The Timan-Pechora Basin Province of Northwest Arctic Russia:  Domanik Paleozoic Total Petroleum System

Sandra J. Lindquist

preference, and a maximum near C15; d13C for saturates and aromatics = -31; hopanes C29 < C30; and high tricyclics (Abrams and others, 1999).

Offshore oils possibly from marine to marginal-marine Triassic source rocks have variable geochemical and isotopic signatures (Zakharov and Kulibakina, 1997). Rare, shallow gas occurrences in Triassic reservoirs of the Pechora-Kolva Aulacogen are biogenic in origin (Pairazian, 1993).

Migration Paths and Petroleum System Size

The Timan-Pechora Basin Province contains 20 BBOE known ultimate recoverable reserves, 29% produced through 1995 (Petroconsultants, 1996). Sixty-six percent is oil (13.157 BB, 25% produced), 30% is gas (36.535 TCF, 34% produced), and 4% is condensate (716 MMB, 51% produced). Approximately 5% of the reserves are in 6 fields that were mixed with or perhaps entirely sourced from petroleum systems (Triassic, Siluro-Ordovician) other than the Devonian Domanik (Table 1).

Migration paths are not exceptionally long because the primary Devonian source rock is present and at oil- or gas-stage maturity over most of the onshore area. Direct charging occurs laterally from the source rock into coeval reservoir rock, as well as by vertical migration through strata and along faults. Remigration occurred with repeated tectonic activity (Dedeev and others, 1994). Potential southward updip migration of Triassic-sourced hydrocarbons from the South Barents Basin required long distances of travel, likely assisted through NW and NE trending fault systems (Oknova, 1993). Paleozoic carbonates and sandstones are the major Timan-Pechora reservoirs (Table 2).

Geographic and Stratigraphic Location
     Major Source Rock
The primary source rocks ("Domanik," Figure 3 and Figure 6) of the Timan-Pechora Basin Province are organic-rich, basinal facies equivalents of shelf-edge reefs. Late Devonian (Frasnian) source rocks constitute the largest area, although similar depositional conditions existed in more areally restricted depocenters through earliest Carboniferous (Tournaisian) time (Ulmishek, 1988; Alsgaard, 1992) and again in different basin centers during Early Permian time. The Frasnian depositional basin was extensive in a N-S direction from the region of the Caspian Sea in west Kazakhstan and southwest Russia, northward an unknown distance offshore into the
Pechora Sea (southern Barents Sea). Sapropelic to humic organic matterhas been documented for non-Domanik Devonian through Triassic rocks on Kolguyev Island (Bro and others, 1990). Old aulocogen borders likely had some influence on where the abrupt facies changes occurred from shelf carbonates to basinal-equivalent facies. Paleozoic deep basinal facies are absent in  the northern Izhma-Pechora Depression and questionable in the easternmost foredeep area of the province near the junction of the Pay-Khoy Ridge with the Ural Mountain trend (Ulmishek, 1988) (Figure 1). Basinal facies are absent in large portions of the Khoreyver Depression.

     Other Source Rocks

Possible Siluro-Ordovician source rocks are presumed to exist in the eastern part of the province (Adzva-Varandey Zone, Kosyu-Rogov foredeep basin), associated with known local evaporites. Triassic and Jurassic source rocks are also present north of this province in the Barents Sea basins, and Triassic-sourced oil and gas has charged some northern Timan-Pechora reservoirs (Zakharov and Kulibakina, 1997; Kuranova and others, 1998). Jurassic source rocks are thin (few tens of meters, Oknova, 1993) and thermally immature at the closest proximity to the offshore portion of the Timan-Pechora province.

Thickness, Lithology and Depositional Environment

Domanik source rocks are basinal facies equivalents of shelf-edge reefs and are composed of thin-bedded, dark-colored siliceous shales, limestones and marls with calcareous, siliceous, phosphatic and pyritic concretions. They were deposited in 100-400 meter water depths under reducing conditions with restricted circulation and low sedimentation rates during a eustatic highstand (Alsgaard, 1992; Abrams and others, 1999). Algal content is high. Thicknesses range from a few tens to 500 meters (Shimansky and others, 1995), and abrupt facies and thickness variations document the presence of active graben systems during deposition. Western provenance and an eastward monoclinal tilt to the basin caused the western shelf edge to prograde eastward through time (Ulmishek, 1988). In contrast, reefs on the eastern (West Ural) basin margin were aggradational in character. Few pinnacle or patch reefs developed in the depositional system.

Geochemistry of Source Rock(Continued on Next Page)

     Major Source Rock
Domanik (middle Frasnian) source rocks contain sapropelic, type I and type II organic matter with TOC (total organic carbon) content ranging from 1-30 wt %, but more typically averaging around 5 wt % (Alsgaard, 1992;

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U. S. Geological Survey Open-File Report 99-50G