The Far East Hydrocarbon Habitat: The Charge Perspective

Abstract

From a hydrocarbon exploration point of view, the Far East is typically the realm of Tertiary basins with youthful prospects. Nearly all of the oil and gas in these basins is terrestrial in origin and the current cycle of tectonic development began in late Mesozoic-early Tertiary history during which much of what is now east and southeast Asia consisted of a large land area comprised of microcontinental blocks welded together by fold belts. In the Paleogene, this continental area was subjected to back-arc extension and collapse as a consequence of complex plate readjustments. Subsidence took place in fault-bounded (graben) depressions throughout the area and widespread lacustrine environments were established. The middle to late Tertiary history of these basins was dictated by their proximity to the open ocean and by the extent of crustal subsidence, but follows a transgressive-regressive cycle that gives rise to the following groups of plays: (1) early Tertiary transgressive clastics, basically oil prone, (2) Miocene carbonates of the maximum transgression, gas prone, and (3) late Tertiary regressive clastics, oil and gas prone. The mechanisms of generation and migration in Far East Tertiary basins were poorly understood and the type and volumes of hydrocarbons trapped often appear tomore » be unpredictable. At present, three basic depositional realms are envisaged for source rock accumulation: (1) lacustrine grabens ([open quotes]deep lakes[close quotes]) that contain rich algal-SOM type I-II source rocks and are oil prone, (2) paralic coal and coaly shale swamps, developed in a variety of onshore deltaic environments; charge from these source rocks is variable, and (3) coastal and marine, especially related to deltas where terrestrial organic material is introduced, accumulates, and is bacterially degraded and preserved. The distribution and types of hydrocarbons produced from these source rocks and their relations to hydrocarbon habitat are reviewed.« less