--> Abstract: Oil and Gas Distribution in SE Asia-Australasia, by J. V. C. Howes; #90937 (1998).

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Abstract: Oil and Gas Distribution in SE Asia-Australasia

HOWES, J.V.C. Atlantic Richfield Indonesia, Inc.

The distribution of significant oil and gas volumes in SE Asia-Australasia is highly concentrated in just a few chronostratigraphic units, with Paleogene source rocks accounting for over 50% of the region's petroleum resources, and overlying Neogene sandstones providing the predominant reservoir. The majority of Tertiary production comes from SE Asia, with Mesozoic and Paleozoic production concentrated in Australia and New Guinea.

Total reserves discovered to date in SE Asia-Australasia are over 130 billion barrels of oil equivalent, of which 65% is gas. More than 2,000 separate oil and gas fields have been discovered in eleven countries. There are at least 50 giant oil and gas fields and 100 productive petroleum systems in the region. The geologic age of source rocks, reservoirs and seals spans 500 million years from the Paleozoic to the Pliocene.

Key elements of the region's petroleum systems have been fundamentally controlled by global tectonic events and lithospheric plate interaction. There is a clear division of source rock type and age between those systems located on the Eurasian lithospheric plate and those on the Indo-Australian plate.

The majority of Australian-affinity petroleum systems are genetically linked to Late Paleozoic through Mesozoic rifting of the Australian continental margin, which was initiated by the breakup of Gondwanaland. The majority of S.E. Asian petroleum systems formed during the Tertiary and are associated with convergent plate margins or the affects of convergence in the region. Systems in the Philippines and northern New Guinea are related to the more complex oblique interaction of the Philippine Sea and Pacific plates with the Eurasian and Indo-Australian plates.

Source rocks include lacustrine, fluvial-deltaic, marine and marine carbonate facies. Lacustrine sources tend to be strongly oil-prone, marine sources often more gas-prone. Oil-prone fluvio-deltaic coals are particularly significant in some systems, while several shallow systems contain bacterially-generated gas.

Reservoirs range from fluvial-deltaic, paralic, and marine sandstones, through alluvial fans, turbidites, and massive carbonate bioherms, to less conventional fractured volcanics, volcaniclastics, and hydrothermally altered granites. Seals are generally mudstones; evaporites do not play an important role in the region's oil and gas accumulations.

AAPG Search and Discovery Article #90937©1998 AAPG Annual Convention and Exhibition, Salt Lake City, Utah