Methods and systems for robust and accurate determination of wireline depth in a borehole

A method for determining depth of a well-tool in a borehole penetrating an earth formation where the well-tool is suspended in the borehole from a wireline, comprising the steps of;

• moving the wireline into the borehole to position the well-tool;
• using a set of odometer wheels to measure length of the wireline moved into the borehole;
• transmitting the length measured by the odometer wheels to a processor;
• receiving at a receiving location data from at least one of a plurality of transponders passing the receiving location as the wireline is moved into the borehole, wherein the plurality of transponders are disposed at predetermined locations along the wireline;
• transmitting the received data to the processor;
• measuring a time of flight of an optical signal passing through a fiber optic cable coupled with the wireline;
• wherein;
• the time of flight is measured between a first optical grating and a second optical grating, and wherein the first and second optical gratings are disposed along the fiber optic cable;
• the first and the second optical gratings are disposed at predetermined distances along the wireline, and
• a first and a second transponder from the plurality of transponders are positioned at a same location as the first and the second optical gratings, respectively
• transmitting the time of flight to the processor;
• and
• processing the depth of the well-tool in the borehole penetrating an earth formation from the length measured by the odometer wheels, the data received from at least one of the plurality of transponders and the time of flight.