An Investigation of the Effects of High Temperature and High Pressure (HTHP) On the Stability of Wellbore Casing Using Finite Element (FE) Method

Abstract

Abstract Casing is designed to provide well bore stability and withstand imposed loads such as external pressure, internal pressure and mechanical load due to compressive forces on casing. To ensure integrity and reliability of casings, a cost effective approach is hereby presented using finite element (FE) methods. At ordinary conditions of temperature and pressure, casing design can be achieved by the use of available grades of casing, but for HTHP wells it becomes critical to investigate the integrity and reliability of casing grades provided. Thus, numerical methods such as FE become invaluable as opposed to standard casing selection procedures. This work models stability of casing in the wellbore using a commercial industry accepted FE package – Abaqus 6.12. The model was developed using simple plane stress and plane strain elements with corresponding boundary conditions. Various mechanical properties of steel casing, concrete, surrounding rock and interfaces were modeled to mimic a full scale industry scenario. The model investigated casings under HTHP, mechanical failure criteria in terms of elasticity, plasticity of material, geometric non-linearity and compared with other existing analytical models in literature in other to validate the model. It was observed that the model becomes highly unstable under HTHP environment, hoop and radial strains in the wellbore casing increased as the temperature and pressure of the transported fluid in the wellbore increased. Areas of stress concentration in the casings can easily be observed in the model and it shows an efficient procedure for investigating the stability of casings in harsh conditions. Casings were subjected to HTHP to predict optimum configurations for different scenarios.