Casing Inspection Logging Tool

Abstract

An instrument assembly for a well casing inspection tool, comprising a main shaft having an extension shaft extending therefrom. An instrument head is supported on bearings proximate one end of the main shaft. The rotating instrument head, which includes sensors for measuring wall thickness and caliper of the well casing, provides continuous 360 degree scanning of the interior of the well casing to obtain detailed measurements of the well casing. A motor drives the rotating instrument head through a gear train. A mandrel supported by the main shaft includes exciter coils for wall thickness, caliper, and permeability measurements. A capacitive slip ring couples signals between the rotating instrument head and stationary circuits in the instrument assembly.

1 . An instrument assembly for a well casing inspection tool, comprising:
 a main shaft having a hollow portion and an extension shaft extending axially from a first end of said main shaft; and   an instrument head concentric with and configured for free rotation about said extension shaft and proximate said first end of said main shaft; wherein   said rotating instrument head provides continuous 360 degree scanning of the interior of said well casing to obtain detailed measurements of said pipe casing.   
     
     
         2 . The instrument assembly of  claim 1 , wherein
 said instrument head includes sensors for measuring wall thickness of said casing.   
     
     
         3 . The instrument assembly of  claim 1 , wherein
 said instrument head includes sensors for measuring caliper of said casing.   
     
     
         4 . The instrument assembly of  claim 1 , further comprising:
 an electric motor disposed within said hollow portion of said main shaft, said motor having an axial output shaft.   
     
     
         5 . The instrument assembly of  claim 4 , further comprising:
 a gear train including a counter-shaft for mechanically coupling said instrument head to said electric motor axial output shaft for causing said rotation of said instrument head.   
     
     
         6 . The assembly of  claim 1 , further comprising:
 a mandrel supported on said main shaft and having at least one exciter coil disposed thereon.   
     
     
         7 . The assembly of  claim 1 , further comprising:
 at least one bearing for supporting said instrument head upon said extension shaft and enabling said rotation of said instrument head.   
     
     
         8 . The assembly of  claim 1 , wherein said instrument head comprises:
 first and second sensor assemblies for measuring respectively at least caliper and wall thickness of said well casing; and   first and second electronic circuits respectively coupled to said respective said wall thickness and said caliper sensor assemblies.   
     
     
         9 . The assembly of  claim 1 , further comprising:
 a capacitive slip ring assembly for coupling electrical signals between circuits of said rotating instrument head and circuits disposed in said main shaft.   
     
     
         10 . The assembly of  claim 1 , wherein:
 said main shaft, said mandrel, and said rotating instrument head combination are enclosed within a housing assembly comprising:   a stainless steel sleeve having a thin walled construction; and   a ceramic sleeve for enclosing said rotating instrument head.   
     
     
         11 . A well casing inspection instrument, comprising:
 an elongated instrument body having a longitudinal axis;   a main shaft supported in said elongated body along said axis;   a motor mounted in said main shaft and aligned along said axis; and   a rotating sensor assembly supported by a bearing assembly on an extension of said main shaft and driven by said motor;   wherein said rotating sensor assembly provides continuous 360 degree scanning of the interior of said pipe casing to obtain detailed measurements of said pipe casing.   
     
     
         12 . The instrument of  claim 11 , wherein said rotating sensor assembly is configured for measuring the wall thickness of said well casing. 
     
     
         13 . The instrument of  claim 11 , wherein said rotating sensor assembly is configured for measuring the caliper of said well casing. 
     
     
         14 . The instrument of  claim 11 , wherein said rotating sensor assembly is configured for measuring the permeability of said well casing. 
     
     
         15 . The instrument of  claim 11 , wherein said rotating sensor assembly is configured for measuring at least one of the well casing parameters selected form the group consisting of wall thickness, caliper, and permeability. 
     
     
         16 . The instrument of  claim 11 , further comprising:
 a gear train coupling a drive gear on an output shaft of said motor with a driven gear on said rotating sensor assembly.   
     
     
         17 . The instrument of  claim 12 , further comprising:
 a first exciter coil installed on a mandrel for activating a wall thickness sensor in said rotating sensor assembly.   
     
     
         18 . The instrument of  claim 13 , further comprising:
 a second exciter coil installed on a mandrel for activating at least one caliper sensor in said rotating sensor assembly.   
     
     
         19 . The instrument of  claim 11 , further comprising:
 a permeability exciter coil installed on a mandrel for activating a permeability sensor in said rotating sensor assembly.   
     
     
         20 . The instrument of  claim 11 , further comprising:
 a capacitive slip ring assembly for coupling output signals from circuit terminals on said rotating sensor assembly to circuit terminals of a non-rotating processing circuit disposed in said instrument body.   
     
     
         21 . The instrument of  claim 11 , further comprising:
 at least first and second ball bearings interposed between said rotating sensor assembly and said main shaft.   
     
     
         22 . The instrument of  claim 11 , wherein said elongated instrument body further comprises:
 a centralizing mechanism for axially centering said instrument body.   
     
     
         23 . A casing inspection tool, comprising:
 a tool body;   a main shaft having a first diameter and a first end and disposed in said tool body, said main shaft having a hollow first portion proximate said first end;   an extension shaft of smaller diameter extending longitudinally from said first end of said main shaft; and   a rotating sensor assembly supported on said extension shaft by a bearing assembly and driven by a DC brushless motor supported within said hollow portion, said sensor assembly including:   a high resolution wall thickness sensor for scanning the entire wall of said casing to obtain continuous detailed wall thickness data; and   a high resolution caliper sensor for scanning the entire wall of said casing to obtain continuous detailed caliper data.   
     
     
         24 . The apparatus of  claim 23 , further comprising:
 a gear train coupled between a drive gear on an output shaft of said DC brushless motor and a driven gear on said rotating sensor assembly.   
     
     
         25 . The apparatus of  claim 24 , wherein said gear train comprises:
 a first gear set providing a first reduction in output shaft RPM;   a second gear set providing a second reduction in output shaft RPM; and   a countershaft coupling said second gear set to said first gear set.   
     
     
         26 . The apparatus of  claim 23 , further comprising:
 an exciter coil mandrel;   a low frequency exciter coil for said wall thickness sensor; and   a high frequency exciter coil for said caliper sensor.   
     
     
         27 . The apparatus of  claim 26 , further comprising:
 a permeability coil supported on said mandrel for correcting said wall thickness data.   
     
     
         28 . The apparatus of  claim 23 , further comprising:
 a capacitive slip ring connector, comprising:   rotating concentric conductive rings supported on said rotating sensor assembly and coupled to outputs of said sensors; and   stationary concentric conductive rings supported on said mandrel and coupled to inputs to a processor.