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Origin of Gas of Giant Gas Fields of North of West Siberia
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        "James Clarke" <jamesclarke@erols.com>
together, in 2000, the seven leading majors 
LUKoil, Yukos, SNG, TNK,
Tatneft, SIBNEFT and Rosneft 
accounted
  for over 64 percent of Russia's explored oil
reserves, nearly 75 percent of oil well
stock, over 72 percent of oil production,
nearly 54 percent of refinery runs and
almost 71 percent of total crude oil
                    exports to the "far abroad."
Origin of Gas of Giant Gas Fields of North of West Siberia
Internet Geology News Letter No. 109, August 6, 2001

     The north of West Siberia is an extremely important gas-producing  region, playing a substantial role in the energy balance of the world.   It holds first place in the world in abundance of reserves, and in number  of unique, giant, and large fields.  Gas resources as of 1993 were  assessed at 100 trillion cubic meters (3,500 tcf) and proved reserves  of commercial catagories at 50 trillion cubic meters (1,750 tcf). 

     All these gas pools within the thick (up to 2000 m) Cretaceous   Neocomian-Cenomanian oil-gas complex are in its upper part in  Cenomanian sediments at depth of 400 to 1200 m directly beneath  the Turonian-Paleogene regional clay seal. They occur at crests of  highs that have closures of 100-200 m and more. The crest areas of  these highs are large at 500 to 4000 sq km. 

     The continental sand-silt Cenomanian complex is a hydrodynamic  unit.  The pools have a massive-blanket character and have practically  horizontal gas-water contacts.  The gas is 99 percent methane and  contains up to 0.3 percent ethane, propane, and butane.  Traces of  condensate are present.  Oil rings have been found in some fields;  this oil is heavy, viscous, and contains some sulfur. 

     During the time from the Valanginian to the Cenomanian the north  of West Siberia  experienced largely continental conditions that were  favorable for deposition and preservation of plant matter.  There were  individual times of maximum coal accumulation that led to formation  of coal beds.  The number of coal beds in most wells is 10-30, and  their aggregate thickness is in tens of meters.  Also present are  enormous masses of disseminated coaly material in the form of  seams and lenses in various lithologic varieties.  The Pokur Series  of Aptian-Cenomanian age is a typical coal-bearing complex. 

     A warm humid climate and rapid development of plant life  prevailed  throughout all of the Early Mesozoic and Cenomanian  in the study area.  The carbon isotopic composition of the gases  in these fields exhibits an elevated content of the "light" isotope C-12.   There is an exceptional similarity between the gases of the study  area and those of modern swamps, indicating that their formation  was under conditions similar to those of modern swamps. 

     Processes of coalification are accompanied by generation  of carbon dioxide along with methane.  It is estimated that with  increase in degree of coalification from the brown-coal stage to  anthracite the amount of methane generated by one ton of coal  increases from 68 to 287 cubic meters whereas the amount of carbon dioxide decreases.  It is proposed that since at the  brown-coal stage of catagenesis of the organic matter of the  Pokur Series methane was generated in subordinate quantities  in comparison with carbon dioxide, most of thje methane of the  Cenomanian gas could have formed as a result of bacterial  reduction of carbon dioxide. 

Taken from Nemchenko, Rovenskaya, and Schoell, 1999;   digested in Petroleum Geology, vol. 35, no. 3, p. 244-258, 2001;   eight tables of data and one large cross section.

Copyright 2001 James Clarke.  You are encouraged to print  out this News Letter and to forward it to others.  Earlier News  Letters are available at our web page: 
 

About the Author and Publisher

Dr. James Clarke was born in Tennessee and grew up in Georgia.  His higher education was interrupted by World War II, in which he was a Combat Infantryman in the 99th Division.  Among other decorations he received the Belgium Croix de Guerre.

