Methane is the largest component of natural gas, a large percent of our energy resources. As CH4, it doesn't really decompose into anything.
(You do need large quantities of concentrated gas to make use of it though: Diffuse little bits mixed in amidst tons of muck isn't practical to even gather, much less transport and try to use.)
See post 93. CH4 does convert to CO2 over time (decades) in the atmosphere. Summarized grabbed from Wikipedia:
"This is the case for methane. It is oxidized by reaction with naturally occurring hydroxyl radical, OH· and degraded to CO2 and water vapor at the end of a chain of reactions (the contribution of the CO2 from the oxidation of methane is not included in the methane GWP)." GWP = global warming potential