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US 4,808,925 AGranted
Three magnet casing collar locator
AssigneeHalliburton Company
InventorGary K. Baird
Life of this patent
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Abstract
For use with casing having flush joint collars, a detection system is set forth which comprises a tool body made of nonmagnetic material and enclosing abutted first, second and third permanent magnets. The magnets are axially aligned, abutted so that opposing poles are in contact with one another, thereby forming a magnetic field from the center magnet which is focused out into the metal of the casing. Separate detection coils spaced along the tool body detect signals induced by variations in magnetic reluctance as the tool traverses the cased well.
Claims6
A casing collar locator, comprising:
- (a) a non magnetic downhole tool body sized and adapted to be lowered axially in a well borehole;
- (b) three serially positioned permanent bar magnets carried interiorly of said body and abutting at opposing poles wherein the center magnet forms a magnetic field directed outwardly therefrom and the magnetic field is focused radially outwardly by the remaining two magnets to magnetically interact with tubular member threaded joints in the well borehole;
- and
- (c) detection coil means wound over said magnets and located at the juncture of said opposing poles of said magnets to detect changing magnetic field signals from the threaded joints coupled thereto by the focused magnetic field.
1 more element
Dependencies are inferred from the claim text.