A pair of ongoing studies show unexpectedly high methane leakage from some oil and gas fields in the U.S., findings that underscore concerns that the climate benefits of the natural gas boom may be overstated. Researchers from the University of Colorado at Boulder say new data indicates that as much as 4 percent of methane from a production area in Denver is leaking into the atmosphere, echoing findings first reported in a much-disputed study published last year in the Journal of Geophysical Research. A separate field study in Utah suggested even higher methane leakage rates of 9 percent. The calculations were made based on aerial and ground-based measurements and atmospheric models that estimated the level of emissions required to produce the recorded concentrations. “We were expecting to see high methane levels, but I don’t think anybody really comprehended the true magnitude of what we would see,” said Colm Sweeney, of the federal Earth System Research Lab Aircraft Program.