Abstract: Some Cenozoic Hydrocarbon Basins on the Continental Shelf of Vietnam

Phan Trung Dien

Sedimentary basins on the continental shelf of Vietnam are characterized by riftings, spreadings, and saggings under which the East Vietnam Sea was formed. They are also the sites of almost all of the commercial hydrocarbons of Vietnam. The formation of these basins was related to different geodynamic processes.

(1) The pre-Oligocene basement consists of igneous, metamorphic, and metasediment complexes. The Cretaceous-Eocene basement formations are formed by convergence of continents after destruction of the Tethys Ocean. Many Jurassic-Eocene fractured magmatic highs of the Cuulong basin basement constitute important reservoirs that are producing good crude oil. The Paleocene-Eocene formations are characterized by intramountain metamolasses, sometimes interbedded Volcanic rocks.

(2) Interior structures of the Tertiary basins connect with rifted branches of the widened East Vietnam Sea. Different petroleum plays exist in these basins, which were filled with Oligocene-Miocene sediments.

Bacbo (Song Hong) basin is predominated by alluvial-rhythmic clastics in high-constructive deltas, which developed on the rifting and sagging structures of the continental branch. Petroleum plays are constituted from type III source rocks, clastic reservoirs, and local caprocks.

Cuulong basin represents sagging structures and is predominated by fine clastics, with tidal-lagoonal fine sandstone and shalestone in high-destructive deltas that are rich in type II source rocks. The association of the pre-Cenozoic fractured basement reservoirs and the Oligocene-Miocene clastic reservoir sequences with the Oligocene source rocks and the good caprocks is frequently met in petroleum plays of this basin.

Nan Conson basin was formed from complicated structures that are related to spreading of the oceanic branch. This basin is characterized by Oligocene epicontinental fine clastics and Miocene marine carbonates that are rich in types I, II, and III organic matter. There are both pre-Cenozoic fractured basement reservoirs, Miocene buildup carbonate reservoir rocks and Oligocene-Miocene clastic reservoir sequences, in this basin.

(3) Pliocene-Quaternary sediments are sand and mud carbonates in the shelf facies of the East Vietnam Sea back-arc basin. Their great thickness provides good conditions for maturation and trapping.

AAPG Search and Discovery Article #90982©1994 AAPG International Conference and Exhibition, Kuala Lumpur, Malaysia, August 21-24, 1994