Peculiarities of petroleum formation in highly bituminous, siliceous, shaley, carbonaceous facies, Timan-Pechora basin, USSR
Over 50 oil and gas fields with total reserves of about 6 x 10/sup 9/ BOE have been discovered in the Timan-Pechora basin, one of the most important Russian frontiers. Almost all the sequence is productive, although major reserves are confined to two stratigraphic intervals beneath regional seals. Principal source rocks are the so-called Domanik facies represented by rapidly alternating black shales, chert, marls, and siliceous and organic limestones. Exclusively sapropelic organic matter averages 5 to 7% and reaches 20% or more. Soluble bitumen is very abundant (1 to 2 wt%) and contains all the components characteristic of crudes: from light oils to heavy tars and typical high-molecular asphaltenes. These characteristics exist even on the basin's periphery where Domanik facies are only marginally mature. The unusual composition of Domanik facies and their exceptional enrichment by sapropelic organic matter result in their peculiarities as petroleum source rocks. Lithology of the rocks, particularly the abundance of huge carbonate concretions fully or partly replaced by silica, suggests a long delay in lithification and the relative importance of the late diagenetic stage of oil generation. This explains the presence of immature oils in underlying Devonian clastics and their absence elsewhere in the sequence. On the other hand, Domanik facies, owing to significant silicification that trapped giant amounts of bitumen in the rocks, became a natural repository of oil during geologic history. This oil migrated because of fracturing, especially during stages of tectonic activity. Spatial distribution of oil types and deposits of solid bitumen in traps having different ages of formation, clearly shows predominance of pulse-like vertical migration.
- Research Organization:
- Argonne National Lab., IL
- OSTI ID:
- 6045245
- Journal Information:
- Am. Assoc. Pet. Geol., Bull.; (United States), Vol. 67:3
- Country of Publication:
- United States
- Language:
- English
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