CASING JOINT LOCATOR METHODS AND APPARATUS

摘要

A casing joint locator device (66) and methods are described. The locator device (66) includes a giant magnetoresistive (GMR) sensor (70) that is capable of detecting joints (24) between sections (20, 22) of casing in a wellbore. The methods and devices described detect perturbations in the earth's magnetic field caused by air gaps (34) and discontinuities associate d with a casing joint or with an external casing joint collar. As a result, th ey are capable of detecting flush and standard collared joints. The casing join t locator generates essentially no magnetic or electromagnetic field so that other downhole instrumentation is not affected by its presence.