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ABSTRACT: Sequence stratigraphic framework of Neogene sediments of offshore Bengal Basin, India

Das, S. K., S. Bag, P. Bagchi, T. K. Datta, and D. Biswas , Oil & Natural Gas Corporation Ltd, Calcutta, India

Eocene carbonate build-ups and fault entrapment associated with growth features of Neogene sequence were the prime prospects during the last two decades of hydrocarbon exploration in offshore Bengal Basin. Analysis of 6500 line kilometers of 24 fold 2D seismic data led to the drilling of seven deep exploratory wells without any success. Sequence stratigraphic analysis of all these geoscientific data has brought out a series of hitherto, unexplored interesting stratigraphic plays in the present study.

This study documents the effect of relative sea-level fluctuation and concurrent sediment yield on facies architecture and sequence stratigraphy. The Neogene delta complex was fed primarily by north-south flowing Proto-Ganga-Brahmaputra river system. In addition, the contribution of east-west flowing cratonic paleo-drainage systems, including some major distributory channels of Proto-Mahanadi in the southern part has also been illustrated. The identified prospective stratigraphic plays include basin floor fan, slope fan, lowstand wedge, channel fill sediments and forced regression package within lowstand systems tract and shingled turbidities, discrete lobes of complex sigmoid-oblique progradational package and unconformity related traps within highstand systems tract. The transgressive shale overlying the lowstand deposits and finer clastics surrounding sandy lobes on the slope within highstand sediments may act as a cap. The geochemical analysis suggests that Miocene sediments would be within oil-window zone towards the south-eastern part of deep basin enhancing the prospectivity of these stratigraphic plays.

AAPG Search and Discovery Article #90913©2000 AAPG International Conference and Exhibition, Bali, Indonesia