Abstract: Nam Con Son Basin

Nguyen Trong Tin, Nguyen Dinh Ty, Luu Thanh Hung

The Nam Con Son basin is the largest oil and gas bearing basin in Vietnam, and has a number of producing fields. The history of studies in the basin can be divided into four periods: Pre-1975, 1976-1980, 1981-1989, and 1990-present. A number of oil companies have carried out geological and geophysical studies and conducted drilling activities in the basin. These include ONGC, Enterprise Oil, BP, Shell, Petro-Canada, IPL, Lasmo, etc.

Pre-Tertiary formations comprise quartz diorites, granodiorites, and metamorphic rocks of Mesozoic age. Cenozoic rocks include those of the Cau Formation (Oligocene and older) Dua Formation (lower Miocene), Thong-Mang Cau Formation (middle Miocene), Nam Con Son Formation? (upper Miocene) and Bien Dong Formation (Pliocene-Quaternary). The basement is composed of pre-Cenozoic formations.

Three fault systems are evident in the basin: north-south fault system, northeast-southwest fault system, and east-west fault system. Four tectonic zones can also be distinguished: western differentiated zone, northern differentiated zone, Dua-Natuna high zone, and eastern trough zone.

Well-distributed Oligocene claystones bearing Type II and Type III kerogens form good source rocks. Reservoir rocks include the fractured pre-Cenozoic basement, Paleogene quartzose sandstones (12%-16% porosity), and lower Miocene quartzose sandstones (18%-25% porosity). Several caprocks are recognized. These include the 100-m- to 400-m-thick Oligocene argillite claystone caprock of the Cau Formation, the Miocene shale\silt caprock, which constitutes a localized seal, and the middle Miocene shale regional caprock.

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