Application Of Transient Electromagnetic Method Research Articles

Study on the Coincident-Loop Transient Electromagnetic Method in Seafloor Exploration—Taking Jiaodong Polymetallic Mine as a Model

The transient electromagnetic (TEM) method becomes more urgent than ever for marine exploration due to abundant resource reserves and the increasing undersea engineering construction activities, especially in the offshore exploration of mineral deposits such as Sanshandao gold mine. However, the research and application of TEM method in marine environment are still challenged by many problems. Such contradiction motivates our study on the coincident-loop TEM in seafloor exploration. The TEM response of coincident loops is firstly derived in the integral form, based on the potential functions in Helmholtz equations for a magnetic source locating in the whole-space layered model. The frequency-domain vertical magnetic field is described as the Hankel integral with double first-order Bessel functions of first kind. Secondly, the time-domain induced voltage is obtained by transforming the frequency-domain response through the cosine transform and then taking the derivative of time. To simultaneously solve the Hankel transform and the cosine transform, a novel algorithm is introduced by adapting the fixed-point quadrature and extrapolation via the Shanks transformation. Finally, a typical conductivity model for marine polymetallic deposit is designed to investigate the characteristic of TEM response under various conditions. Numerical results demonstrate that existence of conductive seawater causes the TEM response to increase significantly and decay slower. The air-sea reflected electromagnetic waves lead to a significantly large fake negative response (NR) in shallower seawater with depth less than 300 m. Increase in the height of loops will weaken and delay the anomaly response and shorten the observation time-window. The height of configuration should be no more than 100 m for shallower targets and 50 m for deeper targets, respectively. The observation time-window should cover 10-1 000 ms. Increase in the radius of loops only enhances the TEM response proportionally but hardly improves the relative anomaly. The vertical resolution on the low-resistivity target approximates 20 m for the configuration considered in the study. Decreases in D.C. resistivity and chargeability cause the positive response (PR) to increase significantly and decay more rapidly. Meanwhile, the NR is advanced and enlarged significantly and decays slower compared with the PR. The influence of time constant is not monotony and there exists an optimal value for producing the maximum NR. As the frequency parameter increases, the PR is caused to decay more rapidly without magnitude change and the NR is advanced and decays more rapidly with significant increase in magnitude. The influence of frequency parameter is more pronounced than that of time constant.

瞬变电磁法在城市地下管线调查中的应用研究

瞬变电磁法在城市地下管线调查中的应用研究

Application of transient electromagnetic method (TEM) technique in South-East Asia: Case studies from onshore Sarawak and North Sumatra

Application of transient electromagnetic method (TEM) technique in South-East Asia: Case studies from onshore Sarawak and North Sumatra

Application of Transient Electromagnetic Method for Investigating the Water-Enriched Mined-Out Area

The water-enriched mined-out area, which led to frequent accidents and the serious destruction of ecological environment and serious threat to coal-mining practices. To ensure safe mining practices and to avoid the intrusion of water from the bases of coal deposits, the detection of the mined-out areas, especially the water-filled mined-out area in advanced, is one of the most important issues. This research focuses on detecting mined-out area enriched by water with the large-loop transient electromagnetic method. Data acquisition system was arranged along 23 survey lines, and the total of 1975 survey points were recorded. An inversion technique was used to interpret the TEM data. The inversion results suggested that the mined-out areas enriched by water always exhibit a very low-resistivity, the resistivity contour present closed circle sharp. There are three main water enriched mined-out areas, named JS1, JS2, and JS3 in the north part of the survey area, as well as three main water weak-enriched areas named RJS1, RJS2 and RJS3 in the west and southwest part of the survey area can be inferred by TEM, the interpretation results were verified by drilling. Large loop TEM is proved as an efficient way to investigate water enriched mined-out areas under the rugged topography conditions, and this work provides more detailed geological information to the coal mining enterprise for further coal-mining practices safety arrangement.

Double-transmitting and Sextuple-receiving Borehole Transient Electromagnetic Method and Experimental Study

With the continuous improvement of precision requirements for borehole geophysical exploration, the application of transient electromagnetic method (from now on referred to as TEM) in a borehole has become a hot spot. The conventional borehole TEM can only determine the longitudinal depth of the geological anomaly, the radial azimuth and depth cannot be resolved. A double-transmitting and sextuple-receiving borehole TEM is proposed, through which the radial anomaly is excited by the electromagnetic field generated by the double-emitting loops, and the azimuth and depth of the anomaly will be identified by the difference characteristics of the six receiving loops signals. In this paper, the response equations of the transmitting-receiving mode of double-transmitting and sextuple-receiving borehole TEM are deduced, and the response characteristics of the induction segment and the attenuation segment of the receiving loops are obtained based on the response equations under ramp function turn-off condition, providing the basis for theoretical analysis. Due to the negative value of the double-transmitting and sextuple-receiving transient electromagnetic response signals, a negative transformation algorithm under the double logarithmic coordinate system is proposed to provide the essential method for the analysis of two kinds of physical simulation experimental data of the radial azimuth and radial depth detection of the anomaly. The results show that the double-transmitting and sextuple-receiving borehole TEM has decent resolution ability in detecting the radial azimuth of the anomaly, and the effective resolution is 30°. The geometric difference among induced voltages of different measuring points can be used to evaluate the radial depth of the anomaly qualitatively. It is expected that the double-transmitting and sextuple-receiving borehole TEM can provide technical guidance for little borehole geophysical exploration in the fields of oil, natural gas, coal and basic engineering construction.

The Application of Transient Electromagnetic Method in Detecting the Corrosion of Heat Distribution Pipeline

Leakage of the heat distribution pipeline will seriously affect the safety of residents and cause economic losses. This paper presents the transient electromagnetic method (TEM) for detecting the corrosion of buried heat distribution pipeline, which mainly introduced the principle of the TEM to detect the pipeline and the general detection method. Combining with an instance of corrosion detection of buried heat distribution pipeline in a certain street in China Hohhot, the detection results were analyzed and the feasibility of this method was proved through excavation. The results show that the TEM can detect the uniform corrosion distribution of buried metal pipeline and it’s effective and practical for detecting the buried heat distribution pipeline. The TEM could provide a new method for guaranteeing the safe operation of the heat distribution pipeline.

Experimental Research on Transient Electromagnetic Multi-Turn Minor Loop Device

There is the polar distance selection of dipole device, the location determination of recording points, the resolution capability of multiple anomalies and other problems existing in the practical application of transient electromagnetic method in multi-turn minor loop device. Through physical simulation experiments, this paper gives experimental comparisons of polar distance, recording points, and the resolution capability of two anomalies in a certain interval between dipole device and overlapping device. The experimental results show that: the dipole device has the better resolution capability of small polar distance, 1.25 times wire-frame side length is appropriate for general selection of polar distance, and the maximum distance should not exceed 1.5 times wire-frame side length, the recording point is located in the midpoint position of transmitting and receiving coils; while the overlapping device has the obviously higher resolution of double anomalies in a certain interval than dipole device, and the minimum resolution is about 1.5 times wire-frame side length. These characteristics provide the realistic basis for reasonable selections and optimization designs of multi-turn minor loop observation system.

层状介质磁偶源瞬变电磁法正演及视电阻率计算<br>Forward Simulation and Apparent Resistivity Calculation of Transient Electromagnetic Method Using Magnetic Dipole Source on the Layered Medium

瞬变电磁法正演是进行多维瞬变电磁勘探理论研究的基础，通过正演计算可获得不同地电断面各场量瞬变耦合曲线，而中晚期场量均随着时间的增加迅速减小，将场量换算成视电阻率曲线，可获取地电断面的重要特征。本文首先导出层状介质磁偶源瞬变电磁法垂直磁场的计算公式及数值计算方法，建立典型的层状介质模型进行正演模拟，获得了磁场分量的衰减曲线，并将场量衰减曲线换算成视电阻率。计算结果表明视电阻率曲线直观的反映了地电断面特征，瞬变电磁法对低阻介质层的异常反应明显，同时场量误差分析表明正演结果可靠。 The forward of transient electromagnetic method (TEM) is the basis of the theoretical study of multi-dimen- sional transient electromagnetic prospecting. Transient coupling curves of each field component of different geoelectric sections can be obtained through forward calculation, and all the field components decrease rapidly as time increases in the middle and late time. Important characteristics of the geoelectric sections can be acquired by converting the field components to apparent resistivity curves. The calculation formula is derived from Hankel transform and G-S transform, and the numerical algorithm is proposed for the vertical magnetic field of transient electromagnetic method with mag- netic dipole source in the layered medium. Then the magnetic field components, calculated for several typical layered medium models, are converted to apparent resistivity values according to the definition of the apparent resistivity. The relative errors of the field components between the forward results and theoretical values are all less than 0.1%. The calculation results show that the apparent resistivity curves directly reflect the characteristics of geoelectric sections. And the anomaly of the low resistivity layer is more obvious than that of high resistivity layer. Furthermore, the negli- gible errors show that the forward results are reliable. It is valuable for theoretical research and practical application of transient electromagnetic method.

Effect of Application of Transient Electromagnetic Method in Detection of Water-Inrushing Structures in Coal Mines

Influenced by topographical and geological conditions, it is difficult for research of mine hydrological geophysics to rapidly and accurately detect passages inducing flooding of mines from water-accumulating abandoned mines, to detect precisely small structures causing flooding of mines. Through the study of the key technical difficult problems of the application of transient electromagnetic method(TEM) in hydrogeological exploration in coal mines, the characteristics of TEM such as sensibility to low resistivity, high transverse resolution and high speed have been sufficiently utilized. New inversion technologies have been used to improve the precision of TEM detection. During many rescues of water flooding induced by water inrush in coal mines, TEM has rapidly and accurately located water-inrushing structures in coal mines. It gains time for emergency rescue in coal mines, has significant social and economical benefits. TEM technology has become an important means for water control exploration in coal mines and has optimistic prospect of application.