Steranes and terpanes in kerogen pyrolysis for correlation of oils and source rocks

Comparison of biological marker alkanes in the kerogen pyrolyzate and bitumen from a sediment is a useful test for the indigenous nature of sediment extracts. For the pyrolysis conditions used, the bulk of the hydrocarbons is released from the kerogen matrix between 375° and 550°C; and its steriochemistry is almost the same as that observed in the extractable bitumen in a genuine source rock. Examples are given to demonstrate that, during pyrolysis, the sterane/terpane ratio decreases and secondary terpanes are generated at the expense of primary ones.The mechanism of artificial petroleum generation by pyrolysis differs from ‘natural’ diagenesis during geological time and is reflected in the composition of certain C₂₇-C₂₉ steranes, as demonstrated by simulation experiments and C₂₉-C₃₀ moretanes and hopanes. The $\text{5α}\text{5β}$-sterane ratios, jointly with $\text{17α(H)-hopane}\text{17β(H)-moretane}$ ratios, tricyclic terpane concentrations and $\text{17α(H)}\text{17β(H)}$-trisnorhopane ratios, allow the differentiation of kerogens from adjacent stratigraphies.