I admit to being a "C" student in physics and I have a question that I suspect many people do.
What would happen if a nuclear weapon was detonated into the centuries of natural gas in Iran ?
Would we have the ultimate suicide bombing ?
As far as a potential big explosion? Probably nothing - the natural gas needs oxygen to burn.
If anything, it would probably loosen up the rock containing gas/oil deposits, making wells in that particular formation more productive.
If I'm not mistaken, we tried that ourselves about 40 or 50 years ago.