ABSTRACT: Prediction of Oil and Gas Potential in Petroleum Complex for Arctic Regions of Northern West Siberia

NEMCHENKO, N., Deputy Chairman of State Commission for Mineral Reserves of the USSR, Moscow, Soviet Union, and A. S. ROVENSKAYA, Senior Scientist of the IGIRGI, Moscow, Soviet Union

In northern West Siberia, a zone of petroleum accumulation has been identified. A characteristic feature of this zone is the development of a thick (up to 2000 m) Cretaceous (Neocomian-Cenomanian) complex, with which the bulk of the gas and gas-condensate resources of West Siberia is associated. The Cretaceous complex comprising the coal-bearing association is marked by a high gas generating potential. The formation of gas-condensate deposits has clearly been associated primarily with the gas systems. A study of the individual composition of the hydrocarbons in the benzene fraction of the condensates of northern West Siberia has shown that the condensates of the Cretaceous complex are marked mainly by anaphthene composition. In the model for vertical zonation of hydrocarbons in northe n West Siberia, a low-temperature zone of generation of naphthenic primary condensates is distinguished, connected genetically with the coal-bearing association -- "primary" naphthene gas-condensates have developed, formed during the brown coal phase of catagenesis of humic organic matter and associated with a major zone of gas accumulation, confined to the region of development of the coal-bearing association. The formation of the upper low temperature zone of generation of "primary" condensates in northern West Siberia is no exception. Such zones could also have been formed on other young platforms. On older platform, the upper gas-condensate zone is generally not recognized, which is evidently connected with the absence of conditions for its formation and especially for its preservati n.

The confinement of the gas accumulations to coal-bearing sediments, the compositional features of the natural gases, which are virtually devoid of heavy hydrocarbons, the similar absolute values of the carbon-isotope composition of the methane in the gas deposits and marsh gases, the scale of generation, and the nature of their distribution, have led to the conclusion that the principal source of gas in the Cenomanian sediments was organic matter of humic type, the carbonized remains of which saturate the entire rock sequence of the Ust-Tazovskly supergroup. The gas deposits are not genetically associated with the underlying oil envelopes, although such a combination (dry gases and heavy naphthene oils devoid of benzol fractions) is well known and although such gas caps are usually of insignificant size. The much larger Cenomanian gas deposits could not have been formed from light oil fractions. The processes of gas and oil accumulation in the sediments of the complex took place independently.

The investigation carried out suggests that the northern regions of West Siberia are promising in the search for deposits of liquid hydrocarbons,

and the most promising area for liquid hydrocarbons is the main zone of oil generation within the northern part of the West Siberian province.

AAPG Search and Discovery Article #91015©1992 AAPG International Conference, Sydney, N.S.W., Australia, August 2-5, 1992 (2009)