Abstract

Upper Assam Shelf, a southeast dipping shelf over thrust by the Naga Hills is a foreland part of Assam-Arakan Basin. The present study aims to identify the elements and processes making up the petroleum system of upper Assam shelf to assist in prioritizing future exploration effort. Source rocks mainly in Barail, Kopili and Sylhet/Tura formations of the Schuppen belt have charged reservoirs in upper Assam shelf since Late Miocene. Reactivation of structures and developing folds in the foreland possibly created impedance to lateral migration from the Schuppen Belt since Pleistocene. Migration is primarily updip to the northwest along the northeasttrending slope and occurs through reactivated basement-rooted faults. In Nazira low and adjoining area, hydrocarbon charge from local Sylhet/Tura, Kopili and Barail source rocks of the foreland has caused diversity in oil characteristics. In Dhanasiri valley, uniformity in oil characteristics is due to lack of local generation. Two oil groups are evident; one predominantly matching to source rocks of Oligocene and Late Eocene sequences, another matching to source rocks of middle Eocene to Paleocene sequences.