Mechanical Deformation Regular Pattern Of Cement Ring And Its Influence On Structural Integrity

During the production process of oil wells and gas storage wells,the integrity of shafts,especially the structural integrity of cement rings,plays an important role in ensuring the safety of production.This paper is on the basis of studying the deformation regular pattern of cement ring,established three mechanical constitutive equations under triaxial stress,ideal elastoplastic model,linear-hardening model and nonlinearity elastoplastic model;according to the creep heterogenetic crustal stress condition,based on mechanical model of casing-cement-sheath assembly,analyzed the influence of the cement ring with different regular patterns to mechanical integrity of the assembly during loading and unloading.The study provides a basis for reasonably selecting the mechanical parameters of cement ring and guiding the design of cement slurry system.The results show that three constitutive relations of idea elastoplastic,linear-hardening and nonlinearity elastoplastic of the cement ring have different effects on the its interfacial stresses.In the same conditions,when the cement rings are not yielding,the interfacial stresses of cement rings with different three constitutive relations are basically the same;and when the cement rings are yielding,the cement ring with nonlinearity elastoplastic constitutive relation has the maximum interfacial stresses during loading,and is prone to compression,tension and shear failure;the cement ring with idea elastoplastic constitutive relation has minimum interfacial stresses during unloading,and is prone to interfacial fracture.Therefore under the deep well,ideal elastoplastic and inear-hardening constitutive equations should not be used to simplify calculate the interfacial stresses of cement ring,but in the location of low crustal stress,ideal elastoplastic and inear-hardening constitutive equations can be used to simplify calculate the interfacial stresses of cement ring.