Patent ID: 8121788

Claim:
A method for correcting errors in logging-while-drilling (LWD) depths, comprising: executing, via a processor, program instructions capable of: performing torque and drag model analysis using drillstring weight, downhole friction, weight on bit, thermal expansion, rig heave and tide to produce a corrected time-depth file, wherein the torque and drag model is automatically calibrated using effective block weight, drillpipe wear, and sliding friction; and correcting time-based LWD data using the corrected time-depth file to produce depth-corrected LWD data, wherein the torque and drag model is calibrated by performing: calibrating the effective block weight to match in-slip actual hookload (ISAH); calibrating the mud weight to match rotating actual hookload (RAH) and rotating model hookload (RAM); and calibrating the effective sliding friction to match TIAH/TIMH and TOAH/TOMH, wherein TIAH is trip-in actual hookload, TIMH is trip-in model hookload, TOAH is trip-out actual hookload, and TOMH is trip-out model hookload; and estimating an uncertainty of a mechanical stretch due to at least one of drillpipe wear and sliding friction by steps comprising determining a scattering of the TIAH and TOAH: and introducing scattering into at least one of the drillpipe wear and the sliding friction to match the scattering of the TIAH and TOAH.