Novel Method for Optimization Cement Slurry Based on the Wellbore Integrity Model in High-Temperature and...

The integrity of the cement sheath is crucial for ensuring the long-term safe and efficient production of oil and gas wells. The mechanical properties of the cement sheath are improved by optimizing the cement slurry to match the actual operating conditions, further enhancing the wellbore integrity. In high-temperature and high-pressure (HTHP) conditions, a mechanics model of casing-cement sheath-formation was developed based on the thick-walled cylinder theory, considering the coupling effect of temperature and pressure as well as elastic and plastic deformation of the cement sheath. The relationship between the mechanical parameters of the cement sheath, such as elastic modulus, Poisson's ratio, and yield strength, and casing pressure under different temperatures was analyzed based on the simulation results. A control chart of the mechanical properties of the cement sheath under high-temperature and high-pressure environments was subsequently developed. It was concluded that the elastic deformation of the cement sheath occurs first followed by plastic deformation as the casing pressure increases, corresponding to the yielding point of tangential stress on the cement sheath. The cement sheath is more prone to failure in high-temperature conditions due to thermal stress. Sensitivity analysis revealed that a cement sheath with a low elastic modulus and high yield strength contributes to enhancing its integrity. The developed control chart enables a quick and quantitative estimation of whether the cement sheath meets the requirements of downhole conditions. Most importantly, the cement slurry is optimized, based on the theoretical method, to improve the seal integrity of the cement sheath. This study provides a quantitative evaluation of cement slurry optimization and offers practical guidance for managing the wellbore integrity by identifying the mechanical parameters of cement sheaths under operating conditions.