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ABSTRACT: Depositional environment and petroleum habitat of cretaceous reservoirs in southern Nagapattinam sub-basin, Cauvery Basin, India

Prabhakaran, S. and N. Ganesh , Oil And Natural Gas Corporation Ltd, Chennai, Tamilnadu, India

Hydrocarbon occurrences in southern part of Nagapattinam basin are within Palk Bay Formation (Turonian and older) and Nannilam Formation (Santonian to Maastrichtian). Contrasting style of provenance, sand dispersal and tectonics are discussed, for these two formations.

In contrast to earlier models, it is established that the Palk Bay Formation sediments are attributed to have been dispersed from Srilankan-Vedaranyam massif from South, Southwest and reservoir sands were deposited in a shallow marine environment as coastal beaches, beach dune/bar and tidal channels during Cenomanian transgression which covered from North to South.

Consequent upon a regional tilt Nannilam Formation was deposited from a Westerly provenance. The reservoirs are within wave dominated delta comprising of transgressive bars and tidal channels. Basinal tilt is envisaged to be towards North during Palk Bay Formation and East during Nannilam Formation which is a shift from the earlier concept of gradual easterly tilt.

Hydrocarbon entrapment in Palk Bay Formation is observed to be strati-structural and diagenetic, with bigger pools in north and smaller pools in South, whereas in Nannliam Formation accumulation is structural with smaller pools to the North. The prospective reservoirs are within Palk Bay Formation in Northwest to Southeasterly elongation with narrow width.

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