3D imaging characteristics of pore and fracture of tight sandstone in Baihetan reservoir area based on μCT technology
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摘要:
微焦点X射线CT扫描(μCT)技术作为实现岩石内部孔-裂隙结构可视化最有效的方法之一, 仍需进一步探究其在致密砂岩孔-裂隙三维成像应用中的有效性。以白鹤滩水电站坝址区致密砂岩为例, 通过超高精度μCT技术与分割算法, 探究了不同扫描精度下试样的孔-裂隙三维成像特征, 并进一步结合扫描电子显微镜(SEM)测试分析了其对获取关键结构信息的影响。结果表明: 交互式阈值法和Top-hat组合的分割法可更精细化的提取致密砂岩孔-裂隙信息, 其中交互式阀值法适用于较大孔-裂隙提取, Top-hat法适用于微小裂隙提取; 致密砂岩结构中微小孔隙、微裂纹十分发育, 且孤立孔隙较多; 0.62μm相对于1.5μm的扫描分辨率呈现了更加清晰的孔隙网络模型, 但由于纳米级的测试范围受限, 关键结构信息特征可能被放大化; 当扫描分辨率大于2μm时, 关键微结构信息可能被忽略。因此, 在致密砂岩孔-裂隙三维特征研究中, 应采用较高的扫描精度并进行多区域信息采集, 以有效的揭示关键微结构特征, 这一基础性工作为进一步有效地揭示致密岩石结构演化信息提供了支撑。
Abstract:Microfocus X-ray CT scanning (μCT) is one of the most effective methods for visualization of pore-fracture structure in rock, and its effectiveness in 3d imaging of pore-fracture in tight sandstone should be further explored.Taking the tight sandstone at the dam site of Baihetan Hydropower Station as an example, the pore-fracture 3D imaging characteristics of samples with different scanning accuracy were explored by using ultra-high precision μCT technology and segmentation algorithm, and their influence on obtaining key structural information was analyzed by SEM test.The results show that the combined segmentation method of interactive threshold and Top-hat can extract the pore and fracture information of tight sandstone more accurately. The interactive threshold segmentation method is suitable for the extraction of large pore and fracture, and the Top-hat segmentation method is suitable for the extraction of small pore.Small pores and microcracks are very developed in tight sandstone structure, and there are many isolated pores. Compared with 1.5 μm scanning resolution, 0.62 μm scanning resolution presents a clearer pore network model, but due to the limited testing range at the nanoscale, the key structural information properties may be magnified.Critical microstructure information may be missed when the scanning resolution is greater than 2μm.Therefore, in the study of three-dimensional characteristics of pores and fractures in tight sandstone, high scanning accuracy should be selected and multi-region information acquisition should be carried out to effectively reveal the key microstructure features. This basic work provides a support for further effectively revealing the structural evolution information of tight rocks.
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Key words:
- Baihetan hydropower station /
- pore-fracture /
- tight sandstone /
- μCT technology /
- scanning accuracy
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图 3 白鹤滩坝址区小坝组砂岩矿物成分及质量分数
Figure 3. Mineral composition and mass percentage of Xiaoba Formation sandstone in Baihetan Dam site
图 4 蔡斯Xradia-520-Versa 3D X射线显微镜扫描现场测试图
Figure 4. Field scan test image of Chase Xradia-520-Versa 3D X-ray microscope
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