Why can heating oil shale underground take months or years?

Heating oil shale underground via in situ processing is a slow process, often requiring months or years to complete, primarily because rock is an excellent insulator.1

Unlike surface retorting, which allows for rapid heating in specialized vessels, underground methods must heat large volumes of rock in place. Because the surrounding geological formation resists the transfer of heat, the process must be conducted gradually to effectively pyrolyze the kerogen macromolecules. This slow heating occurs at lower temperatures—typically between 325 and 400 °C—compared to the higher temperatures used in surface retorts. While this extended timeframe is a significant challenge for in situ production, it results in the generation of a lighter oil and a higher gas-to-oil ratio.21