Effect of artificial maturation on carbazole distributions, as revealed by the hydrous pyrolysis of an organic-sulphur-rich source rock (Ghareb Formation, Jordan)

Hydrous pyrolysis experiments were performed on the Ghareb Formation (Upper Cretaceous, Jordan), a carbonate- and organic-rich (TOC 19.6%) source rock, using a temperature range of 200 to 360 degrees C (72 h). The original sediment contains only low amounts of carbazoles, (maximum 2.2 mu g/g bitumen for 1-methylcarbazole). With increasing thermal maturation, intense generation begins at temperatures only in excess of 300 degrees C, reaching a maximum at 360 degrees C. Likewise, during natural maturation, generation occurs at later stages of maturity (e.g. for Tithonian source rocks at > 0.81% R-r and for Posidonia Shale at >0.88% R-r). Some isomeric changes during hydrous pyrolysis do not resemble those in nature whereas others do. The relative abundances of selected C-1- and C-2-alkylcarbazoles on ternary diagrams reveal differences, whereas the benzo[a]carbazole/benzo [a]carbazole + benzo [c]carbazole ratio is closely similar. The latter result supports the contention that maturation plays a key role in controlling carbazole distributions in source rocks. However, the results for alkylcarbazoles, especially the C-2-carbazoles, are not easy to interpret. (C) 1998 Elsevier Science Ltd. All rights reserved.