Sedimentological Insights into Upper Cretaceous Deepwater Sediments from Ramnad Area of the Cauvery Basin, India

Dilip K. Bharktya, Pradeep Goswami, M. Nagaraj, and B. Bhaskaran
Regional Lab, Oil and Natural Gas Corporation, Chennai, India

The Ramnad sub basin is the southern part of Cauvery Basin with hydrocarbon fields in Periyapattinam, Perungulam, Ramanavalasai, and Kanjirangudi areas. The main pay sands are from Bhuvanagiri and Nannilam formations comprises mass gravity sandstones of Turonian to Santonian age and deposited during post rift phase in deepwater setting.

Sedimentological studies of available cores across the area revealed that reservoir sands of Bhuvanagiri formation are represented by massive sandstone with presence of floating clay clasts and granules and deposited by debris flow process. Dish structures formed by escaping pore fluids are also present within this unit. Sediments in Nannilam Formation are also deposited by dominantly gravity flows with intermittent traction currents. Massive sandstone with floating clay clasts and claystone with clay clasts suggest that they have been deposited by sandy and muddy debris flow process. Besides, presences of horizontal and discontinuous laminations/beddings which are bioturbated indicate bottom current activities and separate the debris flow intervals. The source and transport of these sands may be from NW direction. In NW area at Koluvur, sandy debris flow dominates whereas sediments at Ramanavalasai and Perungulam are deposited by mixed processes of sandy and muddy debris flow.

Reservoir facies in Bhuvanagiri Formation is arkose sandstone showing moderate compaction, early calcite cementation, quartz overgrowth and filling of pores by chlorite leading to loss of primary porosity. Reservoir sands of Nannilam Formation are similar to Bhuvanagiri sediment with the presence of glauconite mineral as detrital composition. Secondary porosity is generated due to dissolution of feldspar and calcite cement and has an improving trend from SE to NW region. Reservoir characteristics are better in sands of Nannilam Formation.

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