MELBOURNE, July 21 (Reuters) - Australia's Woodside Energy Group Ltd trimmed its production outlook for 2022 on Thursday and flagged a possible delay to a U.S. oil project inherited with BHP Group's petroleum assets, sending its shares down 4%. Woodside, now a top 10 global independent oil and gas producer following its merger with BHP's petroleum arm, said the Mad Dog Phase 2 oil project in the Gulf of Mexico, due to start operations in 2022, may face delays after problems were detected in some equipment. At the same time, it said it expects its full year output, excluding BHP assets, to be between 88 million and 94 million (mmboe), down 4 mmboe from its previous forecast, due to "new conversion factors", which analysts said was not well explained. "The market is confused and when these sort of complexities are poorly explained by the company, the market fears the worst. It's probably an overreaction today," said Dale Koenders, an analyst at Barrenjoey.