Quasi-static transient response of a uniaxial conducting half-space /
Anisotropy in Earth materials often leads to unexpected geophysical responses that cannot be anticipated from simple isotropic models. In this study, I investigate the effect of lateral anisotropy on transient CSEM responses of a conducting half-space excited by a horizontal loop. This study invol...
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| Format: | Thesis Book |
| Language: | English |
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[Place of publication not identified] :
[publisher not identified] ;
2001.
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| Online Access: | http://proxy.library.tamu.edu/login?url=http://proquest.umi.com/pqdweb?did=726102511&sid=1&Fmt=2&clientId=2945&RQT=309&VName=PQD |
| Summary: | Anisotropy in Earth materials often leads to unexpected geophysical responses that cannot be anticipated from simple isotropic models. In this study, I investigate the effect of lateral anisotropy on transient CSEM responses of a conducting half-space excited by a horizontal loop. This study involves the mathematical solution, modeling, and interpretation of the behavior of the transient CSEM response. Mathematical solutions are derived which describe the behavior of current density components and the vertical component of magnetic field within the Earth. These are developed from Maxwell equations and boundary conditions to model the smoke ring in a uniaxial half-space. In this thesis, a pair of forward modeling computer programs have been developed to investigate the effect of fractures on the transient CSEM response. One program computes the theoretical response, as a function of time, of a horizontally anisotropic half-space to a sudden switch-off of electric current excited by a horizontal loop. The other program computes the elliptical diffusion smoke ring in a horizontally anisotropic half-space to a sudden step-on of electric current excited by the horizontal loop. Electromagnetic boundary value problems based on Maxwell's equations are solved analytically in the frequency domain. The vertical magnetic field component and the two horizontal current density components are then transformed into time domain by means of the Chave and Hanstein methods, respectively. Modeling elliptical diffusion smoke rings is done for two cases, namely [] (fractures more conductive than the matrix) and [] (fractures more resistive than the matrix). In the theoretical results, a "paradox of anisotropy" is observed in transient CSEM in which the field is more pronounced along the strike of relatively conductive fractures. This is opposite to what one might expect based on the isotropic theory. Smoke rings are discussed in this thesis. They take circular loops in a uniform isotropic half-space while they take an elliptical shape in a horizontally anisotropic half-space, diffusing downward and outward through the conducting medium. The transient behavior of the rings is characterized in detail. |
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| Item Description: | Vita. "Major Subject: Geophysics". |
| Physical Description: | xvi, 155 leaves : illustrations ; 28 cm. Issued also on microfiche from University Microfilm Inc. |
| Bibliography: | Includes bibliographical references (leaves 145-154). |