Analytical methodology for wellbore integrity assessment considering casing-cement-formation interaction

A wellbore analysis presents several challenges regarding the drilling, construction and production phases. Owing to that, the cement and casing stress states during the wellbore lifespan are also difficult to predict. Nevertheless, analytical solutions can reach good results. Additionally, once analytical approaches are exhibited as mathematical expressions, they facilitate the assessment of the interaction between variables and the impact on results. On the other hand, wellbore analytical solutions do not usually consider all the phases involved. In this work, an analytical solution is developed to assess the stresses during the drilling, construction and production phases. Three models are adopted to be compared with a numerical approach. Thus, single and double casing configurations are analyzed. In both approaches, the initial stress states in the formation and in the cement, as well as the drilling operation, the casing run, the pressure changes, and the pore pressure variations are considered. The solutions consider plane strain conditions, continuous homogeneous isotropic media and linear elastic materials. In addition to the casing integrity, radial and tangential stresses for casing, cement and formation are presented. In conclusion, this analytical solution reaches excellent results when compared to the numerical model, therefore, becoming an alternative for the stress evaluation for everyday scenarios. Capable of simulating different scenarios regarding the wellbore stresses and integrity, this analytical solution is a good tool for a preliminary design.