Numerical Simulation Research on the Pressure Relief and Permeability Enhancement Mechanism of Large-Diameter Borehole in Coal Seam

Abstract

In order to achieve high-efficiency extraction of coal seams with large-diameter borehole and large flow rates, and to rapidly reduce coal seam gas content and pressure, a large-diameter borehole coal seam pressure relief and permeability enhancement technology is proposed. In this paper, numerical simulation is used to study the mechanism of pressure relief and permeability enhancement in coal seams with large-diameter boreholes, and the evolution of stress, cracks, gas, and permeability of coal bodies around boreholes with different diameters is discussed. The research results show that the stress changes in the coal body around the borehole are symmetrically distributed around the borehole. The stress evolution controls the evolution of the coal body’s cracks. Firstly, damage occurs around the borehole and then extends to the upper left and right corners, like a butterfly spreading its wings. The crushing zone increases with the increase of the hole diameter, and the impact radius of the 100-mm, 200-mm, 300-mm, and 350-mm diameter borehole rupture is 0.375 m, 0.65 m, 1.0 m, and 1.25 m, respectively. The rupture radius of the double 350-mm diameter borehole can reach 2.4 m. The larger the diameter of the borehole, the more fissures will be produced, and the air permeability of the coal body in the affected coal seam area will obviously increase. The research results provide theoretical support for gas drainage in soft, low-permeability, high-gas coal seams.

Study on reasonable loading mode of small-scale roadway model and its application in mining engineering

“…Moreover, in the application of existing small-scale models, there is no unified conclusion on the application of loads. Some scholars use stress load (Nian et al, 2022), and others use displacement load (Li et al, 2022).…”

“…However, there is no unified conclusion on the load mode in the roadway model. Some scholars use stress load (Zhu et al, 2013; Fan et al, 2019; Nian et al, 2022), and others use displacement load (Wang, 2005; Li et al, 2022; Yuan et al, 2022). Therefore, the determination of the load mode in the roadway model is an important factor affecting the accuracy of the results.…”

“…Compared with the large-scale stratum model, the load mode of the small-scale roadway surrounding rock model is not clear, and the existing small-scale model has both stress load and displacement load. Fan et al (2019), Nian et al (2022) and Zhu et al (2013) applied stress loading on the upper boundary of the model to carry out numerical simulation of roadway surrounding rock. Li et al (2022), Wang (2005) and Yuan et al (2022) applied displacement load on the upper boundary of the small-scale model to study the properties of surrounding rock, anchorage body and drilling pressure relief of deep surrounding rock.…”