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首页> 外文期刊>Environmental earth sciences >A new method to evaluate the brittleness for brittle rock using crack initiation stress level from uniaxial stress-strain curves
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A new method to evaluate the brittleness for brittle rock using crack initiation stress level from uniaxial stress-strain curves

机译：利用单轴应力-应变曲线的裂纹萌生应力水平评估脆性岩石脆性的新方法

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摘要

Brittleness has been a prevalent descriptor in rock mass engineering and formation fracturing stimulation. Here a new definition of mechanical brittleness index as crack initiation stress level (sigma(ci)/sigma(c)) is proposed and verified with diorite, granite, marble, sandstone, and shale samples using uniaxial compressive strength (UCS) test. Regression analysis reveals obvious correlation between sci/sc and four brittleness definitions based on UCS and Brazilian tensile strength (BTS) (B19 = sigma(c)/sigma(t), B20 = (sigma(c) - sigma(t))/(sigma(c) + sigma(t)), B21 = (sigma(c) x sigma(t))/2, B22 = (B21)(1/2)). For diorite, granite, marble, and sandstone, significant relationships exist between B19, B20, and B23; however, for anisotropic shale, obvious relationships were found between B21, B22, and B23. It is suggested that sigma(ci)/sigma(c) can well reflect the heterogeneity and anisotropy of rock and the correlation between B19, B20, B21, B22, and sigma(ci)/sigma(c) depends on the rock structural fabric. In addition, rock with high brittleness generally has a lower sci/sc value and fracture easily occurs during sample deformation. It is not the case that formation with higher brittleness is considered as good fracturing candidates. Fracture pattern was obtained for shale samples from X-ray CT scanning, and the results reveal that fracture density is the maximum for sample with the lowest sigma(ci)/sigma(c) value. The most striking finding is that there exists a good correlation between the stimulated fracture density and sigma(ci)/sigma(c), and it implies that a good formation for hydraulic fracturing is not of high brittleness. The proposed brittleness index would be helpful to evaluate the formation fracability and screen hydraulic fracturing candidates.
机译：脆性一直是岩体工程和地层压裂增产中的普遍描述。在这里，提出了一种新的机械脆性指数定义为裂纹萌生应力水平（sigma（ci）/ sigma（c）），并使用闪长岩，花岗岩，大理石，砂岩和页岩样品通过单轴抗压强度（UCS）测试进行了验证。回归分析显示，基于UCS和巴西抗拉强度（BTS）（B19 = sigma（c）/ sigma（t），B20 =（sigma（c）-sigma（t））/ （sigma（c）+ sigma（t）），B21 =（sigma（c）x sigma（t））/ 2，B22 =（B21）（1/2））。对于闪长岩，花岗岩，大理石和砂岩，B19，B20和B23之间存在显着关系。但是，对于各向异性页岩，在B21，B22和B23之间发现了明显的关系。建议sigma（ci）/ sigma（c）可以很好地反映岩石的非均质性和各向异性，并且B19，B20，B21，B22和sigma（ci）/ sigma（c）之间的相关性取决于岩石的结构。另外，具有高脆性的岩石通常具有较低的sci / sc值，并且在样品变形期间容易发生破裂。并非具有较高脆性的地层被认为是良好的压裂候选者。通过X射线CT扫描获得页岩样品的断裂模式，结果表明，具有最低sigma（ci）/ sigma（c）值的样品的断裂密度最大。最惊人的发现是，受激裂缝密度与sigma（ci）/ sigma（c）之间存在良好的相关性，这表明水力压裂的良好地层并不具有高脆性。建议的脆性指数将有助于评估地层易碎性和筛选水力压裂候选物。

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  • 来源
    《Environmental earth sciences》 |2017年第23期|799.1-799.18|共18页
  • 作者

    Wang Y.; Li C. H.; Hu Y. Z.; Zhou X. L.;

  • 作者单位

    Univ Sci & Technol Beijing, Beijing Key Lab Urban Underground Space Engn, Dept Civil Engn, Sch Civil & Resource Engn, Beijing 100083, Peoples R China;

    Univ Sci & Technol Beijing, Beijing Key Lab Urban Underground Space Engn, Dept Civil Engn, Sch Civil & Resource Engn, Beijing 100083, Peoples R China;

    Chinese Acad Sci, Key Lab Shale Gas & Geoengn, Inst Geol & Geophys, Beijing 100029, Peoples R China;

    Univ Sci & Technol Beijing, Beijing Key Lab Urban Underground Space Engn, Dept Civil Engn, Sch Civil & Resource Engn, Beijing 100083, Peoples R China;

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  • 正文语种 eng
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  • 关键词

    Brittleness index; Crack initiation stress; Uniaxial compressive test; Hydraulic fracturing;

    机译：脆性指数裂纹萌生应力单轴压缩试验水力压裂;

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