The rig is operated by Petrobras, and was located in the Campos basin off the coast of Rio de Janeiro at the SS-53 Noble Paul Wolff platform when the incident occurred.
"The incident occurred due to flooding in one of the tanks of the vessel, caused by failure of the ballast system, which controls the stability of the valve unit," a Petrobras spokesman said in an emailed statement to Reuters.
Noble Corp. said that 77 non-essential personnel were evacuated from the rig with no reported injuries, and no pollution has been detected.
Noble Paul Wolff was built in 1980, and upgraded in 2006; the rig houses a maximum crew of 125.