More than 30 countries have recoverable heavy oil reserves. Four of the world’s largest oil fields, the supergiants Al-Burqān in Kuwait, Kirkuk in Iraq, Abū Saʿfah in Saudi Arabia, and the Bolivar Coastal field in Venezuela, contain and have produced very large amounts of heavy oil in addition to conventional oils. Other giant fields producing heavy oil include Zubair in Iraq; Duri in Indonesia; Gudao and Karamai in China; Seria in Brunei; Bacab, Chac, and Ebano-Panuco in Mexico; Belayim Land in Egypt; Maydan Mahzam in Qatar; and Uzen and Zhetybay in Kazakhstan.
One of the largest petroleum reserves in the world is a heavy oil field in the Orinoco Belt in eastern Venezuela. Although sometimes called a tar sand reserve, this enormous heavy oil deposit is nonbituminous. The U.S. Geological Survey has estimated that the recoverable heavy oil in this reserve, concentrated in a strip some 700 km (435 miles) long by 60 km (37 miles) wide along the Orinoco River, is around 513 billion barrels, though such recovery may not be economically viable.
California accounts for most of the thermally recovered heavy oil in the United States. The largest of the California heavy oil fields is Midway-Sunset, with an ultimate recovery estimated at more than 3 billion barrels. Almost as large is the Wilmington field, with about 3 billion barrels. The Kern River field, projected to ultimately produce slightly more than 2 billion barrels, and the South Belridge, with slightly less than 2 billion barrels of recoverable heavy oil, are the other top producing fields in the state.
Some heavy oil fields have been found to be associated with giant gas fields. These include the Bressay, Clair, and Ekofisk gas fields of the North Sea and the Russkoye gas field of Russia.
Tar sand deposits occur predominantly in the Western Hemisphere. Nearly three-quarters of the total world endowment of bitumen is estimated to occur in the Athabasca region of Alberta, Canada. Although some estimates place this bitumen reserve at 1.7 trillion barrels, only about 10 percent of the deposit is accessible by surface mining. Other significant Canadian tar sand deposits include the nearby Cold Lake and Peace River deposits. Additional bitumen is thought to be in Russia, mostly in the Volga-Urals and Siberian regions, and in Kazakhstan.
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