Natural gas: How energy resides
Lots of energy per kilo, almost none per litre
What this tab covers The physical form in which the energy is held or carried, where it comes from, the chain of transformations that put it there, and how concentrated it is.Natural gas, mostly methane, stores ancient solar energy in the bonds of the smallest hydrocarbon molecule. It has high energy per kilogram but very little per litre unless compressed or liquefied.
Form Chemical energy in methane (CH4) and light hydrocarbon gases Origin Fossil solar (ancient photosynthesis), via deep heating or microbial actionHow it got there
Fusion in the Sun Sunlight Photosynthesis by plankton, algae and land plants Burial of organic matter Deep heating cracks kerogen and oil into gas (or microbes generate methane in shallow sediments and coal) Gas migrates into reservoirs or stays in shale and coal seamsHow concentrated it is
| Measure | Value | Note |
|---|---|---|
| Natural gas, net calorific value by mass | 48.0 (range 46.5 to 50.4) MJ/kg1 | Highest of the fossil fuels per kilogram. |
| Natural gas by volume (US average) | 1,036 Btu per cubic foot, about 38.6 MJ per cubic metre (converted) MJ/m3 at standard conditions2 | Gross heat content. One cubic metre of gas holds about a thousandth of the energy of a cubic metre of oil. |
| Liquefied natural gas (LNG) | about 600 times smaller volume than gas, cooled to about minus 260 F (minus 162 C) volume ratio3 | About 23 GJ per cubic metre of liquid (calculated), enough for ocean shipping. |
| Gas formation temperature | above about 150 to 160 degrees C4 | Above the oil window, kerogen and oil crack mainly to gas. |
Most natural gas is thermogenic. It forms when buried organic matter, or oil already formed from it, is heated beyond about 150 to 160 degrees C and cracks into small molecules. Some is biogenic, made by microbes at shallow depth, as in much coalbed methane. Conventional gas has migrated into porous reservoir rock under a seal. Shale gas never left its fine-grained source rock. Tight gas sits in low-permeability sandstone, and coalbed methane is adsorbed on the internal surfaces of coal.
Per kilogram, methane carries more energy than oil or coal, and it burns cleanly. Its handicap is volume: at room pressure a cubic metre holds only about 39 MJ. Moving gas therefore needs pipelines at high pressure, or liquefaction to LNG, which shrinks it about 600 times but costs energy and capital. This is why gas markets were long regional and why gas produced far from pipelines is often flared.
Sources
- 2006 IPCC Guidelines for National Greenhouse Gas Inventories, Vol. 2 Energy, Ch. 1 Introduction (Tables 1.2 and 1.4) IPCC, 2006
- Units and calculators explained: British thermal units (Btu) US EIA, 2024
- Natural gas explained: liquefied natural gas US EIA, 2024
- How are oil and gas formed? Wyoming State Geological Survey, 2024