ABSTRACT

Induction logs in sub-horizontal wells can provide important information about the properties of the formations. They help to characterize an invasion profile and determine the distances to the oil-water contact and remote beds. However, quantitative in-terpretation of induction data in a horizontal well, in a general case, requires three-dimensional modeling and analysis. Conventional, axial-coil, induction instruments face significant difficulties to accurately delineate formation and borehole geometry and conductivity anisotropy. In this paper we present a modeling study for a tensor instrument, comprising sets of three mutually orthogonal transmitting and receiving coils. We develop the theoretical solution based on generalized localized approximation. It realizes the 2.5-D algorithmic scheme, which efficiently models the concentric wellbore/invasion structures embedded in layered anisotropic formations. We examine the method's validity using analytical solutions for axially symmetric borehole and invasion models. We also analyze the compatibility of models for horizontal well situations with the models for highly deviated wells. The synthetic results demonstrate a very good match for dipping angles within a range of 90 + 15 degrees.

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