sensitivity coefficient is used to characterize the effect of the gas seepage process on the strain of the coal body, and the permeability sensitivity coefficient is higher than the surrounding pressure in the axial seepage process, and the sensitivity coefficient of gas pressure is higher than the permeability in the radial seepage process 3 13–16 …”

“…The effective stress sensitivity coefficient is used to characterize the effect of the gas seepage process on the strain of the coal body, and the permeability sensitivity coefficient is higher than the surrounding pressure in the axial seepage process, and the sensitivity coefficient of gas pressure is higher than the permeability in the radial seepage process. 3 Stress variation is closely related to coal rock body permeability deformation, and the stress of coal seam is obtained to get different sizes of permeability area, and based on this area can effectively design more efficient gas extraction drilling. [13][14][15][16] The variation of coal seam permeability is a geological factor that affects the efficiency of gas extraction, therefore, it is necessary to design boreholes with reasonable parameters to effectively coal seam gas concentration.…”