Geochemical Characterisation and Source Investigation of Oils from Narmada Block of Cambay Basin, India

Bhatnagar, A.K.¹, B.G. Goswami², D.S. Rawat³ (1) OIL &NATURAL GAS CORPORATION LTD, Dehradun, India (2) KDM Institute of Petroleum Exploration, ONGC, Dehradun, India (3) ONGC, Dehradun, India

The depocentres in Narmada block of South Cambay basin are relatively small and good source rocks with adequate maturity did not develop. Hence a need was felt to trace the origin of Narmada block oils. In order to understand their generation and migration path, source sequences from North of Narmada block i.e. from Broach block of Cambay basin and also from west i.e. from Navasari Low of Tapti-Daman sub-basin of Mumbai Offshore Basin were studied for their geochemical and biomarker parameters. The source rocks data was compared with the characteristics of oils from Narmada block to establish oil-source correlation. The source sequences within Cambay Shale (Eocene) and Olpad (Paleocene) formations in Broach block were deposited in sub-oxic marginal marine environment having mixed organic matter input and are mature enough to generate and expel liquid hydrocarbons. These sediments in Narmada block, were deposited in sub-oxic environment having more terrestrial input and are in early catagenetic stage. In Navasari Low depression, the source sequences were deposited in fluctuating marine environment with mixed source input and are sufficiently mature. Narmada block oils have been generated by mixed source facies deposited in sub-oxic marginal marine environment at moderate maturity. Narmada block oils correlate with source sequences within Cambay Shale Formation of Broach block. These oils do not match with source rocks from Narmada block as well as source sequences within Panna Formation from Navsari Low depression of Tapti-Daman sub-basin. The geochemical studies suggest that the Narmada block oils were generated in the North in depressions of Broach block and were migrated to the South probably along the faults in the reservoirs of Narmada block.