Drill string whirl and buckling cause impact-rub contact against the casing inner wall, which induces casing wear and threatens wellbore integrity. This study incorporates both whirl and buckling to analyze the wear mechanism. Finite-element dynamic models are established for three drill string states: stable unbuckled, sinusoidally buckled, and helically buckled. Transient dynamic simulations are performed in the ANSYS Workbench Transient Structural module to obtain whirl trajectories, contact pressures, and contact characteristics at multiple sections along the string. A casing-wear volume calculation based on the Kumar–Samuel formulation with time-varying contact pressure is then used to quantify wear at the lower drill collar, the upper stabilizer, the upper drill collar, the heavyweight drill string, and the buckled segment. Results show that once buckling occurs, whirl concentrates in the bottom-hole assembly and decays progressively from the bottom of the well toward the wellhead. Casing wear increases across all locations, with the largest increments at the lower drill-collar interval and within the buckled segment. Helical buckling produces greater casing wear than sinusoidal buckling. Neglecting drill string buckling, especially helical buckling, leads to underestimation of casing wear and thus underestimation of wellbore-integrity risk.