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Abstract This study focuses on understanding the physics of circulating a CO2 kick out of a subsea well and determining the impact at the surface choke and the mud-gas separator when the kick passes through. A computational fluid dynamics (CFD) model that replicates the thermophysical properties of CO2 is used. Analogous CH4 scenarios are also analyzed, juxtaposing the impacts of both fluids. Eight scenarios are evaluated, covering variations in kick type (CO2 or CH4), kick volume (10 or 20 bbls), kick intensity (0 or 0.6 ppg), circulation rate (3 or 1.5 bpm) and drilling fluid type (oil-based or water-based). This defines a sufficiently broad simulation space to gain insight into this previously undefined aspect of well control when drilling through CO2-charged zones. We find that circulating out CO2 kicks using an oil-based drilling fluid can result in choke line temperatures that easily plunge below −50° F for a 10-bbl kick, and down to −150° F for a 20-bbl kick. This radical drop in temperature does not, however, occur when the CO2 kick is circulated out in a water-based drilling fluid. Additionally, if wellbore pressures are sufficiently low while circulating out a CO2 kick using oil-based drilling fluid (like during a low kick-intensity scenario), CO2 can break out of solution and create hydrate/ice-forming conditions in the choke line between the rig floor and the subsea BOP. In such conditions, holding additional backpressure in the choke line and wellbore can assist in forestalling CO2 breakout until the kick/drilling-fluid mixture reaches the surface choke.