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.