Underground imaging by frequency‐domain electromagnetic migration

Zhdanov, Michael S.; Traynin, Peter; Booker, J. R.

doi:10.1190/1.1443995

Cited by 59 publications

(26 citation statements)

References 8 publications

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“…We have calculated the theoretical EM fields for these models using the code PW2D discussed by Wannamaker et al (1987). For numerical calculation of the migration field we use finite-difference code, developed in our paper (Zhdanov et al, 1996). Figure 1(a) depicts a locally conductive rectangular-insert 2-D model.…”

Section: Iterative Migrationmentioning

confidence: 99%

“…Solution of this problem is important for many practical applications ranging from mineral exploration to waste and building site characterization. In the papers (Zhdanov et al, 1995) and (Zhdanov et al, 1996) and the references therein we have developed a novel approach to EM imaging based on the notion of EM migration. The method includes downward continuation of the observed field or one of its components in reverse time and application of the corresponding imaging conditions.…”

Section: Introductionmentioning

confidence: 99%

“…The main problem is that the background conductivity distribution used for migration should be known a priori, while in the case of conventional inversion it is usually generated in the process of inverse problem solution. Different ways of solving this problem have been discussed in our paper (Zhdanov et at., 1996).…”

Section: Iterative Migrationmentioning

confidence: 99%

“…C. Farquharson and D. Avdeev, for their helpful remarks. Following our previous publications (Zhdanov and Keller, 1994;Zhdanov et al, 1996), we introduce the EM migration field as the solution of the boundary value problem for the ad- The last two equations give the integral representations for the solution of the boundary value problem for the migrated residual field.…”

Section: Iterative Migrationmentioning

confidence: 99%

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Migration versus Inversion in Electromagnetic Imaging Technique

Zhdanov

Traynin

1997

J. geomagn. geoelec

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One of the most challenging problems in electromagnetic (EM) geophysical methods is developing fast and stable methods of imaging inhomogeneous underground structures using EM data. In our previous publications we developed a novel approach to this problem, using EM migration.In this paper we demonstrate that there is a very close connection between the method of EM migration and the solution of the conventional EM inverse problem. Actually, we show that migration is an approximate inversion. It realizes the first iteration in the inversion algorithm, based on the minimization of the residual field energy flow through the profile of observations. This new theoretical result opens a way for formulating a new imaging condition. We compare this new imaging condition with the traditional one, obtained for simplified geoelectrical models of the subsurface structures.This result also leads to the construction of a solution of the inverse EM problem, based on iterative EM migration in the frequency domain, and gradient (or conjugate gradient) search for the optimal geoelectrical model. However, the authors have found that in the framework of this method, even the first iteration, based on the migration of the residual field, generates a reasonable geoelectrical image of the subsurface structure. IntroductionOne of the most challenging problems in electromagnetic (EM) geophysical methods is developing fast and stable methods of imaging inhomogeneous underground structures using EM data. Solution of this problem is important for many practical applications ranging from mineral exploration to waste and building site characterization. In the papers (Zhdanov et al., 1995) and (Zhdanov et al., 1996) and the references therein we have developed a novel approach to EM imaging based on the notion of EM migration. The method includes downward continuation of the observed field or one of its components in reverse time and application of the corresponding imaging conditions. However, until recently the relationship between EM migration imaging and traditional EM inversion have remained unexplored. The conventional EM inversion means a method which predicts the geoelectrical model generating the theoretical data closed to observations. The EM migration introduced in our previous publications constructed an image of subsurface geoelectrical structures, and there was no guarantee this image, if included in a geoelectrical model, would give rise to theoretical EM fields that matched those observed. Meanwhile, Tarantola (1987) demonstrated that seismic wave migration, which was the prototype for EM migration, can be treated exactly as the first iteration in some general wave inversion scheme. In this paper we formulate an important new result: EM migration, as the solution of the boundary value problem for the adjoint Maxwell's equation in frequency domain, can be clearly associated with the inverse problem solution. In other words, we prove that a geoelectrical model constructed on the basis of migration images would actually generat...

