Importance

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Abstract

Methods of operation of different types of multiple electrode apparatus vertically disposed in a cased well to measure information related to the resistivity of adjacent geological formations from within the cased well are described. The multiple electrode apparatus has a minimum of two spaced apart voltage measurement electrodes that electrically engage a first portion of the interior of the cased well and that provide at least first voltage information. Current control means are used to control the magnitude of any selected current that flows along a second portion of the interior of the casing to be equal to a predetermined selected constant. The first portion of the interior of the cased well is spaced apart from the second portion of the interior of the cased well. The first voltage information and the predetermined selected constant value of any selected current flowing along the casing are used in part to determine a magnitude related to the formation resistivity adjacent to the first portion of the interior of the cased well. Methods and apparatus having a plurality of voltage measurement electrodes are disclosed that provide voltage related information in the presence of constant currents flowing along the casing which is used to provide formation resistivity.

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First Claim