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Global discovered resources of oil and gas in giant stratigraphic and structural-stratigraphic combination traps have increased by nearly 50% in the last 17 years. Among the biggest contributors are the large discoveries in deepwater turbidite systems in passive margins and rift basins. The current study area is located in the Barmer Basin in northwestern India. Barmer Basin is a prolific petroliferous basin with major oil discoveries in structural plays including Mangala, Bhagyam, and Aishwariya fields. The principal reservoirs in the structural highs are high-quality fluvial sandstones of the Paleocene Fatehgarh Formation. Lacustrine turbidite plays have been discovered in the overlying Paleocene Barmer Hill Formation, albeit with moderate to poor reservoir quality. The potential exists, however, for finding off-structure lacustrine deepwater turbidite plays in the Paleocene Fatehgarh with reservoir quality comparable to the high-quality fluvial facies encountered updip in the structural plays. An integrated approach was adopted to identify stratigraphic entrapments across the basin to chase high-quality Fatehgarh reservoirs. Gross depositional environment maps integrating new geoscientific data were created, followed by well-calibrated seismic geomorphology and seismic facies interpretations to identify the distal lacustrine deepwater turbidite system fed by the updip fluvial Fatehgarh systems. Worldwide, the critical risk elements associated with such plays are reservoir presence, quality, and lateral seal. Geophysical tools like unsupervised seismic waveform classification, spectral decomposition, and seismic inversion were applied to the available seismic data, and the results were integrated with the regional geology and well facies information to derisk the critical risk segments.

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The study area, block SL-2007-01-001, operated by Cairn India Ltd., is located in the Mannar basin of NW offshore Sri Lankan (blue polygone in Figure-1) and contains a sedimentary section exceeding 7km, the age of which ranges from Jurassic to Recent. The large number of oil and gas discoveries in the contiguous Cauvery Basin, both in Cretaceous and Tertiary sections, makes this frontier basin an attractive candidate for exploration. In 2010 Cairn Lanka acquired 1753 sq km of 3D seismic data in order to assess the exploration potential of this deep water block. This paper focuses on the role that rock physics analysis played in the assessment, risking, and ranking of the key leads identified in the basin. Of the numerous leads identified, three were high-graded in large part due to their DHI characteristics, resulting in the Dorado and Barracuda gas discoveries (Well-A & Well-C in Figure-1, respectively), the first hydrocarbons to be discovered in the Mannar Basin. The third well, Well-B, was a dry hole. De-risking of exploration prospects was based on quantitative seismic interpretation supported by rock physics analysis. This paper emphasizes how rock physics can add value in an exploration project to influence business decisions by reducing subsurface uncertainties. The nearest well, CY-DWN-2, that provided data for depth trends and rock physics analysis is located approximately fifty kilometers south west of the study area. Although this was a dry hole, it provided significant information on the sedimentary sequence, rock properties, and their associated seismic responses. Various "what if" scenarios were created to understand associated seismic responses. The analsyis explained the dry hole at CY-DWN-2 and highgraded the prospectivity of the Dorado lead. The latter was subsequently drilled, leading to the Dorado discovery.

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