PHAN TRUNG DIEN¹ and CLAUS ANDERSEN^2
1Vietnam Petroleum Institute (VPI), and Petrovietnam (PV), Hanoi, Vietnam
²Geological Survey of Denmark and Greenland (DGU), Copenhagen, Denmark

Abstract: Basin Analysis and Petroleum Systems of the SongHong Basin (Vietnam)

SongHong Basin is a structurally complicated Tertiary basin located on the northwest margin of the East Vietnam Sea. The more than 800 km long elongated basin can be subdivided into a number of separate provinces.

The Northeastern part, in the Gulf of Tonking is characterized by a system of narrow Oligocene half-grabens delineated by NE-SW faults. Post-rift Miocene high-destructive deltaic clastics onlap the older formations. Oil-prone Oligocene syn-rift lacustrine shales may be source rocks (type I and II) of fractured Paleozoic carbonate reservoirs on basement horsts.

The Central part, delineated by two major bounding NW-SE fault systems, extends southwards from the Red River Fault Zone into the main Central depocentre, where more than 15 km of Cenozoic sediments accumulated. Oligocene sediments are widespread and are overlain by thick Miocene successions dominated by high-constructive deltaic clastics. Late Miocene compressional movements have created a large number of anticlines and flower structures. The petroleum system consists of deltaic source rocks (type III) charging Oligocene-Miocene clastics in structural traps.

The South part is controlled by longitudinal fault systems, which have created a number of parallel graben structures separated by basement horsts. The Oligocene grabens are filled by tidal lacustrine fine-grained clastics, while the post-rift sagging phase are dominated by Miocene neritic clastics, and platform and reef carbonates on highs. The petroleum systems are presented by both Oligocene lacustrine shales and Miocene marine source rocks. Reservoirs are Miocene build-up carbonates, fractured Pre-Cenozoic rocks on basement highs, and Tertiary clastics.

A large basin-wide regional unconformity is dated to 5.5 Ma. The Pliocene and Quaternary sediments above are virtually non-deformed. However, locally there is evidence of volcanic and mud diapirism in the south.

AAPG Search and Discovery Article #90928©1999 AAPG Annual Convention, San Antonio, Texas