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The Theoretical and Experimental Research on Self-Potential Tomography

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Abstract

In order to reveal the physical mechanism of self-potential (SP) anomaly, the theoretical method of SP tomography based on a semi-infinite space proposed by Patella was extended to a finite boundary condition. With the observational data from a quadrangle, the 2-D tomography of charge occurrence probability is reconstructed. A cuboid sample with square section has been studied through several numerical modeling and experimental investigations, and the charge occurrence and variation with crack extension was revealed clearly. It is found that the position of positive charges with a high probability coincides with the places of fractures in rock sample. It reflects a microscopic process of separation of positive and negative charges at the fracture ends. Thus SP tomography is helpful to deeply understand the physical mechanism of electric field changes during the fracture of rock.

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... The abnormal time series response characteristics of EPs can be regarded as a precursor of coal failure under the stress-gas coupling effect (Li et al. 2019a); the spatial distribution law of EPs enables to reveal the initiation and development process of local damages in coal (Li et al. 2019b). The inversion imaging method can reliably explore and analyze the spatial distribution law of the EP field based on EP data (Long and Hao 2005). ...
... The study results provide a new and valuable engineering application method for finely identifying outburst hazard and preventing and controlling the dynamic disasters in deep mines. EP monitoring shows its unique advantages compared to the traditional monitoring method for coal and gas outburst (Li et al. 2019a(Li et al. , b, 2020aLong and Hao 2005). (1) EP signals are not only sensitive to large-scale fracture events but also to the little-scale deformation inside the coal mass. ...
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Coal remains an important fuel and energy, especially in China. For coal mining in deep mines, the threat of coal and rock dynamic disasters (such as coal and gas outburst) to safe production is becoming more and more serious with the greatly increasing geo-stress and gas pressure. Hence, it is particularly important to real-timely monitor and finely identify outburst-hazardous zones and their hazard levels during coal mining. However, conventional methods fail to continuously and precisely monitor outburst-hazardous zones in spatial distribution. Previous studies have shown that under the coupling action of stress and gas, the electric potential (EP) signals can be generated and their response characteristics are closely related to the loading state and damage evolution process of coal. The inversion imaging method can be utilized to analyze the spatial distribution of the EP signals. On this basis, the field tests were conducted to study the EP response characteristics to the mining process of deep coal seams and analyze the relationship between the EP response and outburst hazard. Moreover, in view of the EP inversion imaging mechanism, the bilateral EP inversion n model was established on the mining-disturbed coal seam ahead of the mining face and the field application was also carried out. Furthermore, on account of the membership index of fuzzy mathematics, the critical EP inversion value was proposed. Then the outburst-hazardous zones in the coal seam ahead of the mining face were divided finely and identified quantitatively. In the end, the verification result showed that the yellow zones enable to identify most of outburst-hazardous zones, thus effectively avoiding the missing identification. Besides, the red zones can improve the identification efficiency, which is conducive to focusing on identifying zones with a high hazard level. The study results provide a valuable new application method for finely identifying coal and gas outburst hazards and preventing coal and rock dynamic disasters in deep coal mines.
... Coal mass damage and fracture can be regarded as the point source for abnormal charges, and produces EP signals on the boundary of EP measuring lines. The cloud map for distribution of charge sources in the coal can be obtained by computed tomography through inversion, using geophysical methods based on EP signals on the boundary of measuring lines [38]. This indirectly reveals the spatial distribution of EP signals. ...
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Across the world, coal resource is widely utilized in industrial production. During coal mining activities, dynamic disasters may be induced, such as coal and gas outbursts, or rock burst, resulting in serious accidents or disasters. Previous studies have shown that electric potential (EP) signals can be produced during the deformation and fracture process of coal and rock mass under load. The abnormal response characteristics of EP can reveal the damage evolution and failure feather of coal mass. In this paper, the response characteristics of EP signals are analyzed with high gas testing during mining activities within deep coal seams, and the relationship between the EP response and outburst disaster hazard is studied. The results show that: (1) Under the comprehensive action of mining stress and gas effect, the coal mass was damaged and fractured, which can produce abundant EP signals, while the temporal EP response characteristics can reflect the loading state and damage evolution process inside the coal seam. (2) When coal cannon and a sudden increase of gas concentration occurred in the coal mass, the EP signal was at a high level and fluctuated violently. This can be regarded as precursory information for an outburst risk, which was verified by monitoring the results of mining stress and electromagnetic radiation (EMR). (3) Based on the unilateral inversion imaging method, EP spatial distribution law was studied and abnormal zones with high-value were identified. The zone is close to, or coincident with, the high value interval of EMR intensity and count indexes, which revealed the distribution characteristics of coal damage localization. Hence, EP monitoring results can forecast precursor information of outburst hazards temporally, and identify local zones with outburst hazard spatially. This study provides a new idea and application basis for using the EP method to monitor and prevent coal and rock dynamic disaster hazards in the field.
... The rupture process of rock under pressure is evaluated by Long et al [11]. The generation process and distribution of self-potential in the process of microfracture extension are investigated. ...
