Source rock potential in sediments of Shelf Margin area of Bombay Offshore, analogous to surficial sediments of Arabian Sea, West Coast of India

摘要

Organic type in Oligo-Miocene sediments in drilled wells is found to be more of humic nature in Saurashtra and sapropelic in Shelf Margin wells with high organic carbon content (1.5 to 2.6 %). Studies on the present day seabed sediments of Bombay Offshore indicate that biogenic activity is very high at the shelf edge on the slope part due to the process of upwelling along the slope. This organic matter is well preserved in the sediments due to presence of thick oxygen minimum zone between 100 to 1500m water depth in the northern part of Arabian Sea. The geologic set up of the Shelf Margin Basin indicates that from Late Oligocene onwards the shelf edge has prograded for more than 50 km from the edge of Bombay platform from east to west, covering Shelf Margin and Saurashtra depressions. The present day sea bed data are analogous to conclude that Miocene sediments with high percentage of TOC in the wells of the study area were deposited in paleoslope setting. Well data indicate that top of oil window in this area is at around 2900m depth. The Paleogene sediments generally fall within oil window whereas most of the lower part of Neogene sediment with higher TOC percentage falls under gas generation window. Focussed exploration may lead to commercial accumulation of hydrocarbons in this part of the Bombay sub-basin, as well as in the deep waters towards its west.