There are multiple factors that give rise to natural gas's much greater energy density:
- TNT carries its oxidizer internal to the molecule instead of getting it "free" from air
- TNT equivalent energy does not include full combustion of the oxygen-deficient detonation products, only instantaneous energy release during detonation
- TNT has a lower hydrogen:heavy atom ratio than natural gas
https://en.wikipedia.org/wiki/TNT_equivalent
1000 kg of natural gas has a lower heating value of 47.1 gigajoules, much greater than the 4.18 gigajoules per 1000 kg TNT equivalent.
The lower heating value of 67,000,000 kg of natural gas is 3.16 * 10^15 joules:
http://hydrogen.pnl.gov/tools/lower-and-higher-heating-value...
So more like 750 kilotons TNT equivalent.
There are multiple factors that give rise to natural gas's much greater energy density:
- TNT carries its oxidizer internal to the molecule instead of getting it "free" from air
- TNT equivalent energy does not include full combustion of the oxygen-deficient detonation products, only instantaneous energy release during detonation
- TNT has a lower hydrogen:heavy atom ratio than natural gas