Effect of Tool Eccentricity on Some Electrical Well-Logging Tools

John R. Lovell, Weng Cho Chew

Research output: Contribution to journalArticlepeer-review

Abstract

We present an algorithm to compute efficiently the propagation of nonaxially symmetric waves induced by realistic eccentered sources with a mandrel in a multicylindrically layered geometry. One of the applications of such a program is in electrical well logging, where oil exploration tools operate in a borehole drilled into the ground for geophysical subsurface sensing. The borehole surrounded by an invasion zone can be modeled as a multicylindrically layered geometry. We present an algorithm to study the effect of eccentricity (source and mandrel not in the center of the borehole) in the presence of concentric invasion zones around the borehole. The fields are decomposed into their spectral components by Fourier transforming along the z axis. For each such component, the boundary conditions between two concentric layers determines a system of 2 x 2 reflection and transmission matrices. These matrices, in turn, determine the ratio of “standing” waves to “outgoing” waves in each homogeneous region. This ratio is also a 2 x 2 matrix which can be calculated recursively [21]. Using the computed ratio for the center (borehole) region, an infinite system of equations is obtained which relates the geometry of the tool with a source, and a mandrel to that of the borehole and formation. The solution of this system of equations gives the amplitudes of the fields everywhere and, in particular, the signal measured by the receivers of the tool can be computed. We use our algorithm to study the eccentricity and invasion effects on an induction measurement and a dielectric logging measurement. In the case of dielectric logging, we find that the invasion zone may cause “resonance” effects, and that these effects remain when the tool is eccentered.

Original languageEnglish (US)
Pages (from-to)127-136
Number of pages10
JournalIEEE Transactions on Geoscience and Remote Sensing
Volume28
Issue number1
DOIs
StatePublished - Jan 1990

ASJC Scopus subject areas

  • Electrical and Electronic Engineering
  • Earth and Planetary Sciences(all)

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