<p>Packers are critical components in oil and gas well production and completion processes. Their rubber elements ensure effective annular isolation under diverse operating conditions. However, casing deformation can severely degrade the sealing performance of packer rubber elements, potentially leading to seal failure. This study investigates the failure mechanisms of packer rubber elements under casing deformation, focusing on structural simplification of compression packers, numerical modeling, deformation classification, and the establishment of a hyperelastic constitutive model for rubber materials. Tensile and compressive stress–strain experimental data were used to calibrate the Yeoh model, which was applied to evaluate the sealing performance of rubber elements under different casing deformation modes. Casing deformations were classified into four primary modes: eccentricity, ovality, inner diameter variation, and inclination. Finite element simulations were conducted using simplified pipe geometries to analyze the impact of each deformation mode on sealing performance. Simulation results show that casing deformations significantly affect contact pressure distribution and sealing length. Higher contact pressure and longer sealing lengths on the inner sealing surface enhance sealing performance. However, all deformation modes cause localized pressure reductions in low-contact-pressure regions and reduced sealing lengths, thereby increasing the risk of seal failure. Among these factors, eccentricity most significantly affects contact pressure distribution, whereas inner diameter variation has a relatively minor impact. Moreover, eccentricity and inclination show nonlinear effects on sealing performance, while ovality and inner diameter variation exhibit relatively stable impacts. This study highlights the critical role of casing deformation in packer rubber element failure, addressing a previously overlooked factor in sealing performance evaluation. The findings offer valuable theoretical insights for optimizing packer design and material selection, while proposing a systematic methodology to evaluate sealing performance under deformed casing conditions. These results contribute significantly to improving the reliability and safety of oil and gas well operations.</p>