Abstract: Geochemical Characteristics of Overmature Petroleums from Different basins of the Former Soviet Union: Prediction of Oil Discoveries at Great Depth

CHAKHMAKHCHEV ALEXANDER

In the present paper, overmature petroleums from different basins of the Former USSR including the Western Siberia, Forcaucasia, Buzuluk, and Precaspian have been characterized geochemicaly in order to reveal major changes in their composition over a wide range of maturity. The oil and condensate samples selected for this study have variable ages and derived from the source rocks characterized by different lithologies (carbonate, mixed, argillaceous) and organic facies. These petroleums have been produced from the sedimentary deposits located below the `oil window" in overmature zone where high values of vitrinite reflectance in the range of Ro=1.1-1.3% have been measured. Geochemical characterization of overmature petroleums were performed in comparison with low/moderately matured oils and based on dramatic changes in the composition of gasoline-range hydrocarbons, alkanes, biomarkers and polycyclic aromatic compounds. Behavior of maturity indicators in oils derived from different sources has been observed and best indicators for each geological situation have been proposed. Stability of oils to thermal stress and the factors which may suppress oil cracking to gas at high temperatures in certain geological settings are discussed in this study. Results obtained can be used for exploration in the deeper parts of the petroleum basins where commercial accumulations of liquid hydrocarbons can be discovered.

AAPG Search and Discovery Article #90942©1997 AAPG International Conference and Exhibition, Vienna, Austria