Oligocene combination/stratigraphic traps and their reservoir quality in Cuu Long basin, offshore Vietnam

Abstract

Cuu Long basin is a Cenozoic rift basin located in the Southeastern shelf of Vietnam with high potential of oil and gas. Up to date, most production in the Cuu Long basin is contributed from structural traps, making them more and more depleted after years of exploitation. Exploration activities in the Cuu Long basin, therefore, are shifting towards nonstructural traps including stratigraphic and/or combination ones.

By integrating exploration methods such as seismic sequence stratigraphy and seismic attribute interpretation, petrophysical and petrographical analysis, this article discusses the assessments of combination/stratigraphic trap types within the Oligocene section in the Cuu Long basin, including (i) identification of several trapping mechanisms and (ii) some evaluations of the trap’s reservoir quality utilising the database of some 2D/3D seismic sections, several wells and unpublished reports. The research results show that the key forming factor for primary stratigraphic traps of sand body is lithology change and the one for pinch-out stratigraphic traps is tapering off of sand layers landward or toward the horsts. The reservoir quality of these traps ranges from moderate to good. Further detailed studies on reservoir distribution and sealing capacity of these trap types, however, need to be carried out to fully evaluate hydrocarbon potential of these stratigraphic/combination traps, and minimise risks in exploration drilling.