Woodside Petroleum has been forced to shut down its $15 billion Pluto liquefied natural gas plant in Western Australia after a drilling rig was torn from its moorings in a cyclone and drifted dangerously close to flowlines at the offshore field. Pluto is Woodside's biggest single production asset and was the largest contributor to earnings last year, and the shutdown could impact production, profits and dividends, depending on how long it lasts, said UBS analyst Nik Burns.