Research On Determination Method Of Effective Radius Of Gas Extraction In Bedding Borehole And Optimization Of Parameters Of Hole Arrangement

Gas accident is one of the most common and most serious accidents in coal mine safety production.Gas pre-drainage is one of the effective measures to prevent and control gas accidents in coal mines.In Jianxin Coal Mine of Shaanxi Province,gas emission is large,permeability of coal and rock is poor,and gas extraction is.difficult.Making reasonable pre-drainage plan can effectively improve the effect of gas pre-drainage.The effective extraction radius of coal seam is an important parameter for drawing up pre-extraction scheme.The size of effective extraction radius is related to many factors,such as permeability coefficient of coal seam,attenuation coefficient of borehole gas flow,negative pressure of extraction and borehole diameter,etc.Therefore,how to accurately determine the effective gas extraction radius of coal seam is of great value to the formulation of pre-drainage plan,and is of great significance to ensure the safety of coal mine production.Taking 4207 working face of 4-2 coal seam in Jianxin Coal Mine as the research object,this paper,constructs a gas flow model near borehole on the basis of theoretical analysis of gas migration law in coal seam.Then,according to the gas basic parameters measured by coal seam laboratory and using FLUENT simulation software,the gas pressure distribution around borehole is numerically simulated and the borehole diameter,negative pressure of extraction and coal are obtained.The effect of permeability coefficient on effective extraction radius is studied.Then the effective extraction radius of 4-2 coal seam is measured by field measurement.Finally,according to the mining situation of coal seam in this mine,the optimum drilling hole layout scheme for gas extraction is put forward.Through the study,the following conclusions are drawn:with the prolongation of extraction time,the effective extraction radius increases continuously,but the increase rate decreases,and the effective extraction radius has an extreme value;the effective extraction radius has a positive correlation with borehole diameter and coal seam permeability,while the change of negative pressure can not cause significant change of the effective extraction radius.Based on the relationship between gas purity and natural attenuation coefficient of 100-meter borehole,the method of measuring effective extraction radius of coal seam based on residual gas content is improved.The relationship between effective extraction radius and extraction time is established.The effective extraction radius of 94mm borehole and 133mm borehole in 4207 working face of 4-2 coal seam is measured,which is used to build 4-2 coal mine.The design of gas drainage scheme in 4207 working face provides a basis.According to the effective extraction radius measured by field test,the reasonable drilling spacing was numerically simulated by FLUENT simulation software.The influence of different drilling methods on the extraction effect was analyzed,and the reasonable drilling scheme of 4207 working face was put forward.