The theory of thermoporoelasticity has been widely discussed and presented invarious wellbore stability works. The breakdown gradient, defined as the pressurerequired to initiate fracture propagation, is strongly affected by temperature. In drillingscenarios, for example, cooling due to fluid circulation can induce losses to theformation. This work aims to investigate the influence of temperature variation on thebreakdown gradient in confined annular pressure build-up (APB) scenarios during wellproduction and containment. In well projects, to mitigate APB effects, the fracturegradient is used, corresponding to the minimum horizontal stress gradient or absorptiongradient. However, the initiation gradient is higher than these and can be furtherenhanced by temperature increase, which may lead to underdesigning of the well andeventual integrity failure. Additionally, the breakdown gradient is evaluated in ablowout situation and the rock s formation ability to withstand shut-in. To achieve theseobjectives, 1D geomechanical models were created and thermo-hydraulic simulationsof three wells were performed. A Mathcad® calculation spreadsheet was developed toincorporate the thermo-poroelastic effect in determining the breakdown gradient. As aresult, variations of up to 16 percent were found in the value of the breakdown gradient. Forthe analyzed wells, these variations imposed a significant redution in the well designsafety factors.