A method for simulating the effects of rupture disk failure on annular fluid expansion in sealed and open annuli to mitigate annular pressure buildup in a wellbore comprises the steps of: determining whether an internal region or an external region for a pair of casing string annuli is open; and calculating at least one of an adjusted internal annular pressure buildup and an adjusted external annular pressure buildup for at least one of the internal annular region and the external annular region of the casing string annuli.