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

本研究既进行了真三轴压缩下裂缝渗透率的实验研究，又利用长达12.8m的大型合成裂缝进行了裂缝孔径和渗透率的理论研究。实验研究的主要结果可总结如下： 1. 本研究开发的实验系统可以评价均匀正应力、孔隙压力小于0.3MPa、剪切位移小于50mm。2．人工裂缝实验表明，裂缝渗透率变化7.5%～11.5%，水力孔径随着法向应力和剪应力的增加而逐渐减小。3．系统可以评估孔隙压力小于0.3MPa的渗透率，但由于裂缝中存在空气，因此仍然存在一个有待解决的问题。理论研究获得的主要结果... 更多总结如下： 1. 用于创建合成裂缝的计算机代码再现了孔径与表面高度之间的功率谱密度（PSD）之比，在花岗岩中测量了 1m 的拉伸裂缝。 2. 尺寸对渗透率的影响。当裂缝超过 0.2m 时，常闭裂缝的特征消失，因为当裂缝尺寸超过 0.2m 时，初始孔径标准差 (SD) 的尺寸效应消失。常闭裂缝渗透率的经验公式，与裂缝尺寸和孔径的 SD 无关，同样，当剪切位移小于 3.1% 时，剪切裂缝渗透率的尺寸效应消失。裂缝尺寸，因为在这种条件下，初始孔径标准差（SD）的尺寸效应消失了。3．剪切裂缝渗透率的各向异性随着剪切位移和闭合而增加。各向异性是由垂直和平行于剪切位移的两个方向之间的孔径PSD的差异引起的。此外，由于剪切时形成的通道更少，面积更大，因此水流更加局域化。位移增加。