Three-dimensional massively parallel electromagnetic inversion-I. Theory

Newman, Gregory A.; Alumbaugh, David

doi:10.1111/j.1365-246x.1997.tb01559.x

Cited by 209 publications

(95 citation statements)

References 12 publications

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“…Newman and Alumbaugh, 1997). Yet, to our knowledge, no tomographic inversion results from mountain permafrost have been reported in the literature.…”

Section: Diffusive Electromagnetic Techniquesmentioning

confidence: 99%

Geophysical imaging of alpine rock glaciers

Maurer¹,

2007

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ABSTRACT. Slope instabilities caused by the disappearance of ice within alpine rock glaciers are an issue of increasing concern. Design of suitable counter-measures requires detailed knowledge of the internal structures of rock glaciers, which can be obtained using geophysical methods. We examine benefits and limitations of diffusive electromagnetics, geoelectrics, seismics and ground-penetrating radar (georadar) for determining the depth and lateral variability of the active layer, the distributions of ice and water, the occurrence of shear horizons and the bedrock topography. In particular, we highlight new developments in data acquisition and data analysis that allow 2-D or even 3-D structures within rock glaciers to be imaged. After describing peculiarities associated with acquiring appropriate geophysical datasets across rock glaciers and emphasizing the importance of state-of-the-art tomographic inversion algorithms, we demonstrate the applicability of 2-D imaging techniques using two case studies of rock glaciers in the eastern Swiss Alps. We present joint interpretations of geoelectric, seismic and georadar data, appropriately constrained by information extracted from boreholes. A key conclusion of our study is that the different geophysical images are largely complementary, with each image resolving a different suite of subsurface features. Based on our results, we propose a general template for the cost-effective and reliable geophysical characterization of mountain permafrost.

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“…Newman and Alumbaugh, 1997). Yet, to our knowledge, no tomographic inversion results from mountain permafrost have been reported in the literature.…”

Section: Diffusive Electromagnetic Techniquesmentioning

confidence: 99%

Geophysical imaging of alpine rock glaciers

Maurer¹,

2007

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“…Controlled Source electromagnetic (CSEM) prospecting has become an established tool for a wide range of exploration targets, including marine (Constable 2010), airborne (Siemon et al 2009) and cross well applications (Newman & Alumbaugh 1997). Despite all improvements during the last decade, the presence of steel-cased wells in the study area remains a challenging task for EM modelling methodologies.…”

Section: Introductionmentioning

confidence: 99%

Steel-cased wells in 3-D controlled source EM modelling

Patzer

Tietze²,

Ritter

2017

Geophysical Journal International

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S U M M A R YOver the last decades, electromagnetic methods have become an accepted tool for a wide range of geophysical exploration purposes and nowadays even for monitoring. Application to hydrocarbon monitoring, for example for enhanced oil recovery, is hampered by steelcased wells, which typically exist in large numbers in producing oil fields and which distort electromagnetic fields in the subsurface. Steel casings have complex geometries as they are very thin but vertically extended; moreover, the conductivity contrast of steel to natural materials is in the range of six orders of magnitude. It is therefore computationally prohibitively costly to include such structures directly into the modelling grid, even for finite element methods. To tackle the problem we developed a method to describe steel-cased wells as series of substitute dipole sources, which effectively interact with the primary field. The new approach cannot only handle a single steel-cased well, but also an arbitrary number, and their interaction with each other. We illustrate the metal casing effect with synthetic 3-D modelling of land-based controlled source electromagnetic data. Steel casings distort electromagnetic fields even for large borehole-transmitter distances above 2 km. The effect depends not only on the distance between casing and transmitter, but also on the orientation of the transmitter to the borehole. Finally, we demonstrate how the presence of steel-cased wells can be exploited to increase the sensitivity and enhance resolution in the target region. Our results show that it is at least advisable to consider the distribution of steel-cased wells already at the planning phase of a controlled source electromagnetic field campaign.

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“…The current state of the art in electromagnetic data inversion (Alumbaugh and Morrison [AM95a], [AM95b]) is based on the Born/Rytov approximation (requiring a low contrast assumption), even though it is known that conductivity variations range over several orders of magnitude and therefore require nonlinear analysis. Other work on inversion for this problem has been presented for example by Habashy et al [HGS93], Newman and Alumbaugh [NA97], and Haber et al [HAO00]. An alternative fully nonlinear approach to solving the EMIT imaging problem was introduced recently by Dorn et al [DBBP1,DBBP2].…”

Section: Introduction: Electromagnetic Imaging Of the Earthmentioning

confidence: 99%

Adjoint Fields and Sensitivities for 3D Electromagnetic Imaging in Isotropic and Anisotropic Media

Dorn

Bertete‐Aguirre

Papanicolaou

2008

Inverse Problems and Imaging

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Summary. In this paper we give an overview of a recently developed method for solving an inverse Maxwell problem in environmental and geophysical imaging. Our main focus is on low-frequency cross-borehole electromagnetic induction tomography (EMIT), although related problems arise also in other applications in nondestructive testing and medical imaging. In typical applications (e.g. in environmental remediation), the isotropic or anisotropic conductivity distribution in the earth needs to be reconstructed from surface-to-borehole electromagnetic data. Our method uses a backpropagation strategy (based on adjoint fields) for solving this inverse problem. The method works iteratively, and can be considered as a nonlinear generalization of the Algebraic Reconstruction Technique (ART) in x-ray tomography, or as a nonlinear Kaczmarz-type approach. We will also propose a new regularization scheme for this method which is based on a proper choice of the function spaces for the inversion. A detailed sensitivity analysis for this problem is given, and a set of numerically calculated sensitiviy functions for homogeneous isotropic media is presented.

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Three-dimensional massively parallel electromagnetic inversion-I. Theory

Cited by 209 publications

References 12 publications

Geophysical imaging of alpine rock glaciers

Geophysical imaging of alpine rock glaciers

Steel-cased wells in 3-D controlled source EM modelling

Adjoint Fields and Sensitivities for 3D Electromagnetic Imaging in Isotropic and Anisotropic Media

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