About the deep source of the hydrocarbon’s reduced systems and origin of the Romashkin oil field

Category Other
Group GSI.IR
Location International Geological Congress,oslo 2008
Author Gottikh, Rimma۱; Pisotskiy , Bogdan۲; Plotnikova, Irina۳
Holding Date 24 September 2008

The study of deep origin of huge Romashkin oil field is based on research of microelement composition of oil and on deep structure of the crystalline basement and of the earth’s crust. The study is focused on the basement and sedimentary rocks penetrated by wells on the Romashkino oil field (South Tatarstan Arch of the East European Platform) and on the oil from Romashkino and another oil fields of Volgo-Ural region. The acquired geochemical and thermodynamic characteristics of the reduced fluids and their differentiation products from the crystalline basement and the sedimentary cover indicate that these were formed outside of the sedimentary cover and that the migration was directed upwards.
The first results of the analysis of have shown that levels of many chalcophilic trace elements in oil considerably exceed their levels in sedimentary rocks and in the upper part of the Earth’s crust. The oils of Tatarstan are characterized by the presence of palladium and iridium. The distribution of elements of the platinum group is similar to the ratio of these elements in the basic-ultrabasic intrusion. The level of elements of the platinum group in oil considerably exceeds their contents in sedimentary rocks and in the upper part of the Earth’s crust. The distribution of chalcophilic trace elements is similar to the ratio of these elements in the volcanic gases. Studying of isotope structure of oil has shown that oil from various horizons and areas is characterized by different evolution of isotope composition. It has been found that asphaltenes have a distinct, positive europium-produced anomaly and a ratio of Eu/Sm reaching 1.16 that is obviously not characteristic of the upper crust formations. Thus, the source of these microelements can only be found in the lower crust or upper mantle. Strontium isotopic ratios provide another piece of evidence that oil has no relation to the «producing» sedimentary material. Devonian aphanite limestone from the sea area is characterized by the 87Sr/86Sr ratio of 0.7082, and oil from the Nurlat and Abdrakhmanovo areas - by 0.7102 and 0.7100, respectively. However, the biogenic concepts suppose that the oil should have inherited some sea-related matter.
Strontium isotopic systems and neodymium in petroleum and carbonic rocks were evolved in different ways. Strontium isotopic ratios provide that oil has no relation to the producing sedimentary organic material of Domanic horizon. Diagrams of eNd–87Sr/86Sr, have shown that microelements found in petroleum might have their sources in magmas of varying composition, in active zones of the lower-crust substratum and in the mantle. Geophysical data have also confirmed that gas systems reached the upper mantle and earth’s crust to undergo polymerization and polycondensation.