Patent ID: 7458421
Filing Date: 2008-12-02
Classification: E21B

Abstract:
1. A system for determining depth of a well-tool in a borehole penetrating an earth formation comprising: a wireline configured to couple with said well-tool and to suspend said well-tool in the borehole; a plurality of transponders disposed along the wireline at predetermined locations, wherein each of said predetermined locations define a measured length of the wireline; a reader for reading the plurality of transponders, wherein the reader is configured to receive a signal from each of the plurality of transponders when each of said plurality of transponders is located at a read position relative to the reader; a fiber optic cable coupled with the wireline, an optical signal generator coupled with the fiber optic cable and configured to generate an optical signal and transmit the optical signal through the fiber optic cable; an optical detector coupled with the fiber optic cable and configured to detect the optical signal, wherein the optical signal generator and the optical detector are positioned at a predetermined distance from each other on the wireline; and a processor capable of communicating with the reader and configured to receive an output from the reader and to process the depth of the well-tool in the borehole from the output and a time of flight of the optical signal between the optical signal generator and the optical detector.