Change Characteristics of Negative Drainage Pressure along the Drill Hole: Theoretical Analyses and Field Tests

Abstract

A proper understanding of the change characteristics of negative drainage pressure along a drilling hole is essential since gas drainage parameters are the key parameters that influence the efficiency of gas drainage. In this study, based on the coupling of gas seepage from coal seams and the gas flow along the drilling hole, a theoretical model was established to calculate the gas pressure change law along the drilling hole with different influencing factors. Subsequently, a multibranch method was applied to test the negative pressure at different drilling holes. Finally, a field test was conducted in the Jiulishan coal mine to analyze the changed characteristics of the negative drainage pressure along the drilling hole. The results show that at a constant negative drainage pressure in the borehole, the negative pressure gradually decreased with increasing depth. With an increase in negative drainage pressure at the borehole, the negative pressure loss for every 100 m substantially increased. The gas flux had the most obvious influence on the negative pressure in the drilling hole, and the pressure loss rapidly increased with increasing gas flux. When the diameter of the borehole was small, the negative pressure loss was significant; when the drilling hole was deep, the negative pressure decreased more significantly. This study has important theoretical and practical significance for improving the gas drainage effect.

Study on Effective Extraction Radius of Directional Long Borehole and Analysis of the Influence Mechanism

“…Considering the problem of measuring the effective extraction radius of boreholes, scholars have studied these through theoretical analysis, , numerical simulation, , and field experiments. , In terms of numerical simulation, various scholars worldwide have studied the gas-structure interaction model of gas-containing coal and the factors affecting the effective extraction radius. Liang established a gas-structure coupling model based on the deformation characteristics of the coal skeleton and the adsorption and desorption characteristics of gas.…”

Research on Hole Collapse Monitoring Technology of Coal Seam Gas Extraction Boreholes

“…Under the influence of ground stress and mining, gas extraction boreholes are prone to collapse and deformation, which seriously affects gas management [10,11]. Borehole monitoring is a prerequisite to solving the problem of borehole collapse, can obtain the status information of the borehole, and can effectively prevent the occurrence of borehole collapse, as well as provide services to optimize the arrangement of the borehole, playing a positive role in deepening the process of drilling refinement operation, and greatly improving the effect of gas extraction in a borehole [12][13][14][15]. In order to meet the increasingly rigorous engineering research environment and achieve the goal of accurate drilling support, it is important to carry out research on accurate monitoring of the in-hole conditions of gas extraction boreholes.…”