Abstract

Problems can be encountered in assessing the maturity of petroleum and petroleum source rocks using vitrinite reflectance and conventional biomarker data especially when the source rocks have been subjected to rapid heating and contain abundant land plant remains or when the crude oil has been biodegraded. A new maturity indicator based upon reactions of cadalene, a common constituent of source rocks and crude oils of Tertiary age, has been proposed. This maturity indicator is based on the relative abundances of cadalene and isocadalene and changes in a uniform manner through the oil window and into the more mature zone where condensates form. The proposed maturity indicator has been shown to change in a uniform manner with increase in sample depth in two exploration wells from the South Sumatra Basin. Values of the maturity indicator for a range of crude oils and condensates show that the new parameter has a wide range of values and can be used for immature oils through to very mature condensates. The method is also applicable to biodegraded crude oils.