孔间距对深部煤层钻孔周围裂隙演化及封孔深度的影响

Influence of Borehole Spacing on Evolution of Circumferential Fracture and Sealing Depth of Deep Coal Seam Boreholes

为提高深部低渗透煤层瓦斯的抽采效率和效果,最易实现的方法是缩小钻孔间距,但在实际应用中存在瓦斯浓度衰减快的问题。为剖析其本质原因,以某矿深部煤层钻孔为背景,采用ABAQUS软件对不同间距钻孔形成过程中的裂隙分布情况进行分析。结果表明:巷道松动圈裂隙带分布在巷道周围7.3 m范围内;钻孔施工后,钻孔裂隙区与巷道裂隙区发生叠加;钻孔间距为2、1、0.5 m对应的钻孔间裂隙沟通长度分别为8、10.5、17 m,裂隙沟通效应显著,形成了钻孔漏风通道。通过拟合发现,随着钻孔间距的减小,钻孔裂隙沟通面积的增量呈线性增加,而封孔深度呈指数增长。现场试验表明,当钻孔间距为0.5 m时,封孔深度18 m的钻孔比封孔深度为9 m的钻孔瓦斯纯流量增加1.65倍,有效提高了瓦斯抽采效果。

In order to improve the efficiency and effect of gas extraction in deep low-permeability coal seams,the easiest way to achieve is to reduce the borehole spacing,but there is a problem of fast attenuation of gas concentration in practical applications.In order to analyze its essential causes,the ABAQUS software is used to analyze the fracture distribution during the formation of different spacing boreholes in the background of deep coal seam drilling in a coal mine.The results show that the fracture zone of the roadway loose circle is distributed within the range of 7.3 m around the roadway.After the boreholesare constructed,the boreholes fissure area and the roadway fissure area overlap.The fracture communication length between boreholes corresponding to the spacing of 2 m,1 m and 0.5 m is 8 m,10.5 m and 17 m,respectively.The fracture communication effect is significant,the borehole air leakage channel is formed.Through fitting,it is found that with the decrease of borehole spacing,the increment of borehole fissure communication area increases linearly,while the borehole sealing depth increases exponentially.The field test shows that when the borehole spacing is 0.5 m,the net gas flow rate of the hole with the borehole sealing depth of 18 m is 1.65 times higher than that of the borehole with the borehole sealing depth of 9 m,which effectively improves the gas drainage effect.