Figure 1. Some examples of organic compounds in petroleum (schematic), from the simplest (methane) to the most complex (asphaltene). Pyrolysis gas-chromatography of kerogen, the precursor of petroleum in source rocks, directly translates to petroleum composition and properties and is used for predictions ahead of drilling.
Every molecule of oil has methane released with it. This is fossil fuels. It is all organic because the dead dinosaurs and their lagoons were all living and organic.
Petroleum source rocks (click here) can be formed in a variety of depositional environments. Key controls are organic matter production and preservation in the sediment. The organic matter deposited can be of algal, bacterial, or planktonic origin, or stem from terrestrial land plants. In any case, preserved organic matter assemblages can be variable in source rock sequences, depending on input and preservation conditions. Figure 2 shows the macroscopic lithologic variability observed in the Jurassic Posidonia shale, and indicates variability in depositional environment and diagenetic overprint, which in turn can result in organofacies variability. The first step in source rock assessment is thus the detailed investigation of organic facies using pyrolysis techniques....
