Depositional Architecture of Mio-Pliocene Sequences in Offshore Bengal Basin

Bengal Basin located along the northeast coast of India has a thick pile of MIO-Pliocene sediments fed by a number of large rivers like Ganga, Brahmaputra, Mahanadi and smaller rivers like Subarnarekha, Baitaram and Brahmani. The basin covers an area of 40,000 sq km in the Bay of Bengal. The sediments in the present day shelf area exhibit a complex deposition history with unique juxtaposition of shallow and deep water sediments in the form of deltas, distributary channels, Pro-Delta sediments and incised canyons, filled up with channel-levee complex deposits.

A detailed study was carried out on the morphology and architecture of the different depositional elements and units utilizing different vintages of 2D/3D seismic and data from drilled wells Geo-Body mapping and attribute studies reveal finer details of the complex system Special seismic attributes such as spectrally decomposed amplitude, waveform classifier and 'sweetness' (amplitude by square ischolar_main of frequency) were quiet helpful in understanding the morphological details of the system. The following depositional elements have been brought out

•Delta-Distributary channel complex associated with incised valley and tidal inlets.

•Shelfal Canyon cut and fill sequences.

o Simple canyon fills Simple "V" shaped cuts with fills in the form of low to moderate sinuous.

channels.

o Complex Canyon cut and fills Numerous, repeated canyon cuts caused by Mass-Wasting with intervening fills in the form of deep water to Sub-Aerial channels and deltaic progradational deposits.

•Deep-Water Channel Complex Fed by large canyon up-dip. These depositional elements do not form part of the canyon fill, but occur down-dip.

The sand and si1t lithological distribution in the above depositional complexes form the predominant hydrocarbon reservoir units. The numerous reservoir bodies within the above units of varying lateral and vertical extents, are expected to hold the future exploration potential in this frontier basin.