Commercial oil and gas are found in a wide stratigraphic range on the Russian platform; however, no commercial discoveriers have been made in a thick sedimentary section between the Devonian and basement. The oldest sedimentary rocks of the Russian platform are Riphean in age, deposited about one billion years ago. They are preserved in several aulacogens. The overlying Vendian sedimentary rocks are more widespread. These have been best studied in the Moscow sineklize, a structural feature that extends in a northwest direction through the central part of the Russian platform for a distance of 1200 km. Its width ranges from 600 km in the middle part to 300 km on the ends. The Moscow sineklize joins on the north the Mezen sineklize through the Sukhon downwarp.
Two groups of Precambrian oils have been found in non-commercial pools of the central part of the Russian platform. The first group includes light oils. Prominant in their composition are low-molecular n-alkanes, isoalkanes including isoprenes, and small amounts of arenes and other high-molecular compounds. These oils are classified as "young". The second group of oils are found in the east of the Russian platform. These oils are lean in low-molecular components and enriched in high-molecular types. As a consequence of being "older", these oils contain much less dissolved gas and light fractions.
Conditions were very favorable for accumulation of organic matter in the Proterozoic rocks. It was supplied by bacteria and algae. In Late Proterozoic time there was a veritable explosion in the evolution of living forms. In the Moscow sineklize the rocks of the Redkin Formation have all the characteristics of source beds. Black argillites, called the "Vendian Domanik", have a particularly high content of organic matter. Bituminous layers can be ignited, and they burn hot.
Sandstones are widespread at the base of several sedimentary cycles of the Precambrian of the Russian platform. Porosities as high as 30 percent have been recorded.
Cyclical sedimentation, particularly in the Vendian-Cambrian stage, resulted in alternation of sandstone and clay members in the section. The clay members form seals for underlying sandstone reservoirs. One of the regional seals are argillites of the Redkin Formation, thickness of which is uniform in the 50-150 m range.
Owing to the low extent of study of these ancient rocks, not a single local trap has been delineated. General characteristics of these rocks, however, suggest that a large number of traps of various kind are present. The Yurubchen-Tokhom oil-gas zone of the Riphean and Vendian of the Siberian craton may be an analog of graben-horst traps in several aulacogens of the Russian platform.
Only a few well have been drilled in the Mezen sineklize, and only about 10 percent of the Moscow sineklize has been covered by common depth point seismic surveys. Nevertheless, it has been established that all the prerequisite conditions are present for oil and gas deposits in the Riphean-Vendian rocks of the Russian platform.
Taken from Fedorov, 1994; digested in Petroleum Geology, vol. 29,
no. 1/2, one map and one cross section.
Copyright 2001 James Clarke. You are encouraged to print out this
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