Some of the petroleum accumulations of the Timan-Pechora and West Siberian platforms are related to faults in the sedimentary cover. In the Timan-Pechora province the regional seal is the Upper Devonian Kynov-Sargayev argillite. In those places where this seal is not broken the main productivity is from lower occurring Middle Devonian clastics and Ordovician-Silurian-Lower Devonian carbonates. These pools are overpressured.
Rupture of the regional seal by faults in Timan-Pechora province has led to increase in stratigraphic range of oil-gas occurrence. Very important here are structure-forming and neotectonically active deep faults, and the combination of these two created very favorable conditions for traps. Also favorable is a system of pre-Paleozoic faults that were repeatedly rejuvinated during deposition of the platform cover. The young Cenozoic system of faults has not created structures but has contributed to enhancing permeability. The largest fields, commonly overpressured, occur in zones of intersection of the pre-Paleozoic and Cenozoic fault systems. These same zones have greater stratigraphic range of productivity on up to the Triassic. In some fields the volume of hydrocarbons in the Silurian-Lower Devonian is many fold less than in the overlying Permo-Carboniferous.
Within the Timan-Pechora province as a whole productive structures with overpressure are associated with high-displacement faults that bound mega-arches and also with sites of intersection of these faults with younger faults.
The association of overpressure with faults is found also in West Siberia. For example, the Yamal-Tazov zone of structures, where the pools are overpressured, is associated with a node of intersection of the Omsk zone of faults of Paleozoic inception with the regional, tectonically active Aralo-Khatanga fault. On the Salym and Krasnoleninsk groups of structures the overpressure is related directly or indirectly to very old structure-forming faults that have been successively rejuvinated on up to the present.
High-pressure yields of fluid reaching 3500 bbls a day have been recovered in the West Omsk and East Omsk fault zones, which are associated with the Yamal-Pur aulacogen. In overpressured zones of the Triassic-Jurassic complex fluids have migrated upward not only from the lower part of the Mesozoic but also from the pre-Mesozoic. Both anomalously high and low pressures have been recorded within the same structure. Commercial flows of overpressured hydrocarbons recovered from Riphean-Paleozoic rocks in Novoport field on the Yamal Peninsula and also on several structures of the Krasnoleninsk arch and in the Khanty-Mansiysk and Festival areas of the East-West Ob region indicate that the lower part of the sedimentary cover is very favorable for discovery.
Taken from Ulybin and Trunov, 1992; digested in Petroleum Geology,
vol. 28, no. 3/4, map showing faults and overpressure zones.
Copyright 2001. You are encouraged to print out this News Letter and
to forward it to others. Earlier News Letters are available at:
http://geocities.com/internetgeology/
This News Letter is distributed without charge in the interest of our
science of petroleum geology. To be added to the mailing list, please
send your e-mail address to: jamesclarke@erols.com
For information on the journal Petroleum Geology please telephone
703 759-4487 or FAX 703 759-3754.