Sumatra/Java oil families

In areas where substantial oil production has been established, regional crude oil geochemical studies are excellent ways of identifying, evaluating and comparing the various petroleum systems that have contributed to reserves. The number and type of effective source rocks can be determined by establishing the number of compositionally distinct oil families. Inferences regarding source rock depositional environment are possible since the geochemical characteristics of crude oils reveal important information on paleoenvironmental conditions of source rock deposition and possible age. In order to understand better the petroleum systems of Sumatra and Java, 122 crude oil samples (Fig. 1) have been geochemically analysed. The detailed analytical program included measurements of bulk parameters (API Gravity, %S, V and Ni content), stable carbon isotope composition of C15+ hydrocarbon fractions, whole oil gas chromatography, and terpane and sterane biomarker distributions using GC/MS. The analytical data were compared using multivariate statistical techniques such as cluster and principal component analyses (Fig. 2). With this approach, the majority of the oils were divided into two main petroleum systems, ‘lacustrine’ and ‘terrigenous’. Both of these petroleum systems are supplied by Tertiary-aged source rocks. Two oils from the North Sumatra Basin exhibit marine affinities, whilst several oils from Central and South Sumatra exhibit intermediate geochemical characteristics suggestive of mixing. Further detailed examination of each petroleum system, sometimes using more specific geochemical criteria, typically resulted in the establishment of sub-groups of oils according to specific source environment, such as lacustrine fresh versus lacustrine saline. The oil families ‘Lacustrine’ oils ‘Lacustrine’ oils