Theoretical and practical considerations for crosswell electromagnetic tomography assuming a cylindrical geometry

Journal Article · Mon May 01 04:00:00 EDT 1995 · Geophysics

DOI:https://doi.org/10.1190/1.1443822· OSTI ID:87549

Alumbaugh, D L; Morrison, H F ^[1]

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1. Univ. of California, Berkeley, CA (United States)

An iterative Born imaging scheme is employed to analyze the resolution properties of crosswell electromagnetic tomography. The imaging scheme assumes a cylindrical symmetry about a vertical magnetic dipole source and employs approximate forward modeling at each iteration to update the internal electric fields. Estimation of the anomalous conductivity is accomplished through least-squares inversion. Much of the mathematical formation of this diffusion process appears similar to the analyses of wavefield solutions, but the attenuation implicit in the complex propagation constant invalidates many of the accepted wavefield criteria for resolution. Images of illustrative models show that vertical resolution improves with increasing frequency and with increased spatial sampling density. In addition, greater conductivity contrasts between the target and the background can result in better resolution. The horizontal resolution depends on the maximum aperture that is employed and with increasing frequency, larger apertures are needed to obtain optimal results. However, the maximum aperture that can be employed, and thus the horizontal resolution, is limited by the rate of attenuation and the noise present in the measurements. Weighting the long-offset data equally with the zero-offset data can improve the resolution if the noise is not a function of the dynamic range of the measurement system. At lower frequencies, the resolution can be improved by measuring both the horizontal and vertical components of the magnetic fields. In addition, multiple frequencies can be employed to improve the resolution for limited aperture measurements.

• DOE Contract Number: AC03-76SF00098; AC04-94AL85000
• OSTI ID: 87549
• Journal Information: Geophysics, Journal Name: Geophysics Journal Issue: 3 Vol. 60; ISSN GPYSA7; ISSN 0016-8033
• Country of Publication: United States
• Language: English

Related Subjects

02 PETROLEUM
03 NATURAL GAS
58 GEOSCIENCES
ATTENUATION
ELECTROMAGNETIC RADIATION
ELECTROMAGNETIC SURVEYS
GEOLOGIC DEPOSITS
IMAGE PROCESSING
ITERATIVE METHODS
MATHEMATICAL MODELS
RESOLUTION
RESPONSE FUNCTIONS
TOMOGRAPHY