Internet Geology News Letter No. 149, May 13, 2002

Prirazlom oil field is located on the shelf in the southeastern part of Pechora Sea 60 km northwest of Varandey in Nenets District of Arkhangel Region. The field was discovered in 1989 by wildcat well 1 at a depth of 3100 m at the crest of an anrticline. The well tested at 393 cubic meters (2800 bbls) of oil per day from Lower Permian-Upper Carboniferous bioclastic limestones after acid treatment.

The Prirazlom (which in Russian means "along a fault") structure on the top of the Permo-Carboniferous reservoir has the form of a drape over lower-occurring rocks. Its dimensions are 18.3 by 5.1 km, and the area within the -2547 m closed structure contour is 62.35 sq km. A complex series of northwest-trending faults has now been recognized in the southeast of the structure.

The pay zone consists of two carbonate reservoirs of different genesis, The upper highly porous reservoir (Stratum I) is composed of bioclastic limestone, which is overlain by Kungurian clays, It is subdivided into three strata: Ia, Ib, and Ic. The lower reservoir (Stratum II) consists of relatively dense Carboniferous limestone. Total thickness of Stratum I ranges from 43 to 85 m, and effective thickness is 42 to 85 m, Total thickness of Stratum II is 49.5 to 63 m, and effective thickness is 11.1 to 26.2 m.

The main oil reserves are in Stratum I, which has an average porosity of 15.6 to 21.7 percent. Average oil saturation is 77-95 percent. Seismic surveys show that Stratun Ia extends to the east beyond the area of the lowest closed structure contour. The question of its oil saturation to the east remains open. Within Stratum I the main reserves are in Ib, thickness of which increases toward the north.

Density of the oils ranges from 0.91 to 0.97. Hydrogen sulfide is present at 0.4 percent in the gas, and sulfur content of the oil is 2.3 percent.

Delineation drilling failed to determine the precise position of the water-oil contact for Strata I and II. Geological and geophysical data indicate that the water-oil contact in Stratum I is at -2528 m.

Reserves of oil in place of catagories C-1 and C-2 of Prirazlom field are placed at 295 million tons (2.065 billion barrels), and recoverable oil is assessed at 75.3 million tons (542 million barrels).

The field is to be developed from a single platform. Plans call for 55 wells, including 31 production wells. Of these there will be 15 horizontal wells with maximum reach of 5.5-6 km. Length of production is estimated at 20.5 years with a daily yield of about 16,000 tons (115,000 bbls). Recovery factor is estimated at 0.34. The oil will be transported by tanker to the Murmansk terminal.

Taken from Nikitin and Khvedchuk, 1997; digested in Petroleum Geology, vol. 31, no. 4, 1997. two maps and one stratigraphic section.
Copyright 2002 James Clarke. You are encouraged to print out this News Letter and to forward it to others. Earlier News Letters at available at: http://geocities.com/internetgeology/
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