Casing strength degradation due to torsion residual stress in casing drilling

Casing string is rotated by torque from wellhead during casing drilling. The method to determine casing torsion status under various torques in casing drilling was discussed. There are three different torsion statuses under different torques, including elastic torsion, elastoplastic torsion and plastic torsion. The residual stress distribution was also discussed under different torques. The average residual stress under elastoplastic and plastic torsion status was calculated respectively; The modified casing collapse strength formula was derived considering the effect of residual stress. The analysis of calculation results indicates that the residual stress caused the collapse strength to decrease 0.033% under elastoplastic torsion, and effects of residual stress on casing strength can be neglected when there is no geometry shape changes in the casing.