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The relationship between ξ potential of near surface of rock and rock-breaking efficiency in recent years were reviewed. Based on the microscale of crystal lattice, the influence of cataclysmic change of induced dipole on ξ potential of near surface of rock core in the process of rock failure was investigated. The effect of changing potential on the hardness of near surface of rock was analyzed. The results indicated that ξ potential of near surface of rock could be changed suddenly by induced dipole from the crystal lattice of rock core caused by microfracture extension. In addition, the rock-breaking efficiency could be improved by changing ξ potential of rock surface. This study can be helpful for the design of novel additives for drilling fluids, and endow with economically and technically viable petroleum development and production processes.
... Applications in geohydrology concern the forced movement of water associated with deformation of porous rocks [e.g., Lorne et al., 1999aLorne et al., , 1999b Revil et al., 2003], the determination of preferential flow paths over karstic areas [Jardani et al., 2006a[Jardani et al., , 2006b, the determination of transmissive properties of unconfined aquifers [Titov et al., 2000], the determination of subglacial flow patterns [Kulessa et al., 2003a[Kulessa et al., , 2003b , CO 2 seques- tration [Moore et al., 2004], and the detection of leakages in embankments and dams and the interpretation of the resulting self-potential signals in terms of seepage velocity [e.g., Bogoslovsky and Ogilvy, 1970; Gex, 1980; Panthulu et al., 2001; Sheffer, 2002; Sheffer and Howie, 2001, 2003; Titov et al., 2005; Rozycki et al., 2006]. These works have also recently driven the development of new algorithms of selfpotential tomography [e.g., Long and Hao, 2005; Minsley et al., 2007] and tank-scale laboratory measurements in well-controlled conditions to check the underlying physics of these processes [Maineult et al., 2006a[Maineult et al., , 2006b Moore and Glaser, 2007]. Similar types of analysis were carried out recently in medical imaging to study the flow of electrolytes in cartilage submitted to mechanical loads [Sachs and Grodzinsky, 1995; Garon et al., 2002] and in plant sciences to monitor the flow of sap in trees [Gibert et al., 2006]. ...
... interpretation of the resulting self-potential signals in terms of seepage velocity [e.g., Bogoslovsky and Ogilvy, 1970; Gex, 1980; Panthulu et al., 2001; Sheffer, 2002; Sheffer and Howie, 2001, 2003; Titov et al., 2005; Rozycki et al., 2006]. These works have also recently driven the development of new algorithms of selfpotential tomography [e.g., Long and Hao, 2005; Minsley et al., 2007] and tank-scale laboratory measurements in well-controlled conditions to check the underlying physics of these processes [Maineult et al., 2006a [Maineult et al., , 2006b Moore and Glaser, 2007]. Similar types of analysis were carried out recently in medical imaging to study the flow of electrolytes in cartilage sub ...
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This paper is an extension of a previous study, in which the principles of self-potential ground surface tomography were outlined. The new arguments which are here set forth are the proper accounting for the topographic effects and a robust approach to global 3D tomography. The 2D case is initially considered in order to facilitate a full understanding of the new method. In order to gauge the topographic distortions, the concepts of slope effect and surface regularization are introduced, as suitable means to compute point by point correction factors of the measured self-potential data, prior to the recognition of the tomographic images of the primary and induced electric sources underground. The tomographic approach is then developed by introducing again the concepts of the scanning function and of the charge occurrence probability function, which were amply dealt with in the previous paper. The new approach to 3D global tomography means here the composition of charge occurrence probability functions related to any two orthogonal surface components of the natural electric field, in order to account fully for the total surface component of the self-potential field and hence to elicit the greatest amount of information. Two field examples are presented to show the full effectiveness of the proposed method. They refer, respectively, to a near-surface investigation for archaeological purposes and to a very deep investigation in an active volcanic area.
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The anomalies of electric-magnetic field and self-potential before earthquakes are important precursory phenomena. A simulating experiment study on the variations in ultra-low frequency (ULF) magnetic field and self-potential during rock cracking was carried out in a magnetic field-free space. The results revealing in detail the whole process of the occurrences of electric and magnetic anomalies are significant for understanding the microscopic mechanism of ULF electric and magnetic signals. The experiment indicated that at the initial stage the slow changes in strain, self-potential and magnetic field with small amounts appeared firstly near the source of initial cracking, and then extended as the crack developed on. In the time domain, the self-potential anomaly emerged first and ULF magnetic field changes arose then. The shape of the ULF electric and magnetic anomaly varied obviously in early-, mid- and late-term of the test. The authors attributed the pulse-like changes of self-potential to the generation and movement of the accumulated electric charges during the cracking caused by charge separation on the crack tips within the sample. While the magnetic pulses of shorter-period at the last stage of the test, may be induced by instantaneous electric current of the accumulated charge during the cracking acceleration. The technical method and the observational results of this experiment are given in detail and the microscopic mechanism of electric and magnetic precursors before earthquake are discussed in the present paper as well.
Article
The latest aspects of the physical properties of seismic electric signals (SES) that are used for earthquake prediction in Greece are described. The procedure currently followed for the selection of a site appropriate for the collection of SES and for the electric dipole configuration of such a station are reviewed. The process of constructing a map indicating the seismic areas for which such a station is sensitive is also described. A review of other electrical precursors observed in Greece is given, along with a summary of the newest theoretical models of the generation of SES. The compatibility of these models with the existing data on SES is discussed. Furthermore, a number of unsolved problems are listed, along with suggestions for future experimentation.
The evaluation of the probability imaging technology for natural electric field
  • Xu
The study of self-potential abnormity during the rock breaking Beijing Institute of Geophysics, China Earthquake Administration
  • H Long
Electron emission during rock fracture
  • Guo