Cement Integrity Evaluation Under Internal Casing Pressure Change And High Temperature

Failure of cement sheath is an important factor affecting the integrity of oil and gas wells.In the process of drilling completion and production,if the cement sheath seal fails,it will affect to the wellbore safety,environmental pollution and well productivity.Variation of casing pressure and high temperature are two important factors affecting the integrity of cement sheath.In this study,finite element method and theoretical analysis method were used to study the failure mechanism of casing and the failure mechanism of cement sheath under high temperature and pressure conditions.The influence of casing performance parameters,cement ring parameters and formation parameters on cement ring failure was discussed.Through the stress distribution law and radial displacement of the wellbore system,a method is established to determine the failure of cement sheath.The effects of parameters such as Young's modulus,Poisson's ratio and cohesion on cement stress were analyzed in finite element model analysis in ABAQUS.The influence of parameters such as Young's modulus,Poisson's ratio and cohesion on cement stress was analyzed.It was found that the deformation of cement in the perforation area decreased with the increase of Young's modulus,Poisson's ratio and cohesion.Based on the principle of elastic mechanics,the calculation model for "casing-cement-formation" stress displacement under high temperature conditions were established.The influence of casing parameters,cement sheath parameters and formation parameters on the thermal stress of cement were discussed.It was found that the largest Von Misses thermal stress and circumferential stress were located in the outer wall of the cement,and the maximum radial thermal displacement and maximum radial compressive stress appeared in the inner wall of the cement ring.The thermal stress of the cement sheath increases with the increase of the expansion coefficient and Young's modulus.Finally,cement ring failure criterion is established by tensile failure,shear failure and equal stress damage coefficients.Through these criteria,the failure condition of cement ring under different working conditions can be judged.The research results can provide the basis for the evaluation of the integrity of cement sheath seal.