The Method of Determining Layer in Bottom Drainage Roadway Taking Account of the Influence of Drilling Angle on Gas Extraction Effect

Abstract

The pre-drainage of coalbed methane through boreholes in the bottom drainage roadway (BDR) is the key measure to prevent and control coal and gas outburst. Different arrangement layers in the BDR will make a difference in the range of drilling angle and affect the gas extraction effect. In this paper, the mathematical model of the rock loose circle area around elliptical drilling was constructed. Meanwhile, the fluid–solid coupling model is constructed by using COMSOL software, the dynamic response of coal permeability and volumetric strain with gas pressure and the Klinkenberg effect of gas are considered, and the effect of the change of the elliptical drilling angle on the pressure relief effect of the coal seam is studied. The results showed that the distance between the layer in the BDR and the pre-drainage coal seam would decrease, and the effective extraction length at the same point of gas extraction in the coal seam increases. The area of the rock loose circle and permeability around the drilling decayed negatively and exponentially with the increase in drilling angle. As the drilling angle decreased, the stress in the major axis of the ellipse at the drilling cross-section increased, so the drilling was prone to collapse, and the gas extraction was hindered. Finally, an optimal method of determining the layer in the BDR under the coupling effect of multiple factors was established by combining the measured ground stress. Through field measurement, the drilling extraction rate of the optimized scheme is 60% higher than that of the original scheme.

Research on Pore-Fracture Structure Alteration and Gas Emission Homogenization in an Outburst Coal Seam Induced by CO2 Gas Fracturing

“…Implementing artificial enhanced permeability technologies can effectively improve coal seam gas drainage efficiency, , thoroughly predraining gas from coal seams, and homogenizing gas distribution at the work face, which are fundamental techniques for gas emission homogenization. To achieve this goal, various gas control technologies have been developed and applied globally to address these challenges, including hydraulic fracturing, hydraulic slotting, hydraulic flushing, bottom-up extraction roadway, and deep-hole blasting, − improving gas extraction efficiency to varying degrees. However, research into these technologies has not involved the evaluation of their effects on homogenizing gas emission, which reflects the extraction effect but is more closely tied to the safety and efficiency of production at the work face and is more meaningful for the management of gas in outburst-prone coal seams.…”

Application and Optimization of the Parameters of the High-Level Boreholes in Lateral High Drainage Roadway

“…The gas reserve law in coal mines in China shows the feature of three high (high plasticity structure of coal seam, high gas adsorption ability of coal seam, and high gas content of coal seam) and three low (low gas pressure of coal seam, low gas saturation of coal seam, and low rate of gas permeability of coal seam), which causes the effect of pre-mining gas extraction to be ineffective. Many scholars combine the development characteristics of mining-induced fissures with the migration law of pressure relief gas [6][7][8] and use high drainage roadways and high-level boreholes to extract pressure relief gas [9][10][11][12].…”

Numerical Simulation Study of High-Pressure Air Injection to Promote Gas Drainage

“…In China, the porosity and permeability of coal seams are extremely low [6]. Therefore, it is challenging to pre-drain gas from soft ultra-low permeability coal seams [7,8]. Extremely low coal seam porosity and permeability result in meager gas recovery rates, typically 50% or less [9].…”