煤与瓦斯共采钻孔增透半径理论分析与应用

在煤与瓦斯共采时,受采动加、卸载应力影响,瓦斯抽采钻孔围岩塑性区内煤体会产生大量裂隙,增大了瓦斯的渗透率,形成瓦斯增透圈,增透圈半径的大小直接影响瓦斯的抽采效果。以钻孔围岩"蝶形塑性区"理论为基础,建立了钻孔塑性区与瓦斯增透圈模型,首次推导出了钻孔增透圈半径解析式。深入分析了钻孔增透半径影响因素发现:增透半径与钻孔半径成线性正比例关系,与最小围压和围压比值呈类指数增长关系,与岩石黏聚力和内摩擦角呈负指数变化关系;其中最小围压与围压比值是影响增透半径的关键因素,深部开采与高围压比值是形成大尺寸有效增透圈的必要和充分条件。这一理论为煤与瓦斯共采中瓦斯抽采钻孔间距设计、位置选择、方向确定、采场与钻孔布置在时间和空间上关系协调提供了科学依据。

Theoretical analysis and application about permeability-increasing radius of drilling for simultaneous exploitation of coal and gas

Under the influence of mining induced loading and unloading stress in simultaneous exploitation of coal and gas,a large number of cracks are generated in the surrounding rock plastic zone of gas drilling,which increases the permeability of gas and forms the permeability-increasing circle whose radius directly affects the effect of gas extraction.Based on the theory of the “butterfly plastic zone”,the model of the borehole plastic zone and the gas permeability-increasing circle was established,and the analytic formula of permeability-increasing circle radius was deduced.The further research on the factors affecting the permeability-increasing radiusreveals that the permeability-increasing radius is linearly positive to the radius of borehole,similarly exponentially positive to the minimum confining pressure and confining pressure ratio,and exponentially negative to the cohesion and the internal friction angle.The minimum confining pressure and confining pressure ratio are the key factors,and the deep mining and high confining pressure ratio are the sufficient and necessary conditions for the formation of effective permeability-increasing circle.This theory provides ascientific basis for the drilling spacing design,location selection,direction determination and the coordination of time and space between mining field and borehole layout.