Resistivity imaging of controlled‐source audiofrequency magnetotelluric data

Geophysics ◽  
1992 ◽  
Vol 57 (7) ◽  
pp. 952-955 ◽  
Author(s):  
Yutaka Sasaki ◽  
Yoshihiro Yoneda ◽  
Koichi Matsuo
Keyword(s):  
Current Loop ◽  
Magnetotelluric Data ◽  
Model Inversion ◽  
Controlled Source ◽  
Smooth Model ◽  
Resistivity Model ◽  
Em Method ◽  
Survey Results ◽  
Plane Wave Approximation ◽  
A Current

The controlled‐source audiofrequency magnetotelluric (CSAMT) method is an electromagnetic (EM) method where a transmitter (a grounded electric bipole or a current loop) is placed far away from the receiver sites. If the transmitter is located at distances greater than 3–5 skin depths, the plane-wave approximation is valid and the techniques used for (natural source) MT interpretation can be applied (Goldstein and Strangway, 1975; Sandberg and Hohmann, 1982). The CSAMT method can be employed in a detailed survey by closely spacing a number of receiver sites along a traverse. The borehole CSAMT technique is proposed in West and Ward (1988) to enhance the ability of the surface CSAMT method to detect subsurface inhomogeneities. In these cases, two‐dimensional (2-D) smooth‐model inversion (Rodi et al., 1984; Sasaki, 1989; deGroot‐Hedlin and Constable, 1990) would be particularly useful for deriving a resistivity model from the far‐field data and for presenting the survey results in the form of an image.

Seismic image-guided 3D inversion of marine controlled-source electromagnetic and magnetotelluric data

2020 ◽  
Vol 8 (4) ◽  
pp. SS1-SS13 ◽  
Author(s):  
Randall L. Mackie ◽  
Max A. Meju ◽  
Federico Miorelli ◽  
Roger V. Miller ◽  
Carsten Scholl ◽  
...  
Keyword(s):  
Structural Complexity ◽  
Structural Similarity ◽  
Hydrocarbon Exploration ◽  
Magnetotelluric Data ◽  
Controlled Source ◽  
Seismic Image ◽  
New Frontier ◽  
Gradient Fields ◽  
Resistivity Model ◽  
Geologic Interpretation

Geologic interpretation of resistivity models from marine controlled-source electromagnetic (CSEM) and magnetotelluric (MT) data for hydrocarbon exploration and reservoir monitoring can be problematic due to structural complexity and low-resistivity contrasts in sedimentary units typically found in new frontier areas. It is desirable to reconstruct 3D resistivity structures that are consistent with seismic images and geologic expectations of the subsurface to reduce uncertainty in the evaluation of petroleum ventures. Structural similarity is achieved by promoting a cross-gradient constraint between external seismically derived gradient fields and the inversion resistivity model. The gradient fields come from coherency weighted structure tensors computed directly from the seismic volume. Consequently, structural similarity is obtained without the requirement for any horizon interpretation or picking, thus significantly reducing the complexity and effort. We have determined the effectiveness of this approach using CSEM, MT, and seismic data from a structurally complex fold-thrust belt in offshore northwest Borneo.

Three-dimensional inversion of controlled-source audio-frequency magnetotelluric data based on unstructured finite-element method

2020 ◽  
Vol 17 (3) ◽  
pp. 349-360
Author(s):  
Xiang-Zhong Chen ◽  
Yun-He Liu ◽  
Chang-Chun Yin ◽  
Chang-Kai Qiu ◽  
Jie Zhang ◽  
...  
Keyword(s):  
Finite Element Method ◽  
Finite Element ◽  
Three Dimensional ◽  
Audio Frequency ◽  
Magnetotelluric Data ◽  
Controlled Source ◽  
Element Method

Deep electrical structure of northern Alberta (Canada): implications for diamond exploration

2009 ◽  
Vol 46 (2) ◽  
pp. 139-154 ◽  
Author(s):  
Erşan Türkoğlu ◽  
Martyn Unsworth ◽  
Dinu Pana
Keyword(s):  
Subduction Zone ◽  
Upper Mantle ◽  
Lithospheric Mantle ◽  
Three Dimensional ◽  
Diamond Formation ◽  
Magnetotelluric Data ◽  
Diamond Exploration ◽  
Upper Mantle Structure ◽  
Resistivity Model ◽  
Northern Alberta

Geophysical studies of upper mantle structure can provide constraints on diamond formation. Teleseismic and magnetotelluric data can be used in diamond exploration by mapping the depth of the lithosphere–asthenosphere boundary. Studies in the central Slave Craton and at Fort-à-la-Corne have detected conductors in the lithospheric mantle close to, or beneath, diamondiferous kimberlites. Graphite can potentially explain the enhanced conductivity and may imply the presence of diamonds at greater depth. Petrologic arguments suggest that the shallow lithospheric mantle may be too oxidized to contain graphite. Other diamond-bearing regions show no upper mantle conductor suggesting that the correlation with diamondiferous kimberlites is not universal. The Buffalo Head Hills in Alberta host diamondiferous kimberlites in a Proterozoic terrane and may have formed in a subduction zone setting. Long period magnetotelluric data were used to investigate the upper mantle resistivity structure of this region. Magnetotelluric (MT) data were recorded at 23 locations on a north–south profile extending from Fort Vermilion to Utikuma Lake and an east–west profile at 57.2°N. The data were combined with Lithoprobe MT data and inverted to produce a three-dimensional (3-D) resistivity model with the asthenosphere at 180–220 km depth. This model did not contain an upper mantle conductor beneath the Buffalo Head Hills kimberlites. The 3-D inversion exhibited an eastward dipping conductor in the crust beneath the Kiskatinaw terrane that could represent the fossil subduction zone that supplied the carbon for diamond formation. The low resistivity at crustal depths in this structure is likely due to graphite derived from subducted organic material.

Structure of the near zone of a current-loop antenna in a magnetoactive plasma

1988 ◽  
Vol 31 (4) ◽  
pp. 299-308 ◽  
Author(s):  
V. I. Karpman ◽  
A. I. Osin ◽  
O. F. Pogrebnyak
Keyword(s):  
Magnetoactive Plasma ◽  
Loop Antenna ◽  
Current Loop ◽  
Near Zone ◽  
A Current
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