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ABSTRACT: Exploration significance of the recognition of rift graben lacustrine source rocks

Williams, Harold H.1 and Roger T. Eubank2
(1) N/A, Alhambra, AB 
(2) N/A, N/A, Indonesia

The recognition and development of new geologic concepts frequently result in renewed exploration impetus in individual basins, as well as large geographic regions. We believe that the recognition of a lacustrine rift graben source for the oils in Southeast Asia in the early to mid 1970's by geologists of Caltex Pacific Indonesia (CPI) is a classic example of the application of a new geologic concept having significant impact on exploration strategy and exploration impetus.

The widespread marine shales of the Miocene Telisa Formation were generally believed by industry to be the only source. In CPI, acceptance of the concept of a rift graben lacustrine oil source was hampered by the false premise that these Paleogene rift graben were too small to have sourced the large volumes of discovered hydrocarbons.

In this paper we review the development of the concept of the rift graben lacustrine source for the high wax Southeast Asian oils. We use examples from the rift graben of the Central Sumatra Basin to show how the lacustrine source concept developed. We illustrate its subsequent impact on exploration strategy throughout the area with a general overview of the distribution of rift graben in Southeast Asia. Specific basins are discussed to illustrate the impact of the rift graben lacustrine source concept.

Anecdotal stories of the difficulties encountered by the CPI explorationists developing the concept are included. We hope to encourage other explorationists to persist in developing new concepts and overcome old, ingrained perceptions.

AAPG Search and Discovery Article #90913©2000 AAPG International Conference and Exhibition, Bali, Indonesia