Assessment of the Hydrocarbon Potential of Cenozoic Basins Offshore Vietnam

Lars H. Nielsen¹, Michael B. Fyhn², Phan T. Dien³, Le C. Mai³, Nguyen T. Dau³, Luong T. Huyen⁴, Nguyen T. Huyen³, Nguyen A. Duc³, Le D. Thang³, Henrik I. Petersen¹, Anders Mathiesen¹, Lars O. Boldreel², Jørgen A. Bojesen-Koefoed¹, Tran T. Nhan⁵, Hans P. Nytoft¹, and Ioannis Abatzis^1
1Stratigraphy, Geological Survey of Denmark and Greenland, Copenhagen, Denmark
²Department of Geography and Geology, University of Copenhagen, Copenhagen, Denmark
³Vietnam Petroleum Institute, PetroVietnam, Hanoi, Viet Nam
⁴Hanoi University of Mining and Geology, Hanoi, Viet Nam
⁵Hanoi University of Science, Hanoi, Viet Nam

A team of Vietnamese and Danish geoscientists and students is studying the petroleum potential of the Cenozoic basins offshore Vietnam. The focus is on generating research results relevant for an assessment of the petroleum potential of the Song Hong, Phu Khanh and Malay-Tho Cu basins, which is less recognised than the proven potential of the Nam Con Son and Cuu Long basins. Collision of India and Eurasia, rotation of Indochina, major strike-slip movements and opening of the South China Sea generated the basins, which contain faulted basement blocks, syn-rift prisms of alluvial sandstones, lacustrine mudstones and coals overlain by post-rift successions of shallow-deep marine clastics and carbonates. Analysis of outcrops and 500m of continuous cores (ENRECA-1 well) from an onshore Miocene rift-sequence has established a predictive model for narrow continental rift-sequences with excellent oil-prone lacustrine mudstones and carrier beds and reservoirs of fluvial sandstones. The model is applicable for parts of the Malay-Tho Chu Basin. The team has further undertaken biomarker analyses of Cuu Long, Song Hong and Malay-Tho Chu oils that indicate an origin from Oligocene lacustrine mudstones similar to excellent oil-prone source rocks known from onshore outcrops and shallow wells. Interpretations of onshore seep oils have encouraged exploration activities in the undrilled Phu Khanh Basin. The team is currently interpreting new seismic data offshore southern Vietnam in the light of new results from structural field work on small inversion structures with Paleozoic-Mesozoic rocks and sedimentological studies of 500m of cores from the Lower Cretaceous (ENRECA-2 well). The outcome of these efforts is expected to generate a better understanding of the pre-rift Mesozoic basin development and the petroleum potential in the region.

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