Publications

Most of the Tertiary basins of Southeast Asia share a geological history that comprises early Tertiary graben formation, fill and transgression, followed by periods of marine transgression in the Early to Middle Miocene and a phase of regressive deltaic progradation in the Late Tertiary. Geological variation within the basins, however, is considerable and is of very short wavelength. This is reflected in the prospectivity, which also varies considerably and is extremely hard to predict in detail.Charge is one of the most dominant elements determining prospectivity, and it can be applied directly via the typical hydrocarbons and source rocks identified to the definition of the characteristic petroleum systems or hydrocarbon habitats developed in the area. These are:(i) Early synrift lacustrine hydrocarbon system (Oligocene to Early Miocene), oil prone.(ii) Late synrift transgressive deltaic hydrocarbon system (Oligocene to Early Miocene), oil and gas prone.(iii) Early postrift marine hydrocarbon system (Early to mid Miocene transgression), mainly gas prone.(iv) Late postrift regressive deltaic hydrocarbon system (mid Miocene to Pliocene), oil and gas prone.Lacustrine shales, fluvio-deltaic coals/coaly shales and organic-rich marine shales have been shown to have generated the characteristic light waxy oils and abundant gas of the region, and the gross subdivision presented above results in large part from the sequence and distribution of source rock depositional environments in the basins.Examples of oil and source rock occurrence as well as geochemical analyses from basins in various parts of Southeast Asia, which illustrate the principle of this gross hydrocarbon or petroleum system division, are discussed and placed in their tectono-stratigraphic context. It is concluded that in a broad sense, more proximal basins (those closer to the Sunda continental platform area) and sedimentary environments tend to be more oil prone, more distal basins and environments tend to have more gas potential, while intermediate basins and environments are both oil and gas prone.