Mechanical Analysis and Safety Evaluation of Double-Packer String in a Horizontal Well

During the hydraulic compression packer setting process, axial stress of the string will be generated, which may affect the safety of the string. In this paper, the double-packer string in a horizontal well is taken as the object. Considering the two packers are seated separately, on the basis of Lame formula, generalized Hooke' s law and bar deformation theory, the equations of axial force and axial stress of the string from the packers, and the deformation of the string without constraint from packers are deduced under wellhead pressure. The results show that, when packer 1 is sealed with wellhead pressure as 10 MPa, the axial stress generated on the string between the bending section and packer 1 is 49.94 MPa. When packer 2 is sealed with wellhead pressure as 15 MPa, the axial stress generated on the string between the bending section and the packer 2 is 58.05 MPa. The axial stress of the string between packer 1 and packer 2 is reduced to 15.08 MPa and the total axial stress of the string between the bending section and packer 2 is 107.96 MPa. It can be seen that packer 2 increases the axial stress on the string between the packer and the bending section when it is seated and causes the axial stress of the string between packer 1 and packer 2 reduced. Thus, the dangerous point locates between packer 2 and the curved section of the string. The axial stress near the bottom of the string is reduced and the string tends to be safe. The results can be used to provide references for the selection of horizontal string to ensure its safety.