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Application of High Resolution Sequence Stratigraphy for Petroleum Exploration of Mixed Siliciclastic - Carbonate Associations in Middle Eocene Sylhet Formation, Dhansiri Valley, Assam Arakan Basin, Northeast India

Anupma Baveja, A. S. Kale, U. S. Kanungo, and Md. S. Akhtar
Basin study, KDMIPE,ONGC, Dehradun, India

A number of oil and gas fields have been discovered in the Middle Eocene Sylhet Formation in the Dhansiri valley of Assam Arakan Basin located in north eastern India. The reservoir potential of Sylhet Formation in the basin lies in the prediction of development of siliciclastic facies within the carbonates. This was accomplished by establishing a sequence stratigraphic framework for the Eocene succession in the Dhansiri valley by detailed petrophysical interpretation, facies analysis and seismic calibration. It has enabled in identification of high frequency cycles and their progression across shelf with predictive facies movement as brought out by each depositional model.

The study has interpreted the entire Eocene Sylhet succession along the length of the Shelf margin as comprising of six transgressive/regressive episodes (SU-IA, IB to V). Facies analysis has led to the reconstruction of paleodepositional environments, a critical pre-requisite for a successful sequence stratigraphic interpretation. It is observed that the spurs or tectonic elements of Mikir Hills may have influenced the facies distribution in the area which is duly supported by various geological maps. Facies analysis has revealed the presence of distinctive sand lobes shifting with reference to the transgressive and regressive cycles. Mixed siliciclastic and carbonate facies is observed within transgressive phases SU-IB, II, III and regressive phase SU-IV of the T-R cycle while transgressive parasequences SU-IA and V are dominantly limestone facies. The findings indicate that the principal oil exploration target in the Dhansiri valley should be the sandstone/siltstone reserviors corresponding to the major regressive pulse SU-IV and the initial transgressive backstepping phases SU-IB, II and III of the Transgressive cycle.

Presentation GEO India Expo XXI, Noida, New Delhi, India 2008©AAPG Search and Discovery