A cased well in the earth is electrically energized with A.C. current. Voltages are measured from three voltage measurement electrodes in electrical contact with the interior of the casing while the casing is electrically energized. In a measurement mode, A.C. current is conducted from a first current carrying electrode within the cased well to a remote second current carrying electrode located on the surface of the earth. In a calibration mode, current is passed from the first current carrying electrode to a third current carrying electrode located vertically at a different position within the cased well, where the three voltage measurement electrodes are located vertically in between the first and third current carrying electrodes. Voltages along the casing and resistances along the casing are measured to determine wall thickness and the location of any casing collars present so as to electrically inspect the casing. Similar methods are employed to energize a pipeline to measure the wall thickness of the pipeline and the location of pipe joints to electrically inspect the pipeline.
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 (DOE) 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. The application herein was filed during periods of time funded by (c) and (d) above.