Publications

The kerogen types at the origin of oil in the Jabung block are predominantly type-II and III based on Rock Eval pyrolysis, and are interpreted to originate from the fluvio-deltaic shale & coal of the Oligocene Talang Akar Formation (TAF). However, several outlying oils have been found in the wells NB-1 & NB-4 of the North Betara Field and indicate that kerogen type-I of lacustrine origin may also be in play. This scenario is further suggested by biomarker and carbon isotope ratios. In this paper, we infer that those oils are sourced from the Eocene Pre-Talang Akar Formation (Pre-TAF) section. This opens new exploration prospectivity for the Jabung area. Our analysis of selected petroleum system elements suggests that the lacustrine oils encountered in NB-1 & NB-4 originate from Eocene Pre-TAF source rock in deeper part and migrated into the younger Oligocene TAF sandstone as a sub-surface leak, or “a subsurface oil seep”. Oil migrated by fault vertically and then spread laterally to fill traps in TAF. A widespread unconformity at top pre-TAF may have provided an excellent seal at the origin a pre-TAF confined petroleum system, prevented the lacustrine oil from entering all the fields/structures in the Jabung block, This could explain the minimal distribution of the lacustrine oil at TAF level and above in the Jabung area. The Pre-TAF is associated with the early syn-rift phase in South Sumatra Basin. It also refers as Lahat or Lemat Formation in the basin and is a widely under-explored play, evidenced by the low reserve magnitude of fewer than 100 MMBOE. The distribution of Pre-TAF as source and reservoir rock is restricted to syn-rift depocenter area. From our latest interpretation, Pre-TAF in NEB Field, observed clearly from the 3D seismic data, is potentially well developed and of good quality, although no wells have penetrated the interval to date