Hydrocarbon potential in Indian deep waters

Abstract

Deep-water exploration is a natural step forward to assess and accrete hydrocarbon reserves after having accomplished this task to a certain extent along the continental shelf areas of India. In recent years Oil and Natural Gas Corporation Limited of India (ONGC) has made a gradual but steady progress in the deep-waters beyond the 200 m isobath exploring for hydrocarbons, acquiring multichannel seismic data and other geoscientific data. Hydrocarbon potential in the deep-water areas of five offshore basins viz. Kutch, Bombay, Kerala-Konkan, Cauvery and Krishna-Godavari is analysed in this paper. The evolution of these polycyclic basins was initiated as intracratonic rifts in divergent margins set up at different geological times. Later these basins acquired a pericratonic character evolving through typical syn-rift and post-rift phases. The recently acquired seismic data corroborate the extension of identified lineaments of onshore and shelf into deep-water areas, differentiating the deep-sea basinal region into segmented linear ridge-depression complexes. The sedimentary thickness in these deep-sea basins varies from 2 to 8 km, with thicker areas being near the shelf break and in areas over 2500 m water depth near the various river mouths in the basins. The hydrocarbon potential of deep-waters of India covering about 1.4 million km2 of the Indian offshore is estimated to be between 5.0-9.0 billion tons of oil and oil equivalent gas. Analysis of about 90,000 line km seismic data has helped in identifying and mapping the geological features such as submarine fans, turbidites, build-ups, wedge-outs, growth fault-related rollover anticlines and other structural features relevant to hydrocarbon prospectivity in these basins. These prospects range in area from 10 to 600 km2, in water depths from 300 to 2000 m. The average prospect size is about 200 km2 in the western offshore and about 20 km2 in the eastern offshore. Exploration of these will help in establishing a reserve base for India's future energy supply.