He received the B. A. from Emory University in 1947 and the Ph. D. from Yale University in 1950.  His dissertation was under Dr. Adolph Knopf.  From 1950 to 1959 he was a professor of geology at Vanderbilt University, University of South Carolina, and Duke University.

Clarke joined the United States Geological Survey in 1959 and was project chief of the group that prepared Geophysical Abstracts, Abstracts of North American Geology, and Bibliography of North American Geology, until these publications were discontinued in 1970.  For the next seven years he conducted field mapping of sedimentary, igneous, and metamorphic rocks in the Appalachian region.

In 1977 Clarke became an initial member of the USGS World Energy Resources Program and continued with this group until his retirement in 1991.  His major assignment was the preparation of regional and detailed studies of petroleum basins of the Soviet Union.  He has published more than 70 scientific papers.  Since his retirement he has continued his association with the Survey as a volunteer.

Since 1958 Clarke has published "Petroleum Geology", which is a digest in English of Russian language articles on petroleum geology.  This journal is published privately on a non-profit basis in the interest of our science.  He also responds to requests for consultation.

In March of this year Clarke was honored by the Special Award of the American Association of Petroleum Geologists for his contributions to the field of petroleum geology.
Mud Volcanoes of South Caspian Depression, 
Internet Geology News Letter No. 83, February 5, 2001 

     Mud volcanoes are associated with the Alpine-Himalaya fold belt from northern Italy on the west to New Guinea on the east. 
The most significvant of these are on the south of the Greater 
Caucasus in Azerbayjan and in the South Caspian depression.
More than half the mud volcanoes of the world are concentrated in the South Caspian depression, and this does not even take into account those in the deep-water part of the Caspian Sea. 


Afghan-Tadzhik depression Petroleum Geology of Tuapse  Arctic Petroleum Potential Russian Offshore  Astrakhan Arch North SW Caspian Devonian Clastic
Barents Sea Jurassic Petroleum Potential Barents-Kara Shelf Oil-Gas Potential Continental Margin Basins of Barents Sea

BASHKORTOSTAN (BASHKIRIA) Petroleum Prospects  Black Sea
Tuapse


Petroleum Potential of Black Sea and Sea of Azov, July 17

Mud Volcanoes in Black Sea Internet Geology News Letter No. 50. June 19, 2000 Buzuluk Depression Chukchi Sea Petroleum Potential
Dnieper-Donets Depression Lower Carboniferous Plays Domanikites - Bituminous Sedimentary Rocks 
Domanikites
Tataria
Bashkortostan
Romashkino


Salt Accumulation in North Caspian Depression,  Caspian Depression North Plate Tectonic Development Caspian Depression South Pliocene Delta in Eastern Part
Caspian depression North Salt-Related Traps Caspian Depression North Carbonate Massif Dauletabad-Donmez gas field European Craton East Source Beds


Fergana Intermontane Petroleum Potential
Kamchatka West Tertiary Section of Kolpakov downwarp Kamchatka Cooperative economics needed to tap stranded gas 
Laptev Sea Ust'-Lena Downwarp SE
Orenburg Region Hydrocarbon Systems of Devonian Clastics of South of Buzuluk Depression, Russia Okhotsk Sea Region Deltaic Deposits Pechora Sea Oil-Gas Potential Precambrian Reefs Siberia East Oil and Gas Pools Capillary-Sealed Siberian Craton Middle Paleozoic Salt  Siberia West Rifting Siberia West Clinoforms
Siberia Petroleum Habitat WesternVerkhoyansk Region Siberia West Cenozoic Tectonics ? Hydrocarbon Phase Differentiation,  Jurassic Potential of West Siberia
Recent Tectonics, Sea Level,  Climate Oil-Gas Deposits of West Siberia Volga-Ural Province Hydrocarbon Potential of Upper Proterozoic Rocks of Volga Region Mid Paleozoic Channel Deposits  Timan-Pechora Oil-Gas Basin


TempJu LK 
AmuDarya Bsn





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