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Section: Iterative Migrationmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Iterative Migrationmentioning

confidence: 99%

Section: Iterative Migrationmentioning

confidence: 99%

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Migration versus Inversion in Electromagnetic Imaging Technique

Zhdanov

Traynin

1997

J. geomagn. geoelec

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“…The streamer system has the potential of reducing acquisition cost and providing denser receiver spacing. The dense receiver spacing is crucial for many techniques such as CSEM migration (Zhdanov et al, 1995(Zhdanov et al, , 1996Zhdanov and Traynin, 1997), up-down decomposition, and CSEM interferometry (Wapenaar et al, 2008;Fan et al, 2009;Hunziker et al, 2009Hunziker et al, , 2010. One drawback, however, is the bigger loss of energy in the sea water because the source and receiver are near the sea surface.…”

Section: Shallow Sources and Receiversmentioning

confidence: 99%

Increasing the sensitivity of controlled-source electromagnetics with synthetic aperture

et al. 2012

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Controlled-source electromagnetics (CSEM) has been used as a derisking tool in the hydrocarbon exploration industry. We apply the concept of synthetic aperture to the lowfrequency electromagnetic field in CSEM. Synthetic aperture sources have been used in radar imaging for many years. Using the synthetic aperture concept, big synthetic sources can be constructed by adding the response to small sources (building blocks) in different ways, and consequently, big sources with different radiation patterns can be created. We show that the detectability of hydrocarbons is significantly enhanced by applying synthetic aperture to CSEM data. More challenging targets such as deep reservoirs (4 km below sea floor) can be detected. The synthetic aperture technique also increases the sensitivity of the field to subsurface targets in the towing streamer acquisition. We also show that a pseudovertical source (orthogonally distributed dipole pairs) can be constructed synthetically, and that the detection capability of this pseudovertical source is increased by applying field steering. The synthetic aperture concept opens a new line of research in CSEM, with the freedom to design suitable synthetic aperture sources for a given purpose.

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Magnetotelluric tensors, electromagnetic field scattering and distortion in three‐dimensional environments

Brown

2016

JGR Solid Earth

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This paper describes how subsurface resistivity distributions can be estimated directly from the magnetotelluric (MT) tensor relationship between electric and magnetic fields observed on a three‐dimensional (3‐D) half‐space. It presents an inhomogeneous plane wave analogy where relationships between horizontal electric and magnetic fields, and an apparent current density define an apparent resistivity tensor constructed from a quadratic function of the MT tensor. An extended‐Born relationship allows the electric field to be normalized with respect to an apparent background current density. The model is generalized by including the vertical magnetic field in a 3 by 3 MT response tensor. A complex apparent wave number tensor, constructed from this tensor, has eigenvalues which, using the plane wave analogy, are the vertical wave numbers associated with the eigenpolarizations of propagating waves in the model half space. The elements associated with the vertical magnetic field transfer function define the horizontal wave numbers. An extended 3 by 3 phase tensor contains four elements of the conventional 2 by 2 phase tensor and two elements associated with the vertical magnetic transfer function. The extended phase tensor and a single real distortion tensor with six independent elements can be used to quantify static electric and magnetic field distortions. The approach provides a theoretical basis for visualization and migration of MT data, in comparison with results from other electrical and EM techniques, a starting point for constrained 3‐D inversions, and an assessment of results with other geophysical and geological data.

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Underground imaging by frequency‐domain electromagnetic migration

Cited by 59 publications

References 8 publications

Migration versus Inversion in Electromagnetic Imaging Technique

Migration versus Inversion in Electromagnetic Imaging Technique

Increasing the sensitivity of controlled-source electromagnetics with synthetic aperture

Magnetotelluric tensors, electromagnetic field scattering and distortion in three‐dimensional environments

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