Phanerozoic Petroliferous Basins of India
Keshav Deo Malviya Institute for Petroleum Exploration, Oil and Natural Gas Commission, 9, Kaulagarh Road, Dehradun - 248 195 The term Phanerozoic or “revealed life”, which is applied to Paleozoic, Mesozoic and Cenozoic eras, represents a relatively brief geological period of half-a-billion years that constitutes the age of multi-cellular animal life on Earth, and which left a detailed fossil record and built up complex and diverse ecosystems. Though there was complex Late Precambrian (Vendian/Ediacaran) biota, the Phanerozoic period defines the period of development and evolution of higher groups of organisms like arthropods, mollusks, vertebrates, etc. The sedimentary basins of India have received attention of geoscientists due to increased activities for petroleum exploration since 1950’s. Sophisticated geophysical technique together with drilling made it possible to obtain vast amount of subsurface data, and tied wherever possible with surface geology. These gave new insight into the mechanisms of various types of basin formation and their relationship with the different petroleum occurrences. In India, hydrocarbons have been struck in different basins ranging in age throughout the Phanerozoic. The most relevant feature has been the occurrence of most of the commercial hydrocarbons within the Cenozoic successions both on land and offshore. The Mesozoic, comprising a shallow marine Jurassic succession in Kutch-Rajasthan and poorly developed shallow shelf facies of the Cretaceous in most parts of the eastern coastal basins between Assam and southern tip of India, have had relatively lesser hydrocarbon finds till date. We have, however, the Gondwana successions in several parts of the country which contains rich coal deposits where exploration for coal bed methane (CBM) has taken off in a big way. Not all the Phanerozoic sedimentary basins in India are equally prospective, as borne out by the oil exploration programme and a small number of basins produce most of the hydrocarbons. Proven petroliferous sedimentary basins with commercial production include the Mumbai offshore, Cambay, Assam-Arakan, Cauvery, KrishnaGodavari and Tripura-Cachar basins. Sedimentary basins with known occurrence of hydrocarbons but lacking commercial production include Andaman-Nicobar, Bengal, Mahanadi, Himalayan Foothills and Rajasthan basins. Basins which on general geological grounds appear fairly prospective but where significant amounts of hydrocarbon have not yet been found, the Kutch-Saurashtra and KeralaKonkan basins. Lastly, basins like Arunachal Foothills, Deccan syneclise, Ganga Valley, Karewa (Kashmir Valley), Mizoram-Manipur and Narmada basins, could still be considered in the initial phase of exploration. The geoscientific studies by ONGC in the petroliferous basins of India from are summarized in the present contribution, and * E-mail: firstname.lastname@example.org
takes into account, the interpretations based on real well data, the seismic and other geophysical information, multimicrofossil bio-stratigraphy, sedimentology and geochemistry. More specifically, we deal with, 1. Sedimentary petroliferous basins along the Western margins: viz. Rajasthan, Cambay, Kutch, Mumbai Offshore and Kerala- Konkan 2. East Coast Basins: Cauvery, Krishna-Godavari, Mahanadi and Bengal basins 3. Northeast Basins: Assam and Assam-Arakan basin 4. Central Indian Basins: Ganga and Purnea basins Each basin has been discussed with reference to its basin architecture, sedimentary fill, major unconformities, sequences and petroleum system, in light of latest understanding of these basins and their hydrocarbon prospectivity. SEDIMENTARY PETROLIFEROUS BASINS ALONG THE WESTERN MARGINS Two important phases of basin evolution are recorded along the western continental margin. There is an initial record of the Mesozoic basins in Jaisalmer, Bikaner-Nagaur, Barmer (Rajasthan Basins), Kutch, and Cambay that could be...
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