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Prospectivity of Cauvery Basin in Deep Synrift Sequences, SE India

Chaudhuri, Arijit 1; Rao, M. V.1; Dobriyal, J. P.1; Ramana, Lalam V.1; Murthy, K. S.2; Saha, G. C.1; Chidambaram, L. 1; Mehta, A. K.1
1 Geology, ONGC Ltd., Chennai, India.
2 Sclumberger Inc., Kuala Lumpur, Malaysia.

Cauvery basin, situated on the south-eastern tip of India, comprises six sub basins separated by intervening basement ridges. All the sub basins excepting the Gulf of Mannar have proven oil and gas pools from clastic reservoirs with age ranging from Aptian-Albian to Oligocene and also from Precambrian basement. The proven source is Type III kerogen with subordinate Type II of early Cretaceous age.

The basin originated with Gondwanaland fragmentation in the Late Jurassic. Based on the seismic data, the basin appears to have opened from the south where the pre/syn rift strata are much thicker.

A distinct relation between deep basement penetrating faults and hydrocarbon migration is observed in most accumulations. The faults are established as proven conduits for the established pays.

The already established hydrocarbon bearing reservoirs of Tertiary and Cretaceous age have remained the target of intensive exploration by the current operators. The anticipated syn-rift fan deltas and the reservoirs resulting from axial drainage as well as hanging wall transverse drainage remained, by and large, unexplored. So far, seismic API concentrated typically on the shallow targets between 1500 to 2500m excepting in the Ariyalur sub basin of North Cauvery.

Critical moment of the late syn rift (Aptian-Albian) source facies drilled in Cauvery basin ranges from Late Cretaceous to Tertiary age (50%. transformation of kerogen). Modelling of source facies predicted in the older undrilled sequences indicates early maturation with critical moments within Lower Cretaceous. Similar to other rift basins all over the world, Cauvery Basin is very likely to have source rich lacustrine facies at the early syn-rift stage. Early maturation of such source would have resulted in hydrocarbon accumulation in hitherto unexplored deeper stratigraphic levels. The southern sub basins of Ramnad, Tanjore and Nagapattinam may turn out to be big producers with the shift of focus to the deep reservoirs.


AAPG Search and Discovery Article #90090©2009 AAPG Annual Convention and Exhibition, Denver, Colorado, June 7-10, 2009