A study of the composition of light hydrocarbons (C5–C13) from pyrolysis of source rock samples

Pyrolysis–GC (open system) has been performed on a total of 30 source rock samples with quantification of all identified components in the C5–C13 range. Ten samples are from the marine shales of the Upper Jurassic Spekk Formation and 10 samples from the coals and coaly shales of the Lower Jurassic Åre Formation, from offshore Mid-Norway. This sample set was expanded with 10 samples from the Danish sector, i.e. seven samples from the marine shales of the Upper Jurassic Farsund Formation and three coal samples from the Middle Jurassic Bryne Formation. The samples were selected to cover different maturity levels and facies. The light hydrocarbon distribution generated by pyrolysis shows a clear compositional difference between the different source rock types. In general, the Åre and Bryne Formations were relatively enriched in mono-aromatics and naphthalenes, while the Spekk and Farsund Formations were richer in n-alkenes and n-alkanes. Variations in terrestrial influence of the marine shales of the Farsund and Spekk Formation samples were also observed. It is found that the abundance of m+p xylene most effectively distinguishes between the different source rock types. This is verified by multivariate modelling. It is shown that the light hydrocarbon composition generated by pyrolysis of kerogen is more affected by source facies than maturity variations.