ISOTOPIC COMPOSITION AND NATURE OF GASES IN THE NORTH OF WESTERN SIBERIA

Summary Were determined the carbon isotopic composition (δ13C) of methane and its homologues (C2-C5) for more than 150 gas samples from 26 different fields in the North of Western Siberia (Gydanskaya and Nadym-Pur-Tazovskaya oil and gas bearing areas). Several genetic types of gases were identified based on the obtained results. First group - gases directly from the Bazhenov Formation (Upper Jurassic source rock which content marine type of organic matter) have a sublinear view and C1-C5 components have the same origin. Second group - gases that were generated by source rocks, where the organic matter had been formed mainly in the lake-marsh facies of the Lower and Middle Jurassic. Third group - microbial gases and gases genetically related to the nonmarine organic matter of the Jurassic, another group of gases is found in the Upper Cretaceous rocks (Turonian, Cenomanian). A distinctive feature of these gases is the abnormally light isotopic composition of ethane (-54...-51‰) and propane (-45...-43‰). Fourth group - biodegraded gases. A distinctive feature of these gases is heavy isotopic composition of propane and butane carbon.