BRASILIA, Dec 28 (Reuters) - Brazil's state-run oil company Petrobras is seeking 800 million reais ($152 million) in compensation from engineering group Odebrecht in arbitration proceedings over its alleged violation of the shareholders agreement in petrochemical company Braskem.

Petroleo Brasileiro SA, as the oil firm is known formally, said in a securities filing it had formalized the compensation request on Monday. Odebrecht is seeking to sell its 38.3% stake in Braskem SA, while Petrobras aims to offload its 36.1% stake.

($1 = 5.2461 reais) (Reporting by Jake Spring Editing by Chris Reese)