ABSTRACT: Molecular geochemistry as indicator of petroleum systems in Cambay Basin, Western India

Oil-oil and oil-source correlations based on molecular geochemistry of crude oils and source rocks in Cambay Basin have indicated the existence of two mega petroleum systems (source-reservoir systems), one in the North Cambay and the other in the South Cambay and some other petroleum systems. Crude oil occurrences are known ranging from Paleocene through Miocene but most of the occurrences are located in Middle Eocene. Cambay Shale of Lower Eocene age is known to be the major source rock in the entire basin.

The molecular geochemical parameters (like low pristane/phytane ratios, presence of C30 steranes in varying amounts, high hopane/sterane ratios, presence of petroporphyruns etc.) of source rock bitumens and crude oils form North Cambay indicate a lacustrine organofacies. A deltaic organofacies is indicated for South Cambay from parameters like high pristane / phytane ratios, presence of angiospermic plant derived biomarkers etc. Maturation levels are higher in South Cambay. While a large number of Middle Eocene oils in the North Cambay exhibit above characteristics and are sourced by Cambay Shale, some oils indicate a different source , possibly Olpad (Paleocene)/lower part of lower Cambay Shale. Similarly, while most of the Middle Eocene oils of South Cambay exhibit above characteristics and are sourced by Lower/Middle Cambay Shale, a few oils indicate a different source, possibly Upper Cambay Shale. These inferences are in consonance with the geological considerations like structural elements, tectonics, charge factors, migration drainage style and entrapment style.

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