Abstract

Lacustrine rift systems have sourced a large portion of the known hydrocarbon reserves in S.E. Asia, and their importance as exploration targets is well established. Our exploration experience has shown that the source rock quality and maturation are the most important factors controlling the hydrocarbon potential of these basins.

In this paper we describe the rift architectures, depositional sequences, and sedimentary geochemistry of three Palaeogene and one Cretaceous/Palaeogene graben systems in Indonesia, Thailand and China. The graben described are the Bandar Jaya Graben in South Sumatra, Kampar Kanan Graben in Central Sumatra, Phetchabun Graben in Thailand, and Dongting Graben in China. These graben cover a range of rift architectures related to regional extension and wrench tectonic regimes, and represent depositional sequences deposited in oxic to anoxic, freshwater to saline lacustrine environments in deep to shallow water lakes. Climatic conditions range from arid in Dongting to tropical throughout Indonesia and Thailand.

We describe the geochemical characteristics of the source rocks in these graben in context of their depositional systems and characterize their non-marine paleoenvironments. Compositions of oils associated with these graben are controlled by the nature of the source rocks and their stage of thermal maturation. Differences in chemical features, including biomarkers and isotopes, enable oils to be characterized and identified in terms of paleoenvironment.