GEOCHEMICAL CHARACTERISTICS OF OIL SEEPAGES FROM DAM THI NAI, CENTRAL VIETNAM: IMPLICATIONS FOR HYDROCARBON EXPLORATION IN THE OFFSHORE PHU KHANH BASIN

J. A. Bojesen-Koefoed^*1, L. H. Nielsen¹, H. P. Nytoft¹, H. I. Petersen¹, Nguyen Thi Dau², Le Van Hien², Nguyen Anh Duc² and Nguyen Huy Quy²

¹Geological Survey of Denmark and Greenland (GEUS), 10 Øster Voldgade, DK-1350K Copenhagen, Denmark.

²Vietnam Petroleum Institute (VPI), Trung Kinh Street, Yen Hoa, Cau Giay, Hanoi, Vietnam.

^* author for correspondence, e-mail jbk@geus.dk

Seepage oils are found in varying degrees of biodegradation and modes of occurrence at different locations in the embayment. Thus, oil was observed to fill fractures in freshly quarried outcrops of Cretaceous granite, and also occurs in shallow pits dug in the beach sand and in shallow basins used for shrimp farming. The oils indicate active seepage from kitchen areas or leaking accumulations in the Phu Khanh Basin. Seismic data suggest the existence of both source rocks and kitchens, and indicate a possible migration route from the deep basin to the surface at the bay. A few samples show anomalous compositions, indicating the presence of two other oil types which have different sources. These occurrences cannot at present be explained. However, the results obtained are encouraging for future exploration in the Phu Khanh Basin.

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