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The AAPG/Datapages Combined Publications Database

Indonesian Petroleum Association

Abstract


20th Annual Convention Proceedings (Volume 1), 1991
Pages 621-635

Porphyrins in Extracts as Indicators of Maturity and Depositional Environment of Tertiary Source Rocks from Central Sumatra

P. Sundararaman, S. C. Teerman

Abstract

The Tertiary lacustrine Pematang Brown Shale is a major source of oils in Central Sumatra. In addition to the Brown Shale, the overlying marine Sihapas group, and the Petani Formation may be secondary sources for oil in Central Sumatra. The Telisa sediments, which are part of the Sihapas group, were deposited in a shallow to open marine environment and the Petani was deposited in a marginal marine to brackish environment. Evaluation of the thermal maturity and depositional conditions of the Telisa and Petani sediments are important for evaluating their source potential.

This study focuses on the use of porphyrins in determining the thermal maturity and depositional environment of the Tertiary source rocks from Central Sumatra.

The relative proportion of nickel and vanadyl porphyrins in oils and bitumens is a good indicator of depositional environment of the source rock. Sediments deposited in an marine anoxic environment are dominated by vanadyl porphyrins, whereas sediments deposited in a marine suboxic environment are dominated by nickel porphyrins. The marine Telisa and Petani Formation contain predominantly nickel porphyrins indicating deposition in a suboxic marine environment similar to the Mowry Shale, Wyoming, USA. This is in agreement with the sedimentological, microscopic and other geochemical data. The Porphyrin Maturity Parameter (PMP) has been shown to be an excellent indicator of the maturity of oils and source rocks. The Porphyrin Maturity Parameter (PMP) of the Telisa and the Petani Formations in many parts of Central Sumatra indicates that these units are immature to marginally mature. However, the Telisa Formation is thermally mature and in the oil window in certain parts of Central Sumatra.


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