Analysis Of The Influence Of Cement Ring Defects On The Bearing Capacity Of Threaded Joints Of Casing Joints

The cement sheath defect nearby casing joint will directly affect the forces condition of its threads.And always result in stress concentration phenomenon,even lead to casing damage.However,there is a bit of research at home and abroad about influence of the cement sheath defect nearby casing joint on casing threads strength.Besides,the considered factors of established strata-cement sheath-casing joint system model are not comprehensive.Based on the elasticity,this paper,firstly,simplify the problem for the case of plane strain,establish an equivalent stress computation model,when the cement sheath is intact and casing joint is under the uniform earth stress.Next,considering the deformation coordination of casing joint's internal and external threads,deduce the stress distribution calculation model of casing joint's threads,when the cement sheath is intact and casing joint is under the uniform earth stress.Promoting the calculation method of casing threads,three-dimensional,stress distribution with cement defects on this basic.Then established many cement sheath defect model with different parameters,according to the profile data of site.In the case of neglecting the axial load,models with various cement sheath defects were simulated by finite element software to obtain the corresponding threads stress distribution.Then,discuss the impact of bearing capacity when different types of loads and different cement sheath defect interact.Finally take the axial load into account,give the maximum equivalent stress calculation method of casing threads with cement ring defects under complex working conditions and the influence degree factor of different axial loads.And get the following conclusions:(1)The theoretical method proposed in this paper at Chapter two is applicable to calculate the stress of the casing in the shallow well with the low axial tension or the casing in horizontal well without the axial tension.With the high axial tension,calculation should apply the modified formula.(2)The deformation coordination factor of the threads does not change with the size of the load,but only changes with the geometric parameters of the model and the type of load.(3)Axial tension will not change the influence of defects on the bearing capacity of the casing thread,only enhance the impact of defects with a certain percentage of m.(4)The casing threads maximum equivalent stress with the first interface defects is always more different from than the second interface.Casing eccentricity can exacerbate the effect of defects.