冲击压裂下钻孔极限力学行为规律研究与应用

Research and application of ultimate mechanical behaviorlaw of drilling under impact fracturing

为了研究冲击载荷压裂作用下孔壁受力特征,采用理论分析和试验方法开展不同冲击载荷下孔壁力学行为研究,推导出裂隙的体积应变方程,获得不同冲击载荷下孔壁强度、应变和渗透性变化规律;通过现场抽采实践,探究不同冲击载荷影响钻孔抽采的影响。结果表明:对比p<1.0 MPa试验曲线,当1.0 MPa≤p<10.0 MPa时,试件最大强度降低38.5%,最大应变增加19.5%,最大应变率增加43.4%,试件横、纵裂隙发育,形成径向和环向的裂隙网,渗透通道和数量增加,渗透率呈线性上升;当p≥10.0 MPa时,试件发生冲击破裂,冲击载荷释放,裂隙发育稳定,渗透率趋于稳定;当p=5.0 MPa的钻孔瓦斯抽采时效性是p=0.5 MPa和p=15.0 MPa的2.0倍和3.0倍,初始抽采量是其他两种的1.2倍和2.4倍,在介于极限抗拉载荷和极限抗压载荷之间的冲击载荷作用下,钻孔具有较高透气性和较好稳定性,表现出了高渗透性、高时效性的抽采特征。

In order to study the mechanical characteristics of hole walls under impact load fracturing,theoretical analysis and experimental methods were used to study the mechanical behavior of hole walls under different impact loads.The volumetric strain equation of fracture was derived,and the changing laws of hole wall strength,strain and permeability under different impact loads were obtained.Through the site pumping practice,the influence of different impact loads on drilling and pumping was studied.The results show that:compared with the test curve of p<1.0 MPa,when 1.0 MPa≤p<10.0 MPa,the maximum strength of the specimen decreases by 38.5%,the maximum strain increases by 19.5%,and the maximum strain rate increases by 43.4%.Transverse and longitudinal cracks of the specimen develop,forming radial and circumferential fracture networks,and the permeability increases linearly with the increase of penetration channels and number.When p≥10.0 MPa,impact fracture occurs,impact load is released,crack development is stable,and permeability tends to be stable.When p=5.0 MPa borehole gas extraction timeliness is 2.0 times and 3.0 times of p=0.5 MPa and p=15.0 MPa,the initial extraction volume is 1.2 times and 2.4 times of the other two kinds of gas extraction.Under the impact load between the ultimate tensile load and the ultimate compressive load,the borehole has higher permeability and better stability.It shows the extraction characteristics of high permeability and high timeliness.