Tectono-stratigraphic evolution and petroleum systems of Krishna-Godavari Basin, India

摘要

Four distinct tectono-stratlgraphic cycles in the evolutionary history of the Krishna-Godavari Basin are imprinted in its stratigraphic record. These are (ⅰ) early rift, (ⅱ) rift, (ⅲ ) early thermal subsidence, and (ⅳ) late thermal subsidence. The early rift setup is the reminiscent of Gondwana rift containing Permo-Triassic sediments, laid down by continental depositional systems. The rift stage represents a later rifting episode during Late Jurassic to Early Cretaceous, leading to development of NE-SW aligned horsts and grabens filled up with fluvial and lacustrine sediments overlain by initial marine deposits. The early thermal subsidence is characterized by southeasterly tilt of the basin as the cooling edge of the continents sagged oceanwards. A regional marine transgression during Cenomanian to Campanian/Maastrichtian, followed by a regressive phase marks this stage. The late thermal subsidence witnessed accentuation of the basin slope and consequent up- and outbuilding of deltaic systems during Tertiary. Each tectono-stratigraphic unit, with its unique tectonic and sedimentary setting, is characterized by its distinct hydrocarbon habitat. Five petroleum systems namely, Kommugudem-Mandapeta, Golapalli-High gamma-high resistivity Shale, Raghavapuram, Palakollu-Pasarlapudi, and Rawa, are defined in the basin. Of these, one petroleum system each is related to the early rift, rift, and early thermal subsidence sequences, and last two to the late thermal subsidence sequence. All these petroleum systems are speculative and dominantly characterized by close association of reservoirs and hydrocarbon generating centres and short distance migration.