What happens to kerogen when it is heated for long periods in source rock?

When kerogen is heated over long periods within a source rock, it undergoes thermal degradation and cracking, a process that breaks down heavy molecules into lighter ones.1

Within the oil window—typically occurring at temperatures between 65 °C and 150 °C—this heating causes the kerogen molecules to crack and release attached paraffin chains. Assisted by the catalytic effects of clay minerals, this process produces soluble bitumen compounds, which eventually transform into the various saturated and unsaturated hydrocarbons and asphaltenes that constitute crude oil.1

As temperatures increase further at greater depths, the process shifts. Once the environment exceeds the stability range for crude oil, the remaining kerogen becomes condensed and chemically stable, resulting in the production of dry thermal methane gas as the primary hydrocarbon product.1