Lacustrin Potential South Sumatra.pdf

IPA18-348-G

PROCEEDINGS, INDONESIAN PETROLEUM ASSOCIATION Forty-Second Annual Convention & Exhibition, May 2018 LACUSTRINE SOURCE ROCK POTENTIAL IN JANTUNG GRABEN, SOUTH PALEMBANG SUB BASIN, SOUTH SUMATRA Bayu Sapta Fitriana* Mohamad Fery Mustofa* Bimo Ario Putra**

ABSTRACT Source rock kerogen in many proven kitchen in South Sumatra basin mostly known as type II/III which deposited in fluvio-deltaic environments. Jantung sub-basin is one of the graben at OK block which geochemically indicated lacustrine environment. Source rock data from JAG-1 well shows kerogen type I/II from shale in Talang Akar (TAF) and Lahat formation (LAF). This kind of kerogen generally deposited in lacustrine to marine environment. The presences of lacustrine source rock in this area become interesting since lack of hydrocarbon discovered from this type of source rock. Shale samples from TAF and LAF analyzed with TOC (Total Organic Carbon) determination, Rockeval pyrolisis, Vitrinite Reflectance (Ro), and Bitumen extraction analytical techniques. These analysis resulted that TAF and LAF shale have good to excellent source rock potential, with TOC value 2.0 – 6.0 wt%; and indicate lacustrine to marine environment (Kerogen type I/II) as shown by Hydrogen Index (HI) values 699 – 797 (mg/gTOC) in TAF, and 440 – 1,325 (mg/gTOC) in LAF. Bitumen extract from LAF shale also indicated highly anoxic source rock environment with Pristane/Phytane value=1.3 and Prystane/nC17=3. Tmax value 434-438 deg C in LAF shale has entered the early mature phase, which mean maturity at the basin depocenter can be more mature. The mature source rock also confirmed by 1D basin modeling that resulted peak mature stage in LAF with Ro 0.65-0.85. Good to very good hydrocarbon show in reservoir indicate the hydrocarbon already migrated into reservoir, although well testing result doesn’t give good

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JOB Pertamina-Jadestone (OK) Ltd. Freelance Geologist

result. This give indication that hydrocarbon was just passing through reservoir. The absences of lacustrine hydrocarbon type in relationship with mature kitchen can be explained by pathways of migrated hydrocarbon from orthogonal map at migration time. The migration was occur before trapping development. This result encouraged the exploration for stratigraphic trap around Jantung sub basin.