Organic petrology and Rock-Eval characteristics in selected surficial samples of the Tertiary Formation, South Sumatra Basin

M. H. Hermiyanto, N. Sudini Ningrum


Organic petrologic data of the DOM of Talangakar and Muaraenim Formations show that the organic matter consisting mainly of vitrinite group is essentially composed of telocollinite (1.0 – 70.8 %) and desmocollinite (0.8 – 66.6 %) with minor telinite (0.6 – 9.4 %), detrovitrinite (0.6 – 6.0 %), and cor- pocollinite (0.6 – 2.0 %). Minor exinite (0.4 – 7.8 %) and inertinite (0.4 – 8.0 %) are also determined. However, mineral matter varies from 0.6 – 99.44 %. Downwards, the increase in vitrinite reflectance (0.33 – 0.48 %) is concomitant with the depth of each formation. Furthermore, based on Rock-eval pyrolysis, TOC value of the Talangakar Formation ranges from 0.09 – 15.38 %, Gumai 0.34 – 0.39 %, Airbenakat 0.32 – 4.82 %, and Muaraenim between 0.08 – 15.22 %. Moreover the PY (Potential Yield) value variation of the Talangakar, Gumai, Airbenakat, and Muaraenim Formations are between 0.04 – 36.61 mg HC/g rock, 0.53 – 0.81 mg HC/g rock, 0.1 – 4.37 mg HC/g rock, and 0.07 – 129.8 mg HC/g rock respectively. Therefore, on the basis of those two parameters, the four formations are included into a gas - oil prone source rock potential. However, the Talangakar and Muaraenim Formations are poor to excellent category, whereas the Air Benakat tends to indicate a poor – fair category and Gumai Formation are only within a poor category. Tmax value of the Talangakar ranges from 237 – 4380 C, Gumai 316 – 3590 C, Airbenakat 398 – 4340 C with exceptions of 4970 C and 5180 C, and Muaraenim Forma- tions 264 – 4250 C. The Talangakar Formation contains kerogen Type II dan III, with the HI (Hydrogen Index) value varies from 45.16 – 365.43. However two samples show value of 0. The organic content of the Gumai and Air Benakat Formations are included into kerogen type III, with HI value ranges from11.87 – 40.82, and 19 – 114 respectively. Moreover the Muaraenim Formation has two category of kerogen type and HI value, those are type III with the HI value of 1 and kerogen type I with HI value of 821.29. The diagram of Tmax vs HI shows that the organic thermal maturation of the four formations are included into an immature to mature level.




organic petrology; rock-eval pyrolisis; organic matter; South Sumatra Basin


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