Publications

Hydrocarbon exploration in the Tarakan Basin indicates that, in general, the eastern part (e.g. Tarakan and Bunyu fields) is more promising than the western area. In order to find more potential area(s), particularly in the western part, a new approach based on an integration study between stratigraphic framework and geochemistry has been conducted to analyse the petroleum system. A sequence stratigraphic framework has been established in the Simenggaris Block with eight sequences of Oligocene to Pliocene age having been identified (SB-1 to SB-8).A geochemical study reveals that shales belonging to SB-1 to SB-8 contain organic carbon (TOC) between 0.65 and 7%, indicating that several are sufficiently rich to be considered hydrocarbon source rocks. Moreover, almost all sequences contain some coals or carbonaceous materials with TOC content up to 70%. In terms of maturity, well data show that only SB-2 and SB-1 (Naintupo Formation and older) have reached optimal maturity to generate hydrocarbons. However, basin modelling results for the deeper areas adjacent to structural highs indicate that SB-5 to SB-3 sequences (Meliat Formation) are in the middle mature stage (around 0.7 to 1% vitrinite reflectance equivalent). Furthermore, peak oil generation in the area was reached between 10 and 1 million years before present. On the basis of their hydrogen index (HI) values, all formations within the SB-1 to SB-2 interval consist of a mixture between type II and type III kerogens (HI 50-454), indicating that they may produce oil and gas.In this study, ten crude oil samples were collected from the study area. Geochemical analyses on these crude oils reveal that they appear to be predominantly generated from the Naintupo Formation of SB-2. However, another formation (i.e. Meliat Formation of SB-5 to SB-3) could also be the source of these oils.