Exxon Mobil Corp roared into Brazil’s prolific offshore oil fields again on Thursday, clinching eight blocks in partnership with other oil firms eager to lap up the country’s choice reserves ahead of presidential elections later this year.  Exxon along with Petrobras and Qatar Petroleum Intl shelled out 2.8 billion reais ($844 million) for a block in Brazil’s offshore Campos basin as the American oil major seeks to replace dwindling reserves. Chevron Corp, Repsol SA, Royal Dutch Shell Plc, BP Plc and Statoil ASA also spent top dollar to lock down stakes in Brazilian offshore blocks, some of which may be part of the coveted pre-salt play, where oil is trapped under layers of salt beneath the ocean floor. […]