Relationship Between Detection Depth and Transmitting Frequency of Transient Electromagnetic Logging Instrument

2021 ◽  
pp. 204-216
Author(s):  
Bo Zhang ◽  
De-fu Zang ◽  
Shou-wei Zhang ◽  
Xi-wu Chen
Keyword(s):  
Transient Electromagnetic ◽  
Detection Depth

scholarly journals The study of imaging method for the moving controlled-source electromagnetic method

2019 ◽  
Vol 10 (2) ◽  
pp. 363-370
Author(s):  
Fengjiao Xu ◽  
Liangjun Yan ◽  
Osborne Kachaje
Keyword(s):  
Quantitative Relationship ◽  
Electromagnetic Method ◽  
Imaging Method ◽  
Oil Reservoir ◽  
Controlled Source ◽  
Transient Electromagnetic ◽  
Detection Depth ◽  
Resistivity Inversion ◽  
Oil Water ◽  
Set Up

Abstract Improving the accuracy and enhancing the reliability of controlled-source electromagnetic (CSEM) inversion in oil exploration in order to identify the interface between oil and water is a great challenge. In this paper, we proposed a variable-angle geometry imaging method by moving the source of CSEM (MCSEM). Firstly, based on the concept of multi-channel transient electromagnetic method, we obtained the quantitative relationship between the offset and detection depth, and then the geometry imaging principle of MCSEM was set up. Secondly, the feasibility study of the geometry imaging method was tested through the 1-D and 3-D forward modeling. Finally, by analyzing the collected field data of MCSEM method in Daqing oil reservoir, high-accuracy pseudo-apparent resistivity profile was obtained based on the geometry imaging method with the help of well-logging calibration. The results showed good compatibility with the 2-D TEM resistivity inversion which demonstrates that the MCSEM has great prospect potential in the identification of oil–water interface explorations.

Robust statistical methods for reducing sferics noise contaminating transient electromagnetic measurements

Geophysics ◽  
1996 ◽  
Vol 61 (6) ◽  
pp. 1633-1646 ◽  
Author(s):  
G. Buselli ◽  
Murray Cameron
Keyword(s):  
Transient Response ◽  
Background Noise ◽  
High Amplitude ◽  
Geological Mapping ◽  
Recursive Algorithms ◽  
Robust Estimate ◽  
Transient Electromagnetic ◽  
Detection Depth ◽  
Noise Data ◽  
The Mean

The transient electromagnetic (TEM) method is used extensively for mineral exploration and other applications such as geothermal soundings, oil exploration, groundwater pollution, soil salinity and geological mapping. Sferics pulses produced by lightning strokes propagating in the ionosphere‐earth waveguide cavity induce noise in a bandwidth of a few Hz to tens of kHz. The usual method of stacking and calculating the mean of a given stack cannot effectively reduce the spike‐like noise induced by high‐amplitude sferics pulses. To reduce this type of noise, a number of different ways of stacking data were investigated and compared. Noise data were stacked by using robust estimators such as the median, trimmed mean, and a range of M‐estimators. Since storage of all the samples of a given stack can take up a prohibitively large amount of microprocessor memory, recursive algorithms for the M‐estimators and their standard error were developed for the real‐time reduction of sferics pulses. The recursive algorithms have been demonstrated to work effectively on windowed data, and thus the memory normally required to obtain the mean is sufficient for calculation of the M‐estimate. In the recursive calculation of the robust estimate of the transient response, the spread of the background noise distribution (known as the scale of the data) needs to be known or calculated. In the algorithm that has been developed, the scale of the data is derived from a noise run carried out before pulsing the transmitter loop with current. It has been assumed that the presence of a signal does not change the scale of the data. This value of the scale of the data has been used to obtain a robust estimate of the transient response itself. To allow for possible changes in the background noise level during a given survey, the estimate of the scale of the data is updated throughout the survey. Many tests of the performance of the recursive algorithms have been carried out with both simulated noise data and sferics data that have been recorded previously on magnetic tape. The results show that for sferics activity as high as that observed in northern latitudes of Australia in summer, a noise reduction by a factor of about 5 (when compared with simple stacking) should be obtained. In areas where sferics noise predominates over geological background signal, such a reduction should lead to an increase in target detection depth by approximately 50%.

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.

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