Geochemical Characteristics and Origin of Natural Gas in the Eastern Tarim Basin(I)

CHEN Jian fa; XU Yong chang; HUANG Di fan

Tarim Basin, located in the northwest China, is one of the largest basins in the world, which has not been well explored. In recent years the large scale of petroleum exploration in the basin has led to the discovery of a series of oil and gas fields, with an approximate 1∶1 ratio of oil to gas resource. This means that the natural gas resource is very important for the hydrocarbon resource in the Tarim basin. In this basin most of the discovered gases are condensate associated gas and oil associated gas. It is show by chemical components analysis that the content of hydrocarbon of the natural gases from this basin is mostly higher than 65%. The content of CO₂ is mostