ABSTRACT: Multiple petroleum systems in parts of upper Assam Basin, India

Srivastava, S. K., N. M. Borah, and V. Ravichandran, Oil India Limited, Duliajan, Assam, India

The Upper Assam Basin is a major sedimentary basin situated in Assam-Arakan province in the northeastern part of India. The present day basin represents a structurally warped foreland basin with a platform ramp and foredeep between two convergent margins. The area is covered, over large part, by shelf sediments that grades into geo-synclinal facies. The basin is characterised by a central northeast - southwest trending buried "basement ridge" which is continuation of exposed Pre-Cambrian basement in the west. The basin contains Tertiary sediments ranging from 3.6 kms. to over 7 kms., which include shallow marine and deltaic Paleogene clastics with minor carbonates and continental fluviatile Neogene clastics. Syn and post-depositional folding and faulting is observed in the platform and foredeep parts of the basin.

The platform complex, which is the extension of ancient passive margin, contains a number of oilfields within different stratigraphic intervals. The occurrence of hydrocarbon accumulation in varied plays follows distinctive patterns. Three prominent petroleum systems exist in the southern part of the basin, which are i) Lakadong+Therria System of Lower Eocene-Paleocene age lying close to the basement ridge, ii) Barail System of Lower Oligocene age on the ramp and iii) Tipam-Girujan System of Miocene age in the deeper part of the platform ramp and in the foredeep close to the thrusts and associated accretionary wedges. This system also continues in the Belt of Schuppen in the supra thrust anticlines. The petroleum systems in the Upper Assam basin are controlled by varied tectonic elements.

AAPG Search and Discovery Article #90913©2000 AAPG International Conference and Exhibition, Bali, Indonesia