Abstract:

Well integrity depends on the mechanical stability of the casing-cement-formation system under thermo-mechanical loads induced by variations in temperature, pore pressure, and in-situ stresses. This study develops a numerical model for evaluating stress evolution in pre-stressed cased and cemented wells using a thermoporoelastic formulation. Two limiting loading conditions are examined: a newly created well, where the initial stress state is primarily governed by the cementing stage and volumetric shrinkage; and a late-life stage of the well's lifecycle, where both the cement sheath and the surrounding formation undergo dominant creep. The model accounts for poroelastic material behavior, thermal stresses, in-situ stress anisotropy, and casing eccentricity. To verify the implemented numerical algorithm, a closed-form analytical solution for the steady-state creep of an incompressible viscous medium around a circular cavity has been derived. Numerical simulations identify potential failure zones using the Drucker-Prager criterion. The results show that stresses established in the early stage are substantially reduced during creep-driven relaxation. In the case of long-term creep, the size of the potential failure zones decreases, reducing the risk of interfacial debonding or cracking. By explicitly incorporating the multi-stage construction history to define the initial stress state, the framework highlights the critical importance of a consistent initial-state formulation.