Effect of tool eccentricity on some electrical well-logging tools

Abstract

An algorithm is presented 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 all 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. The authors also 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 authors' algorithm is used to study the eccentricity and invasion effects on an induction measurement and a dielectirc logging measurement. In the case of dielectric logging, they find that the invasion zone can cause resonance effects, and that these effects remain when the tool is eccentered.