<2H aline="center" Petroleum Geology of Siberian craton. Part I, Nepa-Botuobinsk
Part I. As of 1986 sixteen oil and gas fields had been discovered on the Nepa-Botuobinsk regional high of the Siberian craton. This feature has an area of 250,000 sq km. Elevations are up to 900 m above sea level, and relief is more than 500 m. Geological study of the region began in 1853-54 to the east in Vilyuy basin. Small-scale geological mapping started in 1935. Structures were mapped, and their oil-gas possibilities suggested. The first core drilling was in the Ust-Kut region in 1947. Geophysical surveys were begun in 1950. They were regional and not very effective. Some flows of oil and gas were recovered during the Fifties.
Success finally came in 1962 when Markovo stratigraphic well yielded a strong flow of oil from the Lower Cambrian. Intensive study of the Nepa-Botuobinsk region began in that same year. Exploration subsequently moved northward, and Yaraktino was discovered in 1970. In that same year the Srednebotuobinsk stratigraphic well became the discovery well for the field by this same name. By the beginning of the Seventies the geophysical surveys had shown clearly that several large arches were present in the region In 1975 the Nepa-Botuobinsk region was recognized as a single exploration target for Proterozoic Vendian and Lower Cambrian sediments.
By the beginning of 1985 a total of 503 deep wells had been drilled including 83 stratigraphic wells and 420 wildcat and delineation wells. A total of 60 structures and 12 other prospective areas had been outlined.
There has been a tendency to assign a new set of strati- graphic names in each newly discovered field. Three groups are generally recognized. The salt-bearing productive horizons of Cambrian age are assigned "A", the sub-salt carbonates of Vendian-Cambrian age are "B". and the underlying clastics of Vendian and Vendian-Cambrian age are "V". These are the transliterated first three letters of the Cyrillic alphabet.
Taken from Antsiferov and others, 1986; digested in Petroleum Geology, Vol. 23, no. 9/10; fourteen fields are described along with maps and cross sections. Part II. The enormous area of about 3.5 million sq km between the Yenisey River on the west and the Lena River on the east is the single ancient Siberian craton. The sedimentary cover of this craton differs from that of the Russian and other ancient cratons by its great stratigraphic completeness. For example, on the Russian craton after formation of a net of rifts in the Proterozoic Riphean-Vendian the region entered a long period with no sedimentary accumulation, whereas on the Siberian craton during this same time period largely carbonates more than 3 km thick were deposited. At the beginning of the year 2000 the hydrocarbon potential of the Siberian craton was assessed as 95 billion tons of oil equi- valent with possible recovery of 40 billion tons (280 BBOE).
Taken from Starosel'tsev, 2002; digested in Petroleum
Geology, Vol. 37 (Annual Volume), 1 map.
Copyright 2003 James Clarke. You are encouraged to print
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