Optimizing Borehole Diameter for Maximum Gas Extraction Efficiency in Coal Seams

Abstract

In mines characterized by high gas concentrations, the process of extracting natural resources frequently precipitates coal and gas outbursts, positioning borehole gas extraction as a pivotal preventative strategy. Investigations aimed at identifying an optimal borehole diameter for gas extraction were undertaken within the Puxi Mine, entailing the drilling of boreholes across a spectrum of diameters and subsequent comparative analysis of the resultant data. This study meticulously evaluated the influence of seven distinct borehole diameters on gas concentration and pure flow rate, per unit length of coal hole and per unit of applied negative pressure. It was discerned that boreholes with larger diameters significantly enhance gas extraction efficacy. Specifically, boreholes of 113mm and 94mm diameters were noted for their exceptional performance, delivering pure flow rates of gas at 0.0215 m³/min and 0.0428 m³/min, respectively. Through a detailed examination of borehole diameters that presented considerable advantages, notably 113mm, 105mm, and 94mm, it was ascertained that the 94mm borehole diameter achieved the highest utilization efficiency, registering a gas pure flow rate of 1.62 × 10 −4 m 3 /min per unit diameter. Consequently, this diameter was identified as the most advantageous for gas extraction purposes. The insights garnered from this investigation are instrumental for the selection of borehole diameters tailored to gas extraction in coal seams of varying thicknesses, and they significantly contribute to the formulation of rationalized gas extraction methodologies.