Imaging and Inversion of Transient Electromagnetic Soundings

1995 ◽  
Author(s):  
Niels B. Christensen
Keyword(s):  
Transient Electromagnetic ◽  
Electromagnetic Soundings ◽  
And Inversion

Full transmitter waveform transient electromagnetic modeling and inversion for soundings over coal measures

Geophysics ◽  
1987 ◽  
Vol 52 (3) ◽  
pp. 279-288 ◽  
Author(s):  
Michael W. Asten
Keyword(s):  
Case Depth ◽  
Earth Model ◽  
Electromagnetic Modeling ◽  
Resistive Layer ◽  
Homogeneous Half Space ◽  
Full Waveform ◽  
Transient Electromagnetic ◽  
Electromagnetic Soundings ◽  
And Inversion ◽  
Coal Measures

Modeling of transient electromagnetic soundings requires consideration of the full bipolar transmitter waveform in order to obtain full measurement accuracy from field instruments. The full‐waveform transient may be computed using existing impulse‐response forward algorithms followed by a convolution procedure with truncation and residual estimation after an even number of terms, which results in average increases in run time of about 80 percent. Simple calculations based on approximations for the behavior of transient decay over (a) a conductive layer over a resistive basement, (b) a homogeneous half‐space, and (c) a resistive layer over a conductive basement show that the effect of the full waveform is greatest at sample times near the end of the transmitter off‐time, and for the case of a conductive basement. Failure to consider the full waveform is expected to yield errors in the amplitude of the computed transient in the range of 4 to 100 percent or more, depending upon the sample time and type of earth model. Examples of soundings over moderately conductive coal measures and highly conductive cindered coal show that failure to use the full waveform yields depths and resistivities biased to erroneously high values. The bias is small in the former case, but produces substantial errors in the latter case. Depth to the electrical basement of 300 to 400 m may be estimated to accuracies of approximately 5 percent by computer inversion to three‐layer or four‐layer models.

Transient electromagnetic soundings

1982 ◽  
Author(s):  
Grigory Rozenberg ◽  
Pieter Hoekstra
Keyword(s):  
Transient Electromagnetic ◽  
Electromagnetic Soundings

1984 SEG Workshops Report of the special workshops presented December 6–7, 1984, following SEG’s 54th Annual International Meeting and Exposition in Atlanta

Geophysics ◽  
1985 ◽  
Vol 50 (7) ◽  
pp. 1183-1219
Keyword(s):  
Sedimentary Rocks ◽  
Acoustic Velocity ◽  
Seismic Exploration ◽  
Laboratory Measurements ◽  
International Meeting ◽  
Individual Basis ◽  
Transient Electromagnetic ◽  
Electromagnetic Soundings ◽  
Seismic Measurements

The workshop was organized into three topical units. The first unit included a presentation of laboratory measurements on a variety of frozen sedimentary rocks and permafrost, and an overview of problems and geophysical phenomena associated with permafrost. The second unit presented results of transient electromagnetic soundings in onshore and offshore permafrost environments. Comparisons were made with other geophysical results including acoustic velocity logs. Unit three of the workshop treated a variety of seismic measurements in diverse permafrost environments and served to focus the workshop on problems pertinent to seismic exploration for petroleum. This overview of the workshop was prepared by the organizers with review by the participants. Its purpose is to relate the principal topics and questions discussed in the workshop. Limitations on space require that greater detail on any topic be solicited on an individual basis from the appropriate participants.

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