DIAGNOSIS CHARACTERISTICS OF UPPER OLIGOCENE STRATIGRAPHIC TRAPS IN SOUTHEASTERN CỬU LONG BASIN

Nguyễn Đình Chúc¹, Nguyễn Đình Minh¹, Nguyễn Xuân Nam²
Đỗ Anh Tuấn¹, Nguyễn Quang Hưng¹, Bùi Văn Cương^3
1PetroVietnam Domestic Exploration and Production Company Ltd; Vietnam Institute of Geosciences and Mineral Resources; ³PetroVietnam Exploration Production Corporation

Abstract: Cửu Long basin is the most important sedimentary basin contributing greatly to Vietnam’s annual petroleum production. The major targets for exploration and production in Cửu Long basin were pre-Cenozoic fractured basements and Cenozoic structural traps of tectonically formed anticlines. Other targets such as stratigraphic/combination traps formed due to stratigraphic/lithologic changes have not been paid sufficient attention in exploration activities; As petroleum resources from reservoirs of traditional types become exhausted after many years of production (the remaining unexplored potential targets do not have sufficient reserves for development and production), exploration activities in Cửu Long basin have been focusing on more complicated types of stratigraphic/combination traps. Recent exploration activities in Southeastern Cửu Long basin identified several stratigraphic/combination traps not only as pinch-outs but also traps formed by appropriate facies changes. This article focuses on diagnosis characteristics and predicting the distribution of recently identified Upper Oligocene stratigraphic traps in Southeastern Cửu Long Basin. Based on seismic stratigraphy sequence point of view, through conjunction of geology, seismic, well-log and sedimentary environment data, the characteristics and the distribution of Upper Oligocene stratigraphic traps in region are revealed. These traps are seismically characterized by medium to high amplitude reflections of sigmoid architecture. Gamma ray response of these traps has funnel shape with abrupt changes in GR values at top boundary. Depositional environments are mainly fluvial or deltaic. These traps have fan-like shapes and are distributed along the eastern slope of Côn Sơn Swell. The oil and gas potential in Upper Oligocene stratigraphic traps are proved not only reserve conventional resources but also unconventional ones.

Keywords: Cửu Long basin, stratigraphic trap, rock facies change, distribution, diagnosis characteristic

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