Design, realization and field results of an inductive casing collar locator

During well logging operations, the depth of a logging tool is usually obtained from measuring the length of the wireline cable that suspends the tool in the well. In some cases, a secondary depth reference is obtained by detecting the collars along the casing pipe which lines the well. For small, untethered sensor platforms neither method is practical. This paper describes an inductive sensor which detects the fine gap on the inside of the casing where two pipe joints come together within a collar. The detector consists of two identical short solenoid coils with a common axis. A wired prototype tool was designed, built and tested in the field. Results from the field trial show clear a signal for the casing collars and are agreement with the results from simulations. The signal trend is in agreement with pipe inspection trends published in the literature.