兰恒星, 伍宇明, 李全文, 陈俊辉, 赵晓霞. 2017: 龙马溪组页岩三维缝网重构及分形分析. 工程地质学报, 25(6): 1557-1565. DOI: 10.13544/j.cnki.jeg.2017.06.019
    引用本文: 兰恒星, 伍宇明, 李全文, 陈俊辉, 赵晓霞. 2017: 龙马溪组页岩三维缝网重构及分形分析. 工程地质学报, 25(6): 1557-1565. DOI: 10.13544/j.cnki.jeg.2017.06.019
    LAN Hengxing, WU Yuming, LI Quanwen, CHEN Junhui, ZHAO Xiaoxia. 2017: RECONSTRUCTION AND FRACTAL ANALYSIS FOR THREE DIMENSIONAL FRACTURE NETWORK OF LONGMAXI SHALE. JOURNAL OF ENGINEERING GEOLOGY, 25(6): 1557-1565. DOI: 10.13544/j.cnki.jeg.2017.06.019
    Citation: LAN Hengxing, WU Yuming, LI Quanwen, CHEN Junhui, ZHAO Xiaoxia. 2017: RECONSTRUCTION AND FRACTAL ANALYSIS FOR THREE DIMENSIONAL FRACTURE NETWORK OF LONGMAXI SHALE. JOURNAL OF ENGINEERING GEOLOGY, 25(6): 1557-1565. DOI: 10.13544/j.cnki.jeg.2017.06.019

    龙马溪组页岩三维缝网重构及分形分析

    RECONSTRUCTION AND FRACTAL ANALYSIS FOR THREE DIMENSIONAL FRACTURE NETWORK OF LONGMAXI SHALE

    • 摘要: 传统上研究含气页岩宏观缝网特征的方法多是基于小样品开展,通过观察小样品的裂缝展布特征来了解页岩的裂缝发育的宏观特性。但是这类方法因尺度过小,缺乏代表性,不能获取连续面上的裂缝特征,难以分析裂缝发育和地应力方向之间的关系。为获取更详细的大尺度含气页岩的宏观裂缝特征,本文从重庆市涪陵地区石柱县采样获取2m×3m×0.7m完整大尺度岩块,并采用有序标号切割来获取30cm3规格岩样,在此基础上提取小岩样的表面裂缝并按照大尺度岩样切割的相对顺序构建三维裂缝网络。分析观测大尺度的三维裂缝网络可以发现,含气页岩的裂缝分布具有明显的规律性:水平主应力方向上的裂缝发育度普遍高于最小水平主应力方向;垂直方向上的裂缝与最小水平主应力的夹角为-62°。分维研究表明所有不同面上的裂缝均符合分维特性,说明小尺度裂缝特征和大尺度裂缝特征具有相似的规律性。此外,研究还表明最大水平主应力上的裂缝密度和分形维数最大,缝网结构最为复杂,最小水平主应力方向缝网结构次之,垂直主应力方向的裂缝结构最为简单;水平应力方向上主要以层理裂缝为主,垂直方向上以剪切缝为主,且与最小水平主应力的夹角为-62°。在掌握宏观裂缝分布特征基础上,研究可为页岩显微观测实验提供相应的理论依据。

       

      Abstract: Recent studies were based on the small samples which were as big as core samples to get the fracture propagation features. However, the small samples had many limitations. For example, continuous fracture propagation characteristics were difficult to get, which means it was a tough work to analyze the relationship between in-situ stress and fracture distribution. Hence, fracture propagation characteristics were gathered from a 2m×3m×0.7m samples from Shizhu County, Chongqin. The sample was cut into several cubic samples whose lengths of the sides were 30cm. At the same time, every surface of the cubic sample is numbered. Then the fracture distribution characteristics on each surface of the samples is obtained. The 3D fracture network is rebuilt according to the surface number. The fracture network shows the obvious rules that there are more fractures on the surface in the principle stress direction in contrast to other directions. The fractures on the surface perpendicular to the principle stress are 62°to the principle stress direction. Research on the fractal dimension proves that fractures on the different surfaces conform to the fractal dimension feature, which indicates that fractures' structure in small scale and big scale have similar regularity. In addition, fracture density and fractal dimension number in the maximum principle stress direction are bigger than other directions, which means fracture network structure is more complex. And fracture network structure in the surface perpendicular to the principle stress is less complex than that in the minimum horizontal stress direction. There are more bedding fractures in the horizontal stress direction while more shear fractures in the vertical direction, which are-62°to the minimum horizontal principle stress direction.

       

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