Buckling Analysis Of Unsealed Casing Column In Well

This article is from the cooperation projects of Tarim Oilfield——the sidetracking feasibility analysis of lateral drilling. It analyzed the buckling behavior of not solid cement and free period of casing string in the eyes of the well by means of theoretical analysis and modeling analysis. When free period of casing string occurs buckling, casing string bends along the sidewall, leads to additional force, additional bending moment, reduces the ability to resist broken of casing string, weaken the strength of casing string thread connection and causes the eccentric wear of the drill string when lateral drills. If casing string’s deformation is too large, it will cause casing string damage, packer invalidation and so on. The study of not cementing of casing string buckling is important to the feasibility of lateral drilling.The free period of casing string is the research object of this paper. Considering the self-weight of casing string, fluid pressure inside and outside of casing string, temperature of the hole, contact for caned frictional between the casing string and hole, which could describe buckling behavior’s differential equation derived by the traditional constitutional method and energy method.(l)Solve the differential equation of casing buckling by perturbation method and energy method. Study two buckling deformation pattern, include of sinusoidal buckling and spiral buckling of the casing string. Get the analytical solution of sinusoidal buckling and spiral buckling of the casing string’s buckling configurations, which changes along the string. In cooperation to numerical calculation, the results show that the analytical solution and numerical solution of the differential equation for buckling are unanimous.(2) The buckling differential equation is dimensionless. Determine the critical load of sinusoidal buckling and spiral buckling. And systematically analyze the load, stress and deformation of the casing string, including the contact force of casing string and borehole wall, the axial load of casing string and bending moment of casing string and so on.On the basis of theoretical analysis, by the parameterization and command flow, directly established the casing string’s finite element simulation model in the well which is using the finite element analysis software ANSYS.(1)Analyze the free period of casing string’s buckling with the finite element simulation model and the contact force and friction force of casing string and borehole wall. (2)Combining with solution of buckling differential equation, confirm the rationality of the model and analysis method in this paper.(3)Analyze the thread model setting up. The appropriate contact force is advantageous to the thread sealing, but too large contact force can make the thread tripping mesh from beginning, lower sealing ability.