ORGANIC GEOCHEMICAL STUDY OF SOURCE ROCKS AND THEIR CORRELATION WITH PETROLEUM IN THE MALIANA BASIN OF TIMOR-LESTE

• Main Author: Pires, Joanico
• Format: Theses
• Language: Indonesia
• Subjects: Geologi, hidrologi & meteorologi
• Online Access: https://digilib.itb.ac.id/gdl/view/80918
• Institution: Institut Teknologi Bandung

Varying ancient environmental conditions greatly influence the geochemical characteristics of oil and gas; Therefore, knowing the origin and characteristics of petroleum and gas formed from source rocks is one way to understand the petroleum system. The research area is located in the Bobonaro area, Maliana Basin, in the onshore area of Timor-Leste. The research subject is the characterization of petroleum and source rocks. The objects include general regional geological conditions such as tectonics, structure, stratigraphy with special discussion about organic geochemical characters, namely sedimentary rock richness, maturity, and type, as well as the distribution of biomarkers that can be used to interpret the origin of organic material, depositional environment, and type of organic material. Apart from objects in the form of rocks, samples of crude oils were also taken which were analyzed for biomarker content so that they could be correlated with sedimentary rocks to determine the presence/absence of the potential for sedimentary rocks in the research area to become petroleum source rocks. Source richness analysis carried out on two members of the Babulu Formation (Clastic Member and Shale Member) shows that this formation has fair to good richness with TOC values between 1% and 12%. The organic material content for the Aitutu Formation (Carbonate Member and Shale Member) is between 1% and 5%, and the Viqueque Formation contains TOC between 0.50% and 2%. Maturity analysis carried out on the kerogen contained in the Babulu and Aitutu Formations shows that these two formations are relatively mature, while the Viqueque Formation is still in an immature stage. Analysis of kerogen types which was also carried out on the Babulu and Aitutu Formations generally leads to gas-producing type III kerogen, but there are also those originating from type 1 kerogen and a mixture of types II and III, which can form petroleum and gas when mature. The distribution of sterane biomarkers from m/z 217 for both rock and petroleum samples shows a relatively high abundance of diasterane. The dominant composition of C27 and C29 steranes is always balanced in all samples, indicating that the supply of organic material in petroleum and source rock samples is thought to come from a mixture of algae and higher plants deposited in a transitional marine environment. Triterpane biomarkers, analyzed from fragmentogram m/z 191) do not show an abundance of higher plant supplies, such as bicadinanes, which indicate organic matter comes from higher terrestrial plants deposited in the marine environment. Two crude oil samples taken from the Pualaka and Suai Loro areas are thought to have organic material originating from algae deposited in a transitional marine environment. All rock sample maturity indicators from the results of saturated and aromatic biomarker analysis show that all samples are in the immature to mature zone, which is parallel with those results from kerogen analyses. The Pualaka and Suai Loro petroleum samples show the maturity of the saturated and aromatic hydrocarbon fraction biomarkers indicating that the samples are in the mature zone. Carbon isotope analysis of seven outcrop samples from the Babulu and Aitutu Formations shows that the the sediments contain hydrocarbons with most of the organic material originating from marine biota, which is most likely related to the delta depositional environment.