Hydraulic Fracture Vertical Propagation Mechanism in Interlayered Brittle Shale Formations: An Experimental Investigation
Hydraulic Fracture Vertical Propagation Mechanism in Interlayered Brittle Shale Formations: An Experimental Investigation
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DOI：
10.1007/s00603-022-03094-1
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发表时间：
2022-10
影响因子：
6.2
通讯作者：
Jun Zhang;Qian Yu;Yuwei Li;Z. Pan;Bob Liu
中科院分区：
文献类型：
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作者：
Jun Zhang;Qian Yu;Yuwei Li;Z. Pan;Bob Liu
为了研究中国东北松辽盆地南部青衣段层间脆性页岩地层水力裂缝的垂向扩展机理，设计了一种模拟薄砂岩夹层中页岩的实验模型。该模型反映了页岩和砂岩的力学性质和脆性特征的相对差异。通过一系列真三轴水力压裂实验，结合裂缝面积测量、三维裂缝重建和声发射(AE)监测，定量研究了关键地质和工程因素对页岩夹层裂缝垂向扩展行为的影响。实验结果表明，层间页岩地层中水力裂缝的扩展模式有四种：堵塞型、偏转型、穿透型和复合型。层间倾角与水力裂缝的穿透能力呈负相关，垂直地应力差和界面胶结强度与水力裂缝的穿透能力呈正相关。夹层的脆性特征对水力裂缝的扩展行为有相当大的影响。由于夹层的塑性变形，具有弱脆性的夹层抑制了水力裂缝穿透界面和夹层的能力，从而消耗了相当多的本应用于裂缝扩展的弹性能量。在注入速度和粘度较高的情况下，压裂液在界面的渗透率较小，裂缝尖端积累的水力能量较集中，水力裂缝穿透界面进入夹层的能力增强。研究成果可以加深对陆相层间页岩地层裂缝几何形态和裂缝交汇机理的认识，为压裂参数优化提供更准确的指导。
To investigate the vertical propagation mechanism of hydraulic fractures in interlayered brittle shale formations in the Qingyi member of the Southern Songliao Basin in Northeast China, an experimental model for simulating the shale within thin sandstone interlayers is designed. This model reflects the relative difference of the mechanical properties and brittleness characteristics between shale and sandstone. When combining a series of true triaxial hydraulic fracturing experiments with fracture area measurement, three-dimensional fracture reconstruction, and acoustic emission (AE) monitoring, the effects of the key geological and engineering factors on the fracture vertical propagation behaviors in interlayered shale formations are quantitatively studied. The experimental results showed four types of hydraulic fracture propagation patterns in interlayered shale formation:arresting pattern,deflecting pattern,penetrating patternandcomposite pattern. The interlayer dip angle is negatively correlated with the penetrating ability of the hydraulic fracture, while the vertical in situ stress difference and interface cementation strength are positively correlated with the penetrating ability of the hydraulic fracture. The brittleness characteristics of the interlayer have a considerable effect on the propagation behavior of the hydraulic fracture. The interlayer with weak brittleness inhibits the hydraulic fractures’ ability to penetrate the interfaces and interlayers owing to the plastic deformation of the interlayer, thereby consuming considerably more elastic energy that should have been applied to fracture propagation. Under a higher injection rate and viscosity, the infiltration of the fracturing fluid in the interface is less, the hydraulic energy accumulated at the fracture tip is more concentrated, and the hydraulic fracture’s ability to penetrate through the interface into the interlayer is strengthened. The results of this study can provide a deeper understanding of fracture geometry and the fracture intersection mechanism in the continental interlayered shale formation, providing a more accurate guidance for fracturing parameter optimization.