Gumai Shales of Jabung area: Potential source rocks in Jambi Sub-basin and their contributions to the new petroleum system*

Lambok P. Marpaung1, I Nyoman Suta1, Awang H. Satyana2

1PetroChina International Jabung Ltd., 2BPMIGAS

ABSTRACT

Jabung area has been proven as prolific hydrocarbon producer. It is well known that oils and gas have been sourced from terrestrial to fluvio-deltaic shales and coals of Talang Akar Formation. In addition to this, based on geochemical and geologic data, shales of Gumai Formation display characteristics and capability of both potential and generating source rocks. Source potential of Gumai shales is indicated by TOC value of 0.79-8.00 %, potential yield of 0.3-24.83 mg HC/g TOC and T-max of 426-445 oC. Kerogen type II and III predominate the Gumai source shales. Biomarker parameters show that the shales were deposited in anoxic to suboxic environment, indicating a good preservation of organic materials. Geologic setting determines that the Gumai shales were deposited in more marine setting than those of the Lower Talang Akar. However, inputs from higher land plants still influence the source facies. Available maturation data and modeling from well located in the kitchen area reveals that the Gumai source section is within immature to early mature window. Hence, the Gumai source from the existing data analysis is basically the potential source rocks. However, some oils in Jabung area show close correlation to the Gumai shales, showing that the shales have been generating oils. Knowledge of Gumai as both potential and generating source rocks will create new petroleum systems of Gumai shales-Gumai sands (.) or Gumai shales-Air Benakat sands (.). These systems will make migration routes from source to reservoirs to be much simpler. The new petroleum systems will significantly influence the future exploration strategy in the Jabung area.

* Proceedings PIT IAGI Riau 2006, The 35th IAGI Annual Convention and Exhibition, Pekanbaru – Riau, 21-22 November 2006