A comparison of loop time-domain electromagnetic and short-offset transient electromagnetic methods for mapping water-enriched zones — A case history in Shaanxi, China

Geophysics ◽  
2017 ◽  
Vol 82 (6) ◽  
pp. B201-B208 ◽  
Author(s):  
Weiying Chen ◽  
Guoqiang Xue ◽  
Afolagboye Lekan Olatayo ◽  
Kang Chen ◽  
Muhammad Younis Khan ◽  
...  
Keyword(s):  
Time Domain ◽  
Mining Depth ◽  
Transient Electromagnetic ◽  
Resolution Capability ◽  
Electromagnetic Methods ◽  
Detection Depth ◽  
Reliable Detection ◽  
Time Domain Electromagnetic ◽  
Tem Method ◽  
And Inversion

Increases in the mining depth of coal pose a significant challenge to the conventional loop source time-domain electromagnetic (TEM) method that requires significant enlargement of the loop size and transmitting current to realize the deeper sounding results required. As an alternative, TEM devices based on a grounded wire source are generally used to solve detections deeper than several hundred meters. To map the water-enriched zones buried underneath approximately 1000 m at a coal mine in Shaanxi, China, loop TEM and short-offset transient electromagnetic (SOTEM) measurements were conducted. We carried out 1D forward modeling and inversion constrained by drilling informa-tion, and the results reveal that the resolution capability of loop TEM and SOTEM is almost the same in detecting a conductive layer in the absence of any noise. However, for a given noise level and decay time, the SOTEM method provides a deeper investigation than loop TEM without compromising sensitivity. The field examples validated the synthetic results. The loop TEM with dimensions of [Formula: see text] realized a maximum depth of 1000 m, whereas the reliable detection depth of 1500 m was achieved by using a 723 m long grounded wire source using the SOTEM method. Moreover, the labor required is significantly reduced, and the efficiency is dramatically raised using the SOTEM method. Our results predict that the SOTEM method should play a more important role in deep hydrogeophysical investigations.

The use and misuse of apparent resistivity in electromagnetic methods

Geophysics ◽  
1986 ◽  
Vol 51 (7) ◽  
pp. 1462-1471 ◽  
Author(s):  
Brian R. Spies ◽  
Dwight E. Eggers
Keyword(s):  
Apparent Resistivity ◽  
Early Time ◽  
Asymptotic Formulas ◽  
Voltage Response ◽  
Late Time ◽  
Induced Voltage ◽  
Resistivity Curve ◽  
Transient Electromagnetic ◽  
Electromagnetic Methods ◽  
Tem Method

Problems and misunderstandings arise with the concept of apparent resistivity when the analogy between an apparent resistivity computed from geophysical observations and the true resistivity structure of the subsurface is drawn too tightly. Several definitions of apparent resistivity are available for use in electromagnetic methods; however, those most commonly used do not always exhibit the best behavior. Many of the features of the apparent resistivity curve which have been interpreted as physically significant with one definition disappear when alternative definitions are used. It is misleading to compare the detection or resolution capabilities of different field systems or configurations solely on the basis of the apparent resistivity curve. For the in‐loop transient electromagnetic (TEM) method, apparent resistivity computed from the magnetic field response displays much better behavior than that computed from the induced voltage response. A comparison of “exact” and “asymptotic” formulas for the TEM method reveals that automated schemes for distinguishing early‐time and late‐time branches are at best tenuous, and those schemes are doomed to failure for a certain class of resistivity structures (e.g., the loop size is large compared to the layer thickness). For the magnetotelluric (MT) method, apparent resistivity curves defined from the real part of the impedance exhibit much better behavior than curves based on the conventional definition that uses the magnitude of the impedance. Results of using this new definition have characteristics similar to apparent resistivity obtained from time‐domain processing.

Three-dimensional transient electromagnetic inversion with optimal transport

2021 ◽  
Vol 0 (0) ◽  
Author(s):  
Xiaomeng Sun ◽  
Yanfei Wang ◽  
Xiao Yang ◽  
Yibo Wang
Keyword(s):  
Time Domain ◽  
3D Model ◽  
Optimal Transport ◽  
Three Dimensional ◽  
Experimental Tests ◽  
Transient Electromagnetic Method ◽  
Inversion Problem ◽  
Wasserstein Metric ◽  
Transient Electromagnetic ◽  
Time Domain Electromagnetic

Abstract 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.

