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Sand Distribution Pattern and Depositional Model of Kopili Formation (Eocene) with Special Reference to Sequence Stratigraphic Framework from North Assam Shelf, Assam-Arakan Basin, India

Roy Moulik, Sujit 1; Singh, Harvinderjeet 1; Rawat, Ramakrishna 1; Akhtar, Samin 1; Mayor, Sanjive 1; Asthana, Manoj 1
1 ONGC, Dehradun, India.

This study has incorporated enhanced quality 3D data (PSTM/PSDM) along with high resolution biostratigraphic and available G&G inputs to bring out the sand distribution pattern and building up a depositional model within sequence stratigraphic framework of Late part of Middle Eocene to Late Eocene Kopili Formation for better understanding of the reservoir distribution for the entire North Assam Shelf.

Sequence stratigraphy has an important built-in interpretation component, which addresses issues such as the reconstruction of the allogenic controls at the time of sedimentation, and predictions of facies architecture in yet unexplored areas.It is a process response model and thus leading to the interpretation of paleoenvironments which are much more critical for sequence stratigraphy than for lithostratigraphy.As a result, now-a-days sequence stratigraphic concept is being used world over in place of lithostraigraphic concept, in particular, to bring out the facies distribution pattern and depositional model in basinal scale analysis.

The North Assam Shelf is in the mature stage of exploration for relatively shallower horizons and has established oil province from Neogene (Oligocene & Miocene) age. A good no. of wells has been drilled through deeper sections(Eocene & Paleocene) and has established leads from Paleogene age.

Kopili Formation (Middle to Late Eocene) of North Assam Shelf could be further sub-divided into three higher order sequences viz. Seq.-I, II, and III primarily based on logs and available bio-stratigraphic & paleobathymetric data as the seismic imaging is found to very poor within Kopili section. Seq.-I is the bottommost sequence; Seq.-III is the topmost sequence whereas Seq.-II is the intermediate sequence identified within Kopili Formation. Two types of system tracts viz: TST(Transgressive System Tract) & HST(High stand System Tract) are found to be present in each sequence. System tract analysis has brought out facies distribution pattern and barrier bar- lagoon-tidal inlet-tidal bar-bay head delta depositional model has been envisaged for Kopili Formation in the entire north Assam shelf. This model will certainly give a Philip in proper planning for exploration of Kopili Formation in North Assam Shelf.

 

AAPG Search and Discovery Article #90090©2009 AAPG Annual Convention and Exhibition, Denver, Colorado, June 7-10, 2009