Tectono-Sedimentation and Hydrocarbon Prospectivity of Paleogene Sediments in Dhansiri Valley, A&AA Basin, India

Ram K. Singh, Pratim Bhaumik, Sujit Roy Moulik, Md. S. Akhtar, A. Siawal, and H. J. Singh
ONGC, KDMIPE, Dehradun, India

The Assam shelf forms a part of Assam and Assam - Arakan basin is an established petroleum province and is situated in the northeastern part of the India. It consists of sedimentary rocks ranging in age from Mesozoic to Recent, distributed over 57000 sq. km area. The southeast-dipping broad Assam shelf is over thrusted by the Himalaya Mountain range to the north and Naga Hills on the southeast. The Assam shelf lies between these two orogenic belts and extends south-westwards across Dhansiri valley up to North Cachar hills.

Jorhat fault divides, Assam Shelf in two parts: North Assam Shelf (Upper Assam) and South Assam Shelf (Dhansiri valley). Hydrocarbon distribution in both sides of Jorhat fault is different. In North Assam Shelf, Tipam sandstone of Miocene age is directly resting over Barail coal shale of Oligocene age, where Barail main sand, sand within Barail coal shale and Tipam are major hydrocarbon producer. Where as in South Assam Shelf, the sands within Barail Formation and Tipam Formation are devoid of hydrocarbon. However, the lenticular sand within Bokabil Formation sandwiched between Barail Formation and Tipam Formation is hydrocarbon bearing.

Hydrocarbon distribution within Paleogene section is different at different stratigraphic level and tectonic block. In Borholla -Changpang area, hydrocarbon has been established in Paleocene-Eocene and fractured Basement rock in a horst and graben setup where hydrocarbon is in the horsts. Towards west and south west of Borholla -Changpang the majority of discovered hydrocarbon are at younger stratigraphic level and associated with the tectonic and sedimentation pattern of the area. The effectiveness of exploration in the area depends on the understanding of the tectonic and sedimentation pattern of the area to chase the additional newer hydrocarbon locals.

Presentation GEO India Expo XXI, Noida, New Delhi, India 2008©AAPG Search and Discovery