How does heating kerogen release liquid and gaseous hydrocarbons?

The release of liquid and gaseous hydrocarbons from kerogen is achieved through a process called pyrolysis. Because kerogen is a complex, solid macromolecular mixture, it must be heated to break its chemical bonds.12

When heat is applied—either aboveground in retorts or underground in situ—it triggers the thermal degradation and cracking of these large molecules. This process effectively breaks the heavy hydrocarbon chains into smaller, more mobile molecules that manifest as liquid and gaseous hydrocarbons.231

The specific conditions of this transformation depend on the method used:
* Aboveground (Ex Situ): Rapid heating in oxygen-free vessels at temperatures typically ranging from 480–550 °C (900–1,020 °F) liberates the hydrocarbons.2
* Underground (In Situ): Because rock is a natural insulator, this is a slower process occurring at lower temperatures, roughly 325–400 °C (620–750 °F), which often results in a lighter oil and a higher gas-to-oil ratio.2

Beyond hydrocarbons, this thermal breakdown also releases nitrogen, sulfur, and oxygen compounds.2