Numerical Investigation of the Impact of Geomechanical Parameters of Formations on Well Integrity of One of the Iranian Oil Fields

Well integrity is defined as the application of technical and operational solutions to reduce the uncontrollable risk of fluids leakage in the well lifetime. In any drilling and production operation, lack of knowledge about geomechanical behavior of the surrounding formations is considered as a major risk. Therefore, in-situ stress conditions and mechanical properties of formations are important factors in well integrity studies. In this paper, a 3D finite element model was built to simulate the integrity of wells. An FEM analysis was used to investigate the plastic deformation in cement and the Von Mises failure criterion inside the casings under different stress conditions, and to study the mechanical properties of the formation. A clear increase in plastic strain in the cement and Von Mises stress inside the casings was observed with increasing the ratio of horizontal to vertical stress in orthotropic and isotropic conditions as well as with increasing the difference between horizontal stresses in anisotropic conditions. When conducting the translation error sensitivity analysis, the impact of major mechanical parameters of the formation was evaluated as well. The results showed that by increasing Young's modulus, cement became hard and brittle. Meanwhile, an increase in the Poisson ratio led to plastic behavior. The maximum plastic strain was found at the cement-casing boundary due to the presence of a lower cement-formation friction value. The highest Von Mises stress value in the casings was also produced parallel toward the minimum horizontal stress. Additionally, with an increase in the cohesion and friction angle of formation, the cement became harder, and consequently, the safety factor for the casings increased.