Directional Characteristics of Resistivity Changes in Rock of Original Resistivity Anisotropy

Abstract

According to pre-designed patterns, multiple electrodes are arranged on the surfaces of four samples. Among them three samples have the original resistivity anisotropy which was not formed by ingredient of rock and one sample has that 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 directions and spacing. The experiments of dynamic rock resistivity change are done with uniaxial compression, low confining triaxial compression and shear, and the variation of resistivity during the whole loading process is observed. The experimental results show that the samples of original resistivity anisotropy are essentially accordant with that of original resistivity isotropy in resistivity changing anisotropy. Namely, for the measuring-points that are 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 coincide with the orientations of cracks or main rupture bands approximately. For the measuring-points without cracks or rupture bands passing through, either 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 case that the crack plane is parallel to the measuring-surface.Key words Electrical resistivity of rock, Geoelectric resistivity, Anisotropy of rock resistivity, Main fracture of rock.

Experimental Studies on the Changes in Resistivity and Its Anisotropy Using Electrical Resistivity Tomography

“…For example, Mao et al [7,8] used the resistivity data measured along E-W and N-S trending measuring lines in studying the changes in the degree of earth resistivity anisotropy during the course of earthquake preparation. Chen et al [22][23][24][25] designed four measuring lines in studying the changes of apparent resistivity anisotropy in lab. In this paper, we arranged three measuring lines intersecting at point O (Figure 1), which allowed us to study the changes in apparent resistivity anisotropy at point O with pressure and depth.…”

“…The striking changes in electrical resistivity and its anisotropy were widely observed before earthquake, mine earthquake, volcanic activities, and geologic motions [1][2][3][4][5][6][7][8][9][10][11][12]. In order to address the change characteristics of resistivity and its anisotropy, many investigators conducted a plenty of experiments on rock samples under compression and during fracture, shear, and frictional sliding in lab [13][14][15][16][17][18][19][20][21][22][23][24][25] and theoretic studies [26][27][28][29][30]. Experimental results reported by Brace et al [13] and Brace and Orange [14][15][16] in lab showed that striking changes in electrical resistivity were observed for a variety of igneous and sedimentary crystalline rocks when water-saturated crystalline rocks were stressed to fracture.…”

“…Considering the effects of groundwater, An et al studied the changes in resistivity and its anisotropy with pressure in the presence of feed water [34]. In order to recognize the expansion of fissure with stress, Chen et al [22][23][24][25] studied the water-saturated granite samples and man-made samples under uniaxial compression, triaxial compression with low confining pressure, and frictional sliding. This previous work played very important role in recognizing and understanding the change behaviors of resistivity and its anisotropy with pressure, but they had to analyze the curves of resistivity and its anisotropy with pressure because of only a few electrodes designed on one measuring line.…”

Experimental Study on Conductivity Anisotropy of Limestone Considering the Bedding Directional Effect in the Whole Process of Uniaxial Compression

“…Based on the studies of Chen et al [ 12 ], Chen et al [ 15 , 16 , 17 , 18 ] gradually developed and improved the method of determining the main rupture direction of rock by using the anisotropy of the changes of the rock electrical resistivity. They performed a series of experimental studies on the anisotropy of the electrical resistivity of rock samples in uniaxial, low-confining-pressure triaxial and shear conditions by means of combined measurement of the anisotropy of the apparent resistivity, electrical profiling and electrical sounding.…”

Experimental study of the effect of thermal damage on resistivity and mechanical properties of sandstone

“…apparent resistivity of rock during the loading process was widely studied (Chen et al, 1987;Mao et al, 1988;Chen et al, 2003;Liao et al, 2003 analyzed the relationship between the anisotropy of the variation of dynamic rock resistivity and the change of water network conductive path caused by the extension of rock fracture through laboratory experiments, and then proposed a quantitative method of identifying the extending premonition of hidden fracture; the variation of the resistivity of water-saturated rock under uniaxial compression was studied (Brace, 1975), and the results showed that under 1/3 to 2/3 of the burst pressure during the loading process, the resistivity of saturated rock initially increased and then decreased rapidly.…”