Determining the effective extraction radius of coal seam drilling based on standard gas extraction quantity

LI Fei

doi:10.11799/ce202509016

Abstract：Aiming at the challenges in accurately determining the gas extraction radius of coal seams due to the coupled influence of multiple factors,theoretical analysis and field measurements were applied to investigate the decay characteristics of borehole gas flow.The ultimate extraction time of boreholes was derived,and a calculation formula for the extraction radius was established with the constraint of a coal seam gas extraction rate≥30%,providing theoretical and practical foundations for the design of coal seam pre-extraction boreholes.The results indicate:Firstly,the gas extraction flow rate exhibits a negative exponential decay relationship with time,with a gas flow decay coefficient ranging from 0.028 to 0.038 d-1 and an ultimate extraction time of 78.9 to 107.1 d,indicating moderate permeability of the coal seam in the study area.Secondly,at an extraction time of 120 d,the theoretically calculated extraction radius ranges from 2.26 to 2.45 m,while field measurements using the pressure drop method yield an extraction radius of 2.25 m after 115 days of pre-extraction,showing high consistency between theoretical and measured values.Thirdly,at an extraction radius of 2.25 m and an extraction time of 120 d,the residual gas content after pre-extraction is 4.96 m3/t,the extraction rate is 37.37%,the gas pressure reduces by 57.14%,the daily production of the working face is 2780 t/d,and the desorbable gas content after pre-extraction is 3.05 m3/t,complying with relevant requirements for gas extraction.With a borehole diameter of 133 mm,spacing of 4.5 m,extraction negative pressure of 15～20 kPa,and pre-extraction time of 120 d,the gas concentration at the upper corner during mining remains stable at 0.12%to 0.43%,with no gas overrun,demonstrating significant gas control effectiveness.