Peridynamics-Based Finite Element Analysis of Sealing Failure at Casing-Cement Sheath Interfaces in Ultra-Deep Wells

The number of ultradeep wells in China is increasing, and wellbore integrity concerns have become more urgent as the exploration and development of ultradeep oil and gas continue to progress. Long-term wellbore safety is at risk because engineering practice demonstrates that the casing-cement bonding interface, the weakest component of the wellbore structure, is prone to failure under coupled high temperature, high pressure, and complex in situ stresses. In this study, a thermo-mechanical coupling model of an ultradeep well composite system was developed using peridynamics. Quantitative simulations of the fracture of the casing-cement sheath interface under service circumstances were used to identify the main processes of interface failure under multifield coupling. The results demonstrate that damage primarily occurs along the path of minimum principal stress and that the progression of damage is significantly influenced by the nonuniform in situ stress coefficient, Poisson's ratio, and the elastic modulus of the cement sheath. The interface damage increases by around 40% as the elastic modulus of the cement sheath increases from 3 to 15 GPa and the Poisson's ratio climbs from 0.22 to 0.34. In contrast, casing pressure and formation temperature have less than 20% of an impact, but raising the nonuniform stress coefficient from 1.1 to 1.5 results in an 86.7% increase, with damage reaching 0.55 beyond 1.3 and causing sealing failure. The results of this work promote the optimization of material parameter selection, increase wellbore integrity and sealing dependability, and enhance the safety and long-term stability of essential structures. These findings offer engineering direction for the design of ultradeep wellbores.