The Potency of Eocene Shale of Nanggulan Formation as Hydrocarbon Source Rock



In western Indonesia, Eocene shale is generally considered as potential source rock. Nanggulan Formation which is outcropped at Kulonprogo-Yogyakarta consist of shale interval with Eocene in age. The analysis of its organic material content, kerogen type and maturity level are conducted to know its potency. Laboratory analysis of 11 samples were done to measure its TOC (Total Organic Carbon) content. Samples with TOC > 0.5% then were analyzed to measure its VR (Vitrinite Reflectance) and TAI (Thermal Alteration Index). Maturity level also calculated by TTI (Time Temperature Index) from burial history model. The result of analysis shows there are various TOC content and 7 samples of them have good-excellent class (more than 1%). Kerogen type of those samples are tipe III (non fluorescene amorphous-humic kerogen). One sample has good indication of hydrocarbon forming (S1=1.38 & S2=7.62 mg/g). Unfortunately the maturity level of the samples are immature (highest Ro 0.39, Tmax 422oC and TAI 2). Otherwise, TTI calculation result from subsurface burial history model indicates that some area are mature and reached the gas window since 0.4 mya, especially in the area which has influenced by volcanic intrusion at Oligocene (28.5 mya). Therefore Nanggulan Formation shale has potential capacity as source rock with some limitation in maturity level.

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Authors : Sarju Winardi, Budianto Toha, Moh Imron, D. Hendra Amijaya