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Evaluation of permeability of a fracture system under true triaxial compression

真三轴压缩下裂缝系统渗透率评价

基本信息

批准号：
15206098
负责人：
MATSUKI Koji
金额：
$ 18.47万
依托单位：
Tohoku University
依托单位国家：
日本
项目类别：
Grant-in-Aid for Scientific Research (A)
财政年份：
2003
资助国家：
日本
起止时间：
2003 至 2005
项目状态：
已结题

来源：
https://kaken.nii.ac.jp/en/grant/KAKENHI-PROJECT-15206098/
关键词：
Sheared fracture Large synthetic fracture Permeability of a fracture Fracture aperture Size effect Anisotropy in permeability Heterogeneity in permeability Localization of water flow 真三軸圧縮応力透水性人工き裂引張き裂フラットジャッキ花崗岩せん断変形き

项目摘要

In this study, we performed both experimental studies on permeability of a fracture under true triaxial compression and theoretical studies on aperture and permeability of a fracture utilizing large synthetic fractures of up to 12.8m.Main results obtained by experimental studies can be summarized as follows :1. An experimental system developed in this study can evaluate the heterogeneity in the permeability of a fracture under uniform normal stress for a pore pressure of less than 0.3MPa and shear displacement of less than 50mm.2. Experiments on an artificial fracture showed that the permeability of the fracture varied by 7.5 to 11.5% and that the hydraulic aperture gradually decreased with an increase in both normal and shear stresses.3. Experiments on a tensile fracture showed that the experimental system could evaluate the permeability for a pore pressure of less than 0.3MPa, but a problem to be solved remained since air was trapped in the fracture.Main results obtained by theoretic … More al studies can be summarized as follows :1. A computer code for creating a synthetic fracture reproduced the ratio of the power spectral densities (PSDs) between aperture and surface height, measured for a tensile fracture of 1m in granite.2. The size effect on the permeability of a normally closed fracture disappears when the fracture exceeds 0.2m since the size effect on the standard deviation (SD) of the initial aperture disappears when the fracture size exceeds 0.2m. We proposed an empirical formula for the permeability of a normally closed fracture, which is independent of the fracture size and the SD of the aperture. Similarly, the size effect on the permeability of a sheared fracture disappears when the shear displacement is less than about 3.1% of the fracture size since the size effect on the standard deviation (SD) of the initial aperture disappears under such conditions.3. The anisotropy in the permeability of a sheared fracture increases with both shear displacement and closure. This anisotropy is caused by the difference in the aperture PSDs between two directions of macroscopic water flow ; perpendicular and parallel to the shear displacement. Furthermore, water flow is more localized with the shear displacement since a fewer channels with a greater area are formed as the shear displacement increases. Less

本研究对真三轴压缩条件下裂缝的渗透性进行了实验研究，并利用12.8m长的人工合成裂缝对裂缝的开度和渗透性进行了理论研究。本研究开发的实验系统可以在孔隙压力小于0.3MPa和剪切位移小于50 mm的均匀正应力下评估裂缝渗透率的非均匀性。人工裂缝实验表明，裂缝渗透率变化范围为7.5 ~ 11.5%，水力开度随正应力和剪应力的增加而逐渐减小.拉伸裂隙试验表明，该试验系统可以在孔隙压力小于0.3MPa的情况下评价裂隙的渗透性，但由于裂隙中存在空气，因此存在一个有待解决的问题 ...更多信息主要研究内容如下：1.用于创建合成裂缝的计算机代码再现了孔径和表面高度之间的功率谱密度（PSD）的比率，该比率是针对花岗岩中1米的拉伸裂缝测量的。当裂缝尺寸超过0.2m时，对常闭裂缝渗透率的尺寸效应消失，因为当裂缝尺寸超过0.2m时，对初始孔径标准差（SD）的尺寸效应消失。提出了一个常闭裂缝渗透率的经验公式，该公式与裂缝尺寸和孔径SD无关。同样，当剪切位移小于裂缝尺寸的3.1%时，裂缝渗透率的尺寸效应消失，因为在这种条件下，裂缝初始孔径的标准差（SD）的尺寸效应消失.剪切裂缝渗透率的各向异性随着剪切位移和闭合度的增加而增加。这种各向异性是由宏观水流的两个方向（垂直于剪切位移和平行于剪切位移）之间的孔径PSD差异引起的。此外，由于随着剪切位移的增加，形成更少的具有更大面积的通道，因此水流随着剪切位移而更加局部化。少