Method and apparatus for measuring internal casing wear

Abstract

A method of identifying the presence, type and extent of internal casing wear and distinguish worn casing from various types of unworn casing. Two inspection instruments are tied together in the combination traverses a section of casing where information on internal wear is desired. The first inspection instrument generates two signals related to the minimum and maximum wall thickness present at each location within the casing section. The second inspection instrument generates a signal related to the degree of phase shift at each location of the casing section. The present invention analyzes these three signals and generates a differential crossplot whereby for each location of the casing section, a point-pair is plotted, both points of the point-pair having the same phase shift curve differential (calculated from the degree of the phase shift data series) as the X-coordinate and a maximum and minimum radius curve differential (calculated from the minimum and maximum wall thickness data series respectively) as respective Y-coordinates. Analysis of the differential crossplot may then be made, either along or in conjunction with the calculated round casing line to identify the presence, type and extent of internal casing wear and distinguish worn casing from various types of unworn casing.