The quantitative characterization of hydraulic fracture connectivity from a postmortem investigation
The quantitative characterization of hydraulic fracture connectivity from a postmortem investigation
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DOI：
10.1093/jge/gxac012
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发表时间：
2022-04
影响因子：
1.4
通讯作者：
E. Jayawickrama;J. Muto;O. Sasaki;H. Nagahama
中科院分区：
文献类型：
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作者：
E. Jayawickrama;J. Muto;O. Sasaki;H. Nagahama
两个生物硅Onnagawa（ONG I和ONG II）页岩样品已在两个恒定的差应力（分别为60和85 MPa）下进行水力压裂，以研究裂缝网络的连通性演化的事后分析。在圆柱形岩心样品中钻孔内的压力增加到围压（10 MPa）以上，直到水力压裂破坏。两个样品在两种不同的钻孔压力下（ONG I：42 MPa，ONG II：16 MPa）失效。骨折的样本进行扫描，在工业X射线CT机和断层图像的骨折网络提取的尸检调查。从裂缝体积段，通过阈值的裂缝网络的体素值的频率分布，裂缝连通性的定量估计进行了。利用信息论中的裂缝尺寸分布相对熵（${H_r}$）对裂缝的连通性进行了量化。裂缝连通性估计表明，当裂缝显示出具有非常有限的连通性的显著分布时，${H_r}$处于最大值。当形成连通良好的裂缝网络时，${H_r}$的值处于最小值并且接近于0。在这两个样本中，这一最小值是在43 k的阈值下达到的，这表明裂缝网络的最高连通性和最佳代表性。ONG I的裂缝网络表现为多翼水力裂缝网络，而ONG II的裂缝体积较低，已生成平面常规双翼水力裂缝网络。
Two bio-siliceous Onnagawa (ONG I and ONG II) shale samples have been hydraulically fractured under two constant differential stresses (60 and 85 MPa, respectively) to investigate the fracture network's connectivity evolution by a postmortem analysis. The pressure inside the drilled borehole in a cylindrical core sample is increased above the confining pressure (10 MPa) until failure by hydraulic fracture. The two samples failed at two different borehole pressures (ONG I: 42 MPa, ONG II: 16 MPa). Fractured samples were scanned in an industrial X-ray CT machine and the tomographic images of the fracture network were extracted for a postmortem investigation. From the fracture volume segments, obtained by thresholding the frequency distribution of the fracture network's voxel values, a quantitative estimation of fracture connectivity was carried out. The connectivity was quantified based on the relative entropy of size distribution of fractures (${H_r}$), a method adapted from information theory. Fracture connectivity estimation shows that ${H_r}$ is at a maximum value when the fractures show a significant distribution with very limited connectivity. The value of ${H_r}$ is at a minimum and close to 0 when a well-linked fracture network is formed. In both samples, this minimum was attained at the threshold of 43k indicating the highest connectivity and the best representation of the fracture network. The extracted fracture network of ONG I showed a multi-winged hydraulic fracture network while a planar conventional two-winged hydraulic fracture network had been generated in ONG II with a lower fracture volume.