Abstract

This theoretical investigation presents the responses in dipping beds of an induction dipmeter and standard induction tools, neglecting the influence of the borehole and invaded zones as well as the mandrel and coil size. The analysis is sufficiently general to determine response characteristics of an induction coil arbitrarily oriented in an arbitrary number of beds.In an induction dipmeter log (IDL) the most useful information is obtained from the out-of-phase voltage induced in the receiver coils when they are orthogonally oriented to the transmitter coils. A simple algorithm is developed to convert the crosscoupling signals into the apparent dip and strike information. The agreement between the actual and apparent values is nearly perfect for small transmitter-to-receiver spacings, i.e., less than 10 cm.The theoretical results for standard induction tools were consistent with prior work indicating the influence of dip is strongly dependent on the shoulder effect of the device in question. Consequently, dipping beds have less influence on the standard ILm because its shoulder effect is less than the standard ILd. These conclusions are supported by numerous simulations consistent with conditions encountered in the field.Finally, a simple no-skin-effect theory is developed for the case of a single dipping interface separating two infinitely thick beds. The results with this approach agree with the exact theory in resistive formations. This simplified theory is a generalization of Doll's geometrical factor theory.

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