An Assessment of Slip Crushing in Drillstring Tension Design.

Among other forces considered during the design of drillstring, the effects of collapse pressure due to the presence of drilling fluids and tensile stress due to the length of the drillstring, both in a vertical wellbore, are the primary considerations in this work. Field data, drilling fluid specifications, wellbore geometry and American Petroleum Institute tubular specifications were applied. Recommended design procedures for bottom-top approach, with pressure-area force considerations were used to account for the effects of buoyancy. It was observed that all the initial designs were revised due to slip crushing safety element and margin-of-overpull. Nonetheless, the slip crushing problem was the most prevalent in the design conditions considered. The revised designs included replacement of some sections of the original 5-in. grade E drillpipes with similar E grade pipe, but with greater weight per foot types which had higher tensile strength. The maximum allowable load was used as an indicator of a properly designed drillstring, with tensile capacity of the pipes as basis for design. It is deduced that slip crushing might be expected in every first-pass assessment of drillstring design for tensile failure. [ABSTRACT FROM AUTHOR]