The Geology and Petroleum Systems of the Mannar Basin, Sri Lanka

Mohapatra, Pinakadhar; Srinivas, Mokashi; Kumar, Neeraj; Routray, Prabir; Adhikari, Subhrashis; Daly, Cathal
Exploration, Cairn Lanka (Pvt) Ltd, Gurgaon, India.

The Mannar Basin is located off the western coast of Sri Lanka and contains a sedimentary section exceeding 7km in thickness, the age of which ranges from Jurassic to Recent. The basin developed during the rifting and related continental break-up associated with the fragmentation of Gondwanaland during Late Jurassic. Flanked by the Pre-Cambrian massif of Sri Lanka in the east and the craton of the south Indian massif to the west, the basin contains a complex sequence of potential source and reservoir rocks. An extensive early Cretaceous source kitchen has been mapped over large parts of the basin. Basin modeling suggests that the source rock in this kitchen entered the oil window some 40 Ma and the gas window about 20 Ma.

Potential deep water reservoirs are represented by channel-levee complexes, slope fans and basin floor fans observed in the Cretaceous and Tertiary sequences. Thick sand packages are observed in the Late Cretaceous and Tertiary in the recently drilled wells in the basin, with log-based porosities of up to 30%.

The presence of multiple play types, including four way structural closures, stratigraphic pinch-outs, rotated fault traps and deep water channel-fan systems provide positive impetus to the hydrocarbon prospectivity in this frontier territory.

Cairn Lanka recently completed a three well drilling campaign in Sri Lanka Block SL 2007-01-001. This programme resulted in two successive gas and condensate discoveries in sandstone reservoirs of Cretaceous age. The drilling programme, the first in Sri Lanka in 30 years, has established a working petroleum system in the frontier Mannar Basin.

AAPG Search and Discovery Article #90155©2012 AAPG International Conference & Exhibition, Singapore, 16-19 September 2012