煤层瓦斯抽采钻孔失稳的延迟效应分析

Delayed Effect Analysis of Gas Extraction Boreholes Instability in Coal Seam

针对富含节理裂隙的煤层瓦斯抽采钻孔结构失稳的延迟现象,分析了瓦斯抽采钻孔周边的瓦斯流场和节理裂隙场。研究表明钻孔结构失稳是由瓦斯孔隙压力和节理裂隙共同影响的;瓦斯孔隙压力的变化会影响节理裂隙表面的正应力,增加节理裂隙发育、扩展、破坏的可能性,宏观表现为钻孔结构的失稳;瓦斯抽采钻孔结构失稳时间上的延迟效应内因是由于煤层节理裂隙的存在,外因则是煤层节理裂隙中瓦斯孔隙压力的变化。最后结合实例说明瓦斯抽采钻孔结构延迟失稳能造成瓦斯抽采浓度、抽采流量的大幅度下降等问题。

Aiming at the delay phenomenon of gas extract borehole structural instability in rick jointed coal seam, this paper analyzed gas flow field and jointed cracks field around gas extraction boreholes. The results showed that the drilling structural instability is the c, ombined effect of gas pressure and joint cracks, the change of gas pressure would affect normal stress of jointed cracks surface, in- creasing the possibility of jointed cracks development and failure, and the performance was borehole instability in the macroscopic. The internal cause of the instability delay of gas extraction boreholes is the existence of the jointed cracks in coal seam, and external cause is gas pressure changes in jointed seam. With practical examples, this paper illustrated that the instability delay phenomenon of gas ex- traction drilling could cause gas extraction concentration and flow decimated and other drilling failure problems.