This paper studies the frictional drag of helically buckled pipes (drillstring and tubing) in extended reach and horizontal wells to correctly predict the actual bit weight or packer load, in cases where helical buckling of pipes may have occurred. Helical buckling of pipes in such wells may occur, since large axial loads are often required. The differential equation of axial force balance with consideration of the axial friction for helically buckled pipes is resolved, and the solution shows that when the pipes are helically buckled, the frictional drag will become very large. The actual bit weight for drilling or packer load for well completion may therefore become much smaller than estimated under the unbuckled pipe conditions. The analytical solution is also shown to agree with the results from laboratory experiments, which simulate the real wellbore-pipe conditions. An example is provided to show the calculation procedure and the importance of the results.

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