High resolution array induction tool

Abstract

A coil array for high resolution induction logging comprises a transmitter, a first receiver set positioned at a first distance from the transmitter and a second receiver set positioned at a second distance from the transmitter, and the second receiver set includes at least one portion of the first receiver set. Also disclosed is a method for deriving an apparent conductivity log from at least one induction well log that comprises a plurality of depth samples, comprising the steps of raising each depth sample of the apparent conductivity signal to several predetermined powers to generate a plurality of powers of conductivity, convolving in depth the powers of conductivity with a plurality of filters, where each power has a distinct filter, and summing the results of all of the convolutions to produce a conductivity log that is substantially free from the effects of adjacent beds and the nonlinear effects of true conductivity. Also disclosed is an apparatus for measuring the resistivity of an earth formation penetrated by a borehole, comprising at least one transmitter that is energized by a time-varying, periodic voltage, at least one set of receivers generating a receiver voltage, an analog-to-digital converter that periodically samples the receiver voltage at a predetermined sampling rate and outputs a digitized voltage signal, a processor that receives the digitized voltage signal, and a set of N accumulators that collates and averages successive sets of N samples from the analog-to-digital converters to output a set of N averages.