Try setting fire to it, that'll tell you whether it is methane. When I was in Azerbaijan a few years ago, they had a burning hillside that was quite impressive. Decided it was safer to do that than let it go, although why I don't know. Methane rises. They do have a mud field with bubbling escapes that looks spooky (named Clanger Land by the nearby BP people) but they don't set fire to that.

I also recall from the same visit a flame that had been from such natural sources had a shrine built around it in the middle ages and was an everlasting flame etc, (many shi'ite sects grew from fire worshippers) and this was OK till about fifty years ago, when the soviets started fracking, (or very similar) in nearby fields, causing the everlasting fire to extinguish.

When we visited it, they turn the gas on (via a metered pipe) for visitors. I took more photos of the pipe and meter than the medieval shrine if truth be known. Appealed to my sense of humour.