Thermoporoelastic model for fluid-driven debonding of cement during CO2 injection in a vertical well

Abstract

Well integrity is a critical challenge in carbon capture and storage (CCS) projects, where debonding of cement sheath can form preferential pathways for CO${}_2$ leakage. This study introduces a numerical framework for simulating fluid-driven debonding along the cement interfaces during CO${}_2$ injection. A pseudo-3D fracture propagation model, adapted to cylindrical well geometry, is coupled with a thermoporoelastic finite element mechanical model of the composite casing-cement-formation system. The framework accounts for poroelastic material behavior, thermal stresses, variations in fluid pressure and temperature, in-situ stress anisotropy, formation layering, and initial stress states induced by well construction and cement hydration. Fracture propagation is simulated in both vertical and circumferential directions, incorporating the effects of buoyancy, fluid viscosity, interfacial adhesion strength, and pressure-dependent leak-off. Numerical results reveal three distinct debonding regimes: crescent-shaped partial debonding, large incomplete debonding with non-monotonic aperture, and complete debonding that is characterized by a fully open channel around the circumference of the well. Sensitivity analysis reveals that debonding evolution is strongly influenced by cement shrinkage, injection conditions, cold fluid effects, and changes in reservoir stress over time. The model provides a predictive tool for assessing leakage risk and fracture evolution under varying cementing conditions, injection scenarios, and reservoir stress states.