Perpustakaan Digital ITB

This study evaluates the mechanical integrity of API Class G cement under injection-induced stress using Finite Element Modelling (FEM). A three-dimensional near-wellbore model was constructed to simulate the casing– cement–formation system, incorporating perforation densities of 2, 4, 6, and 12 shots per foot (SPF). Tensile and compressive failure were assessed based on stress thresholds (438 psi for tensile and 4380 psi for compressive strength) and a crack width criterion of 50 ?m. Simulation results show that tensile failure consistently occurs earlier than compressive failure, with cracks initiating and growing beyond the critical threshold after tensile stress is exceeded. Increasing perforation density improves stress distribution, resulting in higher critical bottom-hole pressure (BHP). However, it also leads to more severe crack propagation post-failure due to stress interaction between closely spaced tunnels. Two safety windows were defined: one based on stress response, and another on crack width evolution. Linear trendlines show strong correlation (R² > 0.83) between SPF and failure pressure, enabling predictive assessment. These findings highlight the dominant role of tensile stress in cement degradation and the trade-off between increased pressure tolerance and post-failure damage, providing useful insights for optimizing perforation strategies in well integrity design.