U.S. DEPARTMENT OF THE INTERIOR
U.S. GEOLOGICAL SURVEY
The Timan-Pechora Basin Province of Northwest Arctic Russia: Domanik – Paleozoic Total Petroleum System
|Table 2. "Reservoir
age" is the top of the reservoir interval reported by Petroconsultants
(1966). Forty-two percent of the known recoverable reserves cannot be allocated
easily to specific strata, based on available data, but pre-Hercynian upper
Paleozoic reservoirs (Middle to Upper Devonian and Lower Permian) apparently
account for the bulk of producible hydrocarbons. Ulmishek (personal communication,
1999) believes that productive capability from Middle Devonian siliciclastics
is significantly under-represented in the table and perhaps captured within
the "Upper Devonian" category. From the Petroconsultants allocatable
data, carbonates would outproduce sandstones 54% to 46% in known recoverable
Stratigraphic-pinchout and normal-fault traps were created as early as Ordovician time during the opening of the Uralian Ocean and then again with aulacogen formation or rejuvenation during the Devonian period (Figure 6). Some 150 m.y. of subsequent periodic structural inversion continuously created new structural traps, destroyed others, and impacted sedimentation patterns, culminating in the Hercynian and Early Cimmerian orogenies (Figure 3). The regionally varying times of hydrocarbon generation (Carboniferous to Jurassic) overlapped the Late Paleozoic to Early Mesozoic tectonic cycle of trap formation and destruction. Dedeev and others (1994) believe that just 2-3% of all generated hydrocarbons remain trapped in the Timan-Pechora Basin.
The first commercial Timan-Pechora oil discovery, Chib’yu field, with basal Frasnian (upper Devonian) Pashiy sandstone reservoirs, was in 1930. Two years later, heavy oil (19° API) was discovered at nearby shallow Yarega field in Middle Devonian sandstones, which have been exploited by shaft mining and steam injection since 1939. Yarega currently is the 6th largest field in the Timan-Pechora Basin Province with respect to ultimate recoverable reserves (Petroconsultants, 1996). In 1934, 240 km farther northeast near the town of Pechora, Yugid field was discovered with oil in Lower Carboniferous sandstones.
First commercial gas, also in Devonian sandstones, was discovered in Sed’yol field, near Ukhta, in 1935. The largest province gas field, Vuktyl, was discovered in 1964 in Paleozoic carbonates of the southern Ural foredeep and has nearly 18 TCF in original reserves (Meyerhoff, 1980). Seven fields exceed 0.5 BBOE in ultimately recoverable reserves (Petroconsultants, 1996), and they were discovered in the following sequence, listed by decreasing size: #1 Vuktyl, 1964; #2 Usa, 1963; #3 Vozey, 1971; #4 Kharyaga, 1977; #5 Layavozh, 1969; #6 Yarega, 1932; and #7 Kumzhinskoye, 1975.
Identification and Description (Continued on Next Page)
Timan-Pechora reservoirs range in age from Upper Ordovician to Triassic (Table 2, Figure 6) and cover most of the province except for the northern Izhma-Pechora Depression to the west. The largest volume of reserves is in Middle/Upper Devonian siliciclastics and Lower Permian carbonates. An early Paleozoic progression from limited continental to extensive marine depositional environments characterized the province, with a return to dominantly continental conditions by Late Permian and Triassic time. Offshore extensions of nearly all reservoir trends are underexplored.
Basal Ordovician siliciclastics are underexplored for deep structural and stratigraphic traps in what are now the Upper Pechora and Kosyu-Rogov foredeep basins and, if present, within the Khoreyver Depression. Ordovician through Lower Devonian reservoirs average 10-30 meters in net thickness and are mostly carbonates in structural and stratigraphic traps, focused in the southern Khoreyver Depression, the Adzva-Varandey Zone, and the Kosyu-Rogov Trough (Figure 1 and Figure 2b).
Middle Devonian reservoirs are all unconformity-encased sandstones of western provenance, with an isopach thick extending from the Upper Pechora Trough northward through the Pechora-Kolva Aulacogen (Ulmishek, 1982, 1988). They prolifically produce along sinuous trends where lithology changes – extending from the Omra Step, the southern Izhma-Pechora Depression and Upper Pechora Trough northward along the old Pechora-Kolva Aulacogen borders to a point south of the coastline (Figure 1). Facies are more marine eastward, and isopachs reflect pre-Late Devonian erosion within the Pechora-Kolva Aulacogen, where stratigraphic traps probably abound. Two fields are reported to produce from Middle Devonian strata within the Adzva-Varandey Zone (Petroconsultants,1996), although Ulmishek (personal communication, 1999)believes Middle Devonian strata to be absent there. Middle Devonian net reservoir thickness averages 13 meters, with a maximum of 114 meters.
Overall, Upper Paleozoic reservoirs are carbonates over sandstones by nearly 2:1 in volume of known ultimately recoverable reserves (Table 2). Net reservoir thicknesses average from 9 to 19 meters. Facies and play trends for these intervals are discussed and illustrated in Ulmishek (1982), Ulmishek (1988), Rostovshchikov and others (1991), Belyayeva (1992), Belyakov (1994), Zhemchugova and Schamel (1994), and Aleksin and others (1995). Tectonically controlled Upper Devonian and Lower Permian shelf-edge reefs comprise the most significant carbonate plays, and the Domanik source rock facies are the basinal age-equivalents to Upper Devonian reefs. Upper Devonian Devonian reservoirs occur in a similar area to Middle Devonian reservoirs – but with more abundance in the
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