Analysis of Limit Setting Force of Casing Inside Slips Based on Cylindrical Shell Theory

摘要

Casing will be damaged in a well because of the setting force, and may even be broken when the force is toolarge. To clearly demonstrate the interaction of the mechanism of packer and casing, a mechanical model of casing asthin-wall cylinder was established with the consideration of the axial force and additional bending moment induced by thebending of casing near the slips of packer. And, the equation of limited setting force on the Casing exerted by slips wasdeduced by bending moment theory of cylindrical shell. The relationships of the limited setting force of N80, P110,TP140 casing and thickness were analyzed. It was found that the bending stress and the hoop stress were biggest near thebottom of the slips, and that position was the dangerous section. The limited setting force of Casing exerted by slipsincreased with the thickness of casing, when the packer and the outer diameter of casing remained the same. And thelimited setting force was higher in high grade casing. The limited setting force calculated in this paper was decreased 5 %to 14 % than by thick-wall theory, and it is deduced to be safer. The method proposed in the paper can be used to evaluatethe limited setting force and provide the basis for the choice of hanging load.