Lithofacies and Petroleum Prospect Analysis of the Oligocene Barail Group, the Bengal Basin and Shillong, Northeastern India.

Abstract

The Oligocene deposits of the Bengal Basin, known as the Barail Group, exposed along the northern fringe of the Sylhet trough in the foothills of the Shillong Plateau and near the Dauki fault zone, varies in thickness from 800 to 1600 meters. The Barail Group equivalent (Bogra Formation) has been drilled in the northwestern part of Bengal Basin. These Oligocene formation consist of thick sequence of medium to coarse-grained sandstone, intercalated with siltstone, mudstone, and conglomerate deposited at a prograding Himalayan foreland basin. The depositional environments of this group range from tide-dominated shelf environment for the Barail Group to estuarine, deltaic to high energy coastal conditions for the equivalent Bogra Formation. In an effort to reconstruct the depositional environment and to determine the petroleum prospect, the focus of this study is to analyze the outcrop samples from northeastern part of the Sylhet trough and drilled-core samples from northern Bengal Basin and compare it with the equivalent rock unit, exposed in southern part of the Shillong, India. Petrographic and microprobe analysis of sandstone and mud-rock units will be used to develop lithofacies models in order to determine the depositional environment. This study will also include data on vitrinite reflectance, rock-eval pyrolysis and Total Organic Carbon (TOC) to identify the source rock potential of the Barail Group. Petrographic and geochemical study of the coarser sand fractions will be evaluated for their potential as a petroleum reservoir rock.

AAPG Datapages/Search and Discovery Article #90351 © 2019 AAPG Foundation 2019 Grants-in-Aid Projects