Methods of operation of different types of multiple electrode apparatus vertically disposed in a cased well to measure information useful to determine the resistivity of adjacent geological formations from within the cased well are described. The multiple electrode apparatus has a plurality of spaced apart voltage measurement electrodes that electrically engage a portion of the interior of the cased well. During measurements of information useful to determine formation resistivity, current is conducted between a first current conducting electrode in electrical contact with the interior of the cased well to a second current conducting electrode that is also in electrical contact with the interior of the cased well. The first and second current conducting electrodes are separated by a distance sufficient so that at least a portion of the current conducted between the first and second current conducting electrodes is conducted through the geological formation of interest.
This invention was made with Government support under DOE Grant No. DE-FG06-84ER13294, entitled "Validating the Paramagnetic Logging Effect", Office of Basic Energy Sciences, of the U.S. Department of Energy. The government has certain rights in this invention. The basic concept for the invention described herein was conceived during the funding provided by the above grant.
Ongoing research to measure resistivity through casing has been provided on a co-funded basis from: (a) U.S. Department of Energy Grant No. DE-FG19-88BC14243 entitled "Proof of Feasibility of Thru Casing Resistivity Technology"; (b) U.S. Department of Energy (DOE) Grant No. DE-FG22-90BC14617 entitled "Proof of Concept of Moving Thru Casing Resistivity Apparatus"; (c) U.S. Department of Energy Grant No. DE-FG22-93BC14966 entitled "Fabrication and Downhole Testing of Moving Through Casing Resistivity Apparatus"; and (d) Gas Research Institute (GRI) Contract No. 5088-212-1664 entitled "Proof of Feasibility of the Through Casing Resistivity Technology". The government and the GRI have certain rights in this invention.