Petroleum geology of the West Siberian Basin and a detailed description of the Samotlor oil field

Abstract

The major drainage is northward. Long, wide, deep rivers which meander across the vast marshy and forested, lake-strewn plain to the Arctic Ocean. The coastline is irregular, broken by long embayments and numerous close islands. Soils and vegetation. Three distinctive zones are present: (1) North of the Arctic Circle, highly organic soils of peat over sand and clay are widespread and are especially thick along rivers. North of about 72°N, Arctic barrens have only spotty turf of dwarf grass, herbs, and lichens less than a foot tall and scattered shallow peat bogs. Southward, grassland, grassy tundra, and dense scrub tundra also include scattered shallow peat bogs. (2) South of the tree line, which is near the Arctic Circle, to the latitude of Tyumen and Tomsk, very deep sand, clay, and peat soils support dense evergreen and deciduous taiga forest. Numerous peat bogs with thick peat over sand and clay also characterize this zone. (3) In the southernmost areas, cropland with patches of forest and fields of grass are common on deep to very deep fine-grained soils. A few areas of very deep sand are also present. Permafrost. Permafrost occurs in much of the area north of about 60°N in three zones: (1) North of the Arctic Circle, permafrost is mostly continuous and generally more than 200 m thick; the active layer is only .5-1.0 m thick. In places, the permafrost is more than 600 m thick. Along river valleys, the thickness of permafrost decreases. (2) From the Arctic Circle south to about 62°N, permafrost is not continuous, but commonly there are two layers of permafrost separated by unfrozen ground (talik). The upper (Recent) permafrost layer ranges from 10-100 m in thickness and the talik from 10-50 m. The top of the lower (Pleistocene) permafrost occurs at depths of 80-200 m, and extends down to 200-300 m below the surface. (3) Between 62°N and 60°N, only Pleistocene permafrost is present, the top is generally 150-200 m below the surface and its thickness is 100-200 m. In much of West Siberia, especially in areas with permafrost, icings (masses of surface ice formed in winter by freezing of groundwater seepage) are common, and they may attain a thickness of 10 m, cover several kilometers, and remain unthawed for several years. Drainage characteristics. Riverflow regime and ice regime vary considerably from north to south. In most of the area, high water, ice jams, and extensive flooding occur from May to August or September. Floods rise as much as 20 m in the lower Yenisey River and extend over 48 km in width in the lower Ob f River. Large areas are more than 50 percent lake covered part of the year. Most rivers and lakes have 2 m of ice or are frozen solid from early December to late March and those in the extreme north freeze in October. The southernmost areas have interior drainage. Many streams and lakes are intermittent, having an abrupt rise after snowmelt in May and a swift fall in late May or mid-June. Many lakes are saline. Ice cover of less than one meter is common from early December to April or May. Clima...

Radioisotopic, Culture-Based, and Oligonucleotide Microchip Analyses of Thermophilic Microbial Communities in a Continental High-Temperature Petroleum Reservoir

“…The Samotlor oil field, as well as all oil fields of the Middle Ob region, occurs in an area that, in the late Jurassic and early Cretaceous, was intermediate between a vast alluvial deltaic plain and a marine basin where prodelta deposits accumulated extensively (10). The existence of thermophiles, including marine organisms, in this deep location, thousands of kilometers from all volcanic areas and hundreds of kilometers from the nearest ocean, suggests that they were deposited with the original sediment and survived over geological time.…”

“…The Samotlor oil field (60°ЈN, 80°ЈE) is located in the middle Ob region in the vicinity of Nizhnevartovsk (Western Siberia, Russia). Geologically, this field is a typical representative of the largest oil fields of the world with respect to reservoir rock (sandstone), trap type (anticlinal), age of reservoir rock (mainly Lower Cretaceous and Upper Jurassic oil-bearing formations), average depth (between 1,700 and 2,450 m), and depositional environment (shelf or shallow marine) (10). Oil-producing wells studied in this work were located in an area of 6 km 2 , the distance between neighboring wells ranging from 0.2 to 0.5 km.…”