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Analysis of electromagnetic well-logging tools
Hue, Yik-Kiong

2006, Doctor of Philosophy, Ohio State University, Electrical Engineering.
This dissertation presents numerical and pseudoanalytical modeling techniques for the analysis of electromagnetic well logging tools in complex geophysical formations. The well-logging tools modeled here include measurement-while-drilling/logging-while-drilling (MWD/LWD) tools employing horizontal coil and for tilted-coil antenna arrays. The electromagnetic response of such tools are studied in cylindrical layered formations, including eccentric borehole, dipping bed layers, and/or anisotropic conductivities. The three main techniques used for modeling are the finite-difference time-domain (FDTD), a pseudoanalytical method, and numerical mode-matching. The FDTD method is implemented three-dimensional (3-D) cylindrical coordinates to handle arbitrary 3-D complex formations. The FDTD method developed here incorporates the following extensions: (i) A perfectly matched layer (PML) absorbing boundary condition in cylindrical coordinates to mimic open region problems, (ii) an efficient frequency domain data extraction technique to yield frequency domain data from early time domain data, (iii) two locally-conformal FDTD (LC-FDTD) techniques to model eccentric boreholes, and (iv) a scaling permittivity technique to overcome the Courant stability limit at the low frequency range. To provide validation results and a faster solution method in simpler formations, including multiple asymmetric cylindrical layered formations with eccentric boreholes, a pseudoanalytical method is also developed. This method is based on a decomposition of the solution into spectral components and on the use of the addition theorem for cylindrical waves to tackle eccentric borehole problems. Finally, a NMM method is developed and employed to model tilt-coil antenna array in multilayered anisotropic formations. The present NMM is based on an expansion of the field components in terms of vertical eigenmodes, and incorporates a PML in the vertical direction. B-splines are used to expand the fields in the vertical direction and cylindrical Bessel/Hankel functions are used for the radial dependency. The results from each method are validated against each other, showing very good agreement.
Fernando Teixeira (Advisor)

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