原始电阻率各向异性岩石电阻率变化的方向性

DIRECTIONAL CHARACTERISTIC OF RESISTIVITY CHANGES IN ROCK OF ORIGINAL RESISTIVITY ANISOTROPY

在 3种非含岩成分造成的岩石原始电阻率各向异性标本 (在采集和加工过程中 ,标本完整性遭到破坏的标本 ) ,和一种由含岩成分形成的岩石原始电阻率各向异性标本上 ,布设多个电极 ,并将标本用水饱和 .然后用多电极组合法 ,将己布电极组合成不同方向、不同极距的电阻率各向异性测线 .采用单轴压缩、低围压三轴压缩和剪切3种加载方式 ,对标本进行动态电阻率变化实验 .观测标本电阻率随承载力的变化 .实验结果表明∶对于岩石原始电阻率各向异性标本 ,在电阻率变化各向异性方面 ,与岩石原始电阻率各向同性标本相似 ,即∶裂隙和破碎带通过区域的测点 ,视电阻率变化各向异性结果好 ,4种组合求得的 4个各向异性主轴方向趋向一致 ,且与破碎带方向基本吻合 ;裂隙和破碎带不经过区域的测点 ,4个视电阻率变化各向异性主轴方向不一致 ,或者根本求不出各向异性解 .这后一种情况 ,在裂隙面平行测量面时 ,表现最为明显 .

Multiple electrodes are arranged on the surfaces of samples, which include three kinds of resistivity of anisotropic samples not formed by ingredient of rock (The original resistivity anisotropy of the samples is due to the integrity of samples be damaged in the process of sampling and processing) and a kind of samples formed by ingredient of rock. The samples are fully saturated with water. The multiple electrodes are combined form arrays of resistivity changing anisotropy in different direction and spacing. The experiments of dynamic rock resistivity change are done with uniaxially compression, low confining pressure and shear. The variations of resistivity during the whole loading process are observed. The experimental results are the following: The samples of original resistivity anisotropy are essentially accordant with the samples of original resistivity isotropy in resistivity changing anisotropy. Namely, for the measuring-points located at cracks or rupture bands, the results of resistivity changing anisotropy are good, the four directions deduced from four kinds of combinatorial equation sets of resistivity are essentially identical with each other and approximately coincide with the orientation of cracks or main rupture bands; for the measuring-points without cracks or rupture bands passing through, the four directions calculated by different combinatorial arrays of resistivity are inconsistent with each other, or the direction can not be determined, especially in the cases when the crack plane is parallel to the measuring-surface.