Sedimentation, stratigraphy, and petroleum potential of Krishna-Godavari basin, East Coast of India

Abstract

The Krishna-Godavari basin is located in the central part of the eastern passive continental margin of India. The structural grain of the basin is northeast-southwest. Exposures of Upper Cretaceous sedimentary rocks demarcate the basin margin toward the north west, where the northwest-southeast-trending Pranahita-Godavari graben abuts the basin. The basin contains thick sequences of sediments with several cycles of deposition ranging in age from Late Carboniferous to Holocene. A major delta with a thick, argillaceous facies that has prograded seaward since the Late Cretaceous is a hydrocarbon exploration target. Magnetic and gravity data predicted the basin architecture, which was subsequently confirmed by a multichannel seismic sur vey. The basin is divided into subbasins by fault-controlled ridges. Sediments accumulated in subbasins more than 5 km thick. Above the basement ridges, thin sediments are found. Until the Jurassic period, sediments were deposited in the rift valley and in topo graphic lows. This sequence is completely overlain by a Lower Cretaceous, transgressive sedimentary wedge. Later, continued delta progradation characterized basin sedimentation. With an areal extent of approximately 45,000 km2, this proven petroliferous basin has potential reservoirs ranging in age from the Permian to the Pliocene. Exploratory drilling of more than 350 wells in more than 160 structures has resulted in the discovery of 42 oil and gas bearing structures. Good source rocks are known from sequences ranging in age from Permian-Carboniferous to early Miocene. Because the reservoir sand bodies have limited lateral variation, understanding the stratigraphy and depositional sub environments in different sequences is essential to decipher the favorable locales for reservoir sands. Tilted fault blocks, growth faults, and related rollover anticlines provide the structural traps. (Begin page 1624)