Geologic Setting and Petroleum System of Heavy Oil Occurrences in Sedimentary Basins of India

摘要

Heavy oil, in commercial quantity, has been on production from a linear tectonic belt in the central Cambay Cenozoic rift basin of western India. Recently heavy and nonbiodegraded oil has been discovered from the late Riphean-Vendian strata in Bikaner-Nagaur peripheral foreland basin situated to the north west of Indian shield. Heavy oil belt of Mehsana sub-basin of Cambay rift lies close proximity to the intrabasinal axial high (Mehsana horst) which has undergone synchronous episodic upliftment since early-middle Eocene i.e., deposition of Cambay shale source facies. Occurrence of heavy oil is confined to the pinch-outs of the post rift clastic sequence along the eastern peripheral part of the axial high and in an inversion structure, south-west of Mehsana horst. Generation and migration of oil of Cambay-Kalol (!) petroleum system ranges from Miocene onward. Depletion of nalkanes of the high asphaltic oil, in contrast to the oil of the surrounding fields, is probably due to mild bioldegradation. The stable carbon isotopic study infers that oil is generated from the source rock of low maturity at an early stage of catagenesis.