BICADINANES AND RELATED-COMPOUNDS AS MATURITY INDICATORS FOR OILS ANDSEDIMENTS

Biomarker maturity indices have proven useful in petroleum exploration to assess the thermal maturity of oils and sediments. However, their application to deltaic petroleum systems is often hindered by source a nd diagenetic interferences. Recently, we have described several new m aturity indices based on the catagenetic products of the plant biopoly mer polycadinene. These indices should be largely immune to biochemica l effects during diagenesis, since little microbial activity will rema in at temperatures sufficient to dissociate the polymer.Here we report changes in five polycadinene-related maturity indices through a arine -fluvio-deltaic depositional sequence in the South Sumatra Basin, Indo nesia. The results are compared with the maturity required for oil gen eration as estimated by kinetic modelling and with conventional maturi ty indicators such as sterane epimerisation and the methyl phenanthren e index. The data confirm that the polycadinene indices are less subje ct to source and diagenetic interferences than those based on the ster ane and aromatic hydrocarbon distributions. Values for several of the indices have also been measured for 17 Tertiary oils from Southeast As ia, Papua New Guinea, New Zealand and Australia. Contrary to an earlie r report, the bicadinane maturity indicator (BMI-1) continues to chang e into the oil window and hence may be useful in ranking the relative maturity of oils as well as sediments. The BMI-1 values for two oils h aving unusually low sterane maturities are normal, leading us to quest ion whether the low sterane maturity of many Tertiary-age oils is due to their source rocks having been heated more rapidly than those of ol der oils. Copyright (C) 1996 Elsevier Science Ltd