Denver International Airport makes millions of dollars a year from more than 70 oil and gas wells on its expansive property, but a new city audit questions the operation with a key finding: nearly one-third of those wells are losing money. “The airport needs to take a closer look at whether it’s a good idea to continue operating wells that could be costing — instead of making — money on the airport’s land,” Denver City Auditor Tim O’Brien said in a news release Thursday.