Aftereffects in the Transient Electromagnetic Method: Inductively Induced Polarization

—Inductively induced electric polarization (IIP) is one of the aftereffects inherent in the geologic materials and affecting results of the transient electromagnetic method. Its effect on the inductive transient response manifests itself as a nonmonotonic EMF decay, including the polarity reversal. The dependence of IIP on many conditions makes it difficult to study the basic regularities in its manifestation. One of the ways to address this problem is to present the simulation results as a normalized transient response. From the most general point of view, the intensity and time range of the IIP manifestation are controlled by the competition between induction and induced polarization phenomena. Induced polarization manifests itself differently, depending on the transmitter used for the excitation of the ground response. Therefore, when studying polarizable ground, the results of the conventional IP method and those of the TEM method do not always correlate.

Research on Airborne Electromagnetic Whole-area Apparent Resistivity Imaging Algorithm in the Detection of Goaf in Rail Transit

Depth apparent resistivity imaging is an important process of data processing and analysis in the aviation transient electromagnetic method. It can provide reference value of conductor depth, vertical extension, and other information, and can accurately provide the measurement of each aviation transient electromagnetic measurement system. The structural section of the apparent conductivity of the one-dimensional layered medium on the line. As an advanced geophysical exploration technology, the aerial transient electromagnetic method has been applied significantly in the exploration of polymetallic minerals abroad in recent years. In this paper, based on the theory of ground-to-air transient electromagnetic method with multiple radiation sources, a corresponding multi-component global apparent resistivity definition method is established. The advantages of using the magnetic field strength to define the global apparent resistivity of the multi-radiation field source ground-air system are analysed. For each component of the magnetic field strength, respective global apparent resistivity algorithms are proposed to realize the multi-component, full-time, and full-space visual resistivity. The resistivity is calculated, and the influence of the offset on the global apparent resistivity is analysed. By adjusting the relative position of the source and the current direction and other parameters, the multi-radiation source transient electromagnetic ground-air system can not only strengthen the signal strength of different components, weaken random interference, but also better distinguish the location of underground anomalies

Research on application of mine transient electromagnetic method in detecting collapse column

The transient electromagnetic detection has been widely applied to mine roadway excavation engineering. In order to figure out the front geological conditions of roadway excavation, the application of mine transient electromagnetic method (TEM) in detecting collapse column was conducted in this paper by taking the TEM-based advanced detection of 53152 working face in a mine located in Jincheng, Shanxi Province as an example. The results showed that if TEM is applied, geological structures like water-free collapse column could be largely delineated. Besides, by combining the interference source of detection environment and related geological data nearby the detection site, ‘false abnormalities’ could be effectively eliminated, thus providing the reference basis for the water prevention and control work of mines.

Analysis of response characteristics of comprehensive geophysical prospecting technology in concealed water-bearing structures

The mine transient electromagnetic method and the mine direct current method were used to detect the abundant water at 1,144 m ahead of the track roadway on the 9101 working face in the Chaoyang Coal Mine. Low-resistance abnormal areas indicated by both methods were analyzed comprehensively for early warning of water hazards. The results showed that two low-resistance abnormal areas were indicated by the mine transient electromagnetic method and the existence of a low-resistance abnormal area was indicated by the direct current method. Both methods showed the existence of a low-resistance abnormal area ahead, delineating possible illegal mining areas of old kilns ahead, which were verified by drilling. The methods can indicate the direction for drilling. The case shows that the combination of different geophysical prospecting methods can eliminate their limitations and that comprehensive detection can reduce omissions, which has a good guiding significance for safe mine excavation.

Application of Comprehensive Geophysical Prospecting Method in Water Accumulation Exploration of Multilayer Goaf in Integrated Mine

A coal mine in Datong is an integrated mine. At present, there is goaf in the upper and lower part of the mining coal seam. There is a lot of ponding in the goaf, which has great potential safety hazards for production. In order to find out the scope and location of ponding in goaf, the comprehensive geophysical exploration method combining transient electromagnetic method and high-density resistivity method is used to carry out the research. Firstly, the time-base, turn-off time, receiving delay, current, superposition times, and other parameters of the instrument are tested on the surface of known goaf to obtain the best instrument parameters, and the parameters are used to verify the feasibility of the research scheme; then, the transient electromagnetic method is used for large-area exploration on the surface of the mine, the suspected goaf ponding area is found through comprehensive analysis, and the high-density resistivity exploration is arranged in the suspected goaf ponding area. According to the obtained results, the scope and location of the goaf ponding area are accurately located through comprehensive analysis. The results show that there are two goaf ponding areas in the exploration area, which are located above the 8# coal seam currently mined; the range and location of goaf ponding area can be accurately obtained by using the comprehensive geophysical method of high-density electrical method and transient electromagnetic method. This method can provide reference for mine water prevention and control in Datong area and has great practical significance to ensure coal mine safety production.

Three-dimensional transient electromagnetic inversion with optimal transport

Transient electromagnetic method (TEM), as one of the essential time-domain electromagnetic prospecting approaches, has the advantage of expedition, efficiency and convenience. In this paper, we study the transient electromagnetic inversion problem of different geological anomalies. First, Maxwell’s differential equations are discretized by the staggered finite-difference (FD) method; then we propose to solve the TEM inversion problem by minimizing the Wasserstein metric, which is related to the optimal transport (OT). Experimental tests based on the layered model and a 3D model are performed to demonstrate the feasibility of our proposed method.

Shallow velocity model from the transient electromagnetic method data: results of application in Eastern and Western Siberia

The geological section of Eastern and Western Siberia is an extremely complex object for a seismic exploration. The reason for this is the extremely high variability of the upper part of the section lithology, rough terrain, and permafrost rocks. This paper delivers an alternative approach to predicting the velocity model of the upper part of the section. The approach based on the original method of restoring the elastic-velocity characteristics from the data of transient electromagnetic method (TEM) in the near field zone. Research devoted to test the methodology of the shallow section velocity model calculation based on TEM data in a number of fields in Eastern and Western Siberia. Derived results aimed to improve the accuracy of the geological model building and the reliability of the hydrocarbon plays prediction. Synthetic modeling and field data confirm the high level of the proposed methodology effectiveness. It was shown that for the Eastern Siberia settings, an improvement in the quality of processing of seismic data consists in a significant increase in the dynamics and coherence of seismic recordings. In Western Siberia, it is possible to take into account the velocity anomalies associated with the permafrost rocks and zones of transit from the onshore part of the survey area to the sea. The main features of the study are useful in oil & gas companies and scientific institutions dealing with seismic data processing and interpretation to optimize expenses and improve blocks geology understanding.

The application of multi-grounded source transient electromagnetic method in the detections of coal seam goafs in Gansu Province, China

Unknown coal seam goafs will pose various safety hazards in construction and engineering designs, thus the accurate detections of coal seam goafs have become engineering problems that urgently require effective solutions. Multi-grounded source transient electromagnetic methods have the advantages of large detection depths and the easy deployment of emission sources. Therefore, they can be used for explorations in such complex areas as mountains, lakes and swamps. Previously, grounded source transient electromagnetic methods had only one emission source arranged on the surface, and were relatively rarely used in field explorations with multi-grounded sources. This study analyses the electromagnetic response differences between multi-grounded sources and a single-grounded source. The results reveal that the electromagnetic responses of multi-grounded sources were larger. Transient electromagnetic signals were be targeted using combinations of multi-grounded sources, which successfully strengthened the detection abilities. As a result, this study was able to achieve the goals of increasing the detection depths and improving the ability to distinguish geological anomalies. In addition, this research investigation referred to the theory of implicit functions and used the z components of the decay voltage to calculate the apparent resistivity. Finally, the results of the field data of a coal goaf located in Gansu Province, China, showed that the applied multi-grounded sources transient electromagnetic method could obtain higher resolution in coal seam goaf resistivity distribution information.