Possibilities of electromagnetic methods in the investigations of talik under lake (numerical modeling)

2020 ◽  
Author(s):  
Alexandr N. Shein ◽  
◽  
Vladimir V. Olenchenko ◽  
Yaroslav K. Kamnev ◽  
◽  
...  
Keyword(s):  
Numerical Modeling ◽  
Field Station ◽  
Transient Electromagnetic ◽  
Electromagnetic Methods ◽  
Tem Method

The paper presents the results of numerical modeling of electroresistivity tomography (ERT) and transient electromagnetic (TEM) signals for the model of a freezing talik under khasyrei near the "Parisento" field station (Gydan peninsula). The inversion of ERT data results in artifacts that interpreted as an increase of the talik with depth. It is shown that TEM method is useable to determine the bottom of the talik and the base of the permafrost at a depth of 300 m with an accuracy of 10 m.

Applicability of frequency-domain and time-domain electromagnetic methods for mountain permafrost studies

2001 ◽  
Vol 12 (1) ◽  
pp. 39-52 ◽  
Author(s):  
Christian Hauck ◽  
Mauro Guglielmin ◽  
Ketil Isaksen ◽  
Daniel Vonder Mühll
Keyword(s):  
Frequency Domain ◽  
Time Domain ◽  
Electromagnetic Methods ◽  
Mountain Permafrost ◽  
Time Domain Electromagnetic

Direct inversion of time‐domain electromagnetic data

Geophysics ◽  
1987 ◽  
Vol 52 (10) ◽  
pp. 1431-1435 ◽  
Author(s):  
A. G. Nekut
Keyword(s):  
Least Squares ◽  
Time Domain ◽  
Time Derivative ◽  
Image Method ◽  
Simple Method ◽  
Geoelectric Section ◽  
Direct Inversion ◽  
Transient Electromagnetic ◽  
Time Domain Electromagnetic ◽  
Central Loop

This note describes a simple method for converting transient electromagnetic (EM) sounding data into profiles of conductivity versus depth, based on an approximate image representation for the decaying induced ground currents. The method can provide one‐dimensional (1-D) inversion for any kind of time‐domain EM sounding data; the discussion here is limited to the case of central‐loop sounding. In particular, I apply the inversion to some time‐derivative central‐loop sounding data and demonstrate that essentially the same interpretation of the geoelectric section is obtained with the simple image method as is obtained using traditional iterative least‐squares fitting to layered models. This simple inverse can be computed much more quickly than an iterative least‐squares inverse, making it possible to estimate the geoelectric section concomitant with data acquisition.

Electromagnetic mapping of saline contamination at an active brine pit

1996 ◽  
Vol 33 (2) ◽  
pp. 309-323 ◽  
Author(s):  
I J Ferguson ◽  
W J Taylor ◽  
K Schmigel
Keyword(s):  
Frequency Domain ◽  
Time Domain ◽  
Power Lines ◽  
Late Time ◽  
Signal Distortion ◽  
Electromagnetic Methods ◽  
Time Domain Electromagnetic ◽  
Survey Results ◽  
Limited Degree ◽  
Cultural Noise

Frequency-domain and time-domain electromagnetic methods were used to investigate groundwater contamination at an active brine pit in southwestern Manitoba, Canada. The objectives of the survey were to delineate contamination suspected to be occuring at the site and to compare frequency-domain electromagnetic (FDEM) and time-domain electromagnetic (TDEM) measurements in a survey area containing pipelines, fences, and power lines. The survey successfully delineated a region of high conductivity around brine pit, confirming that leakage is occurring from the pit. Modelling of the FDEM results suggests the contamination is spreading within a series of shallow sand units. Comparison of FDEM and TDEM survey results indicate that small-separation FDEM systems are much more useful for mapping in a developed area containing sources of cultural noise. The FDEM systems permit rapid mapping of spatial variations in conductivity, are affected to only a limited degree by cultural features, and provide some resolution of the depth variation of conductivity at shallow depth. It was not possible to obtain useful TDEM measurements anywhere near the active brine pit because of the signal distortion in the late-time response. Key words: geophysics, electromagnetic, brine pit, saline contamination.

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