射孔对页岩水力裂缝形态影响的物理模拟实验

Experimental investigation on the influence of perforation on the hydraulic fracture geometry in shale

通过XRD、扫描电镜及力学强度测试等实验对龙马溪组页岩的物理力学性质进行分析,并采用真三轴压裂改造模拟器开展水平井水力压裂物理模拟实验,探究射孔参数及页岩物理力学性质对裂缝形态的影响规律。实验结果表明:(1)具有3种不同射孔类型的试样,在压裂后主要形成4种水力裂缝的形态模式,其中组合型射孔对于复杂裂缝的形成具有一定的促进作用。当射孔间相位角和间距过小时,缝间应力干扰增大,不利于扩大裂缝规模。(2)试样在压裂过程中的泵压-时间曲线,会因射孔类型的不同而呈现出明显的差异,曲线的波动程度和裂缝的复杂程度呈一定的正相关。(3)水力裂缝在延伸过程中与结构面相交时出现的穿透、分叉等现象是形成裂缝网络的前提。各向异性、微裂缝和微孔隙、脆性指数等页岩的物理力学性质会影响裂缝的扩展路径和迂曲度。

The physical simulation experiment of hydraulic fracturing is an effective way to obtain the geometry and propagation criterion of hydraulic fractures.The physical and mechanical properties of the Longmaxi shale were investigated by using XRD,scanning electron microscope,strength test and other experiments.Moreover,the tri-axial fracturing simulator has been used to study the effects of physical and mechanical properties of shale,and the perforation on the fracture geometry.The results show that：（1）Four types of hydraulic fractures corresponding to three types of perforation are summarized,in which the combination type perforation has a certain promotion effect on the formation of complex fractures.When the phase angle and spacing between perforations are too small,the interference between fractures is enhanced,which is not conducive to increasing the fracture scale.（2）The pressure-time curves show obvious differences due to the different types of perforation.The fluctuation degree of the curve and the complexity of fractures have a positive correlation to a certain extent.（3）The penetrating,branching of hydraulic fractures are the precondition for the formation of fracture networks when they intersect with the structural plane.The physical and mechanical properties such as anisotropy,micro fractures,brittleness index will affect the propagation path and the tortuosity of hydraulic fractures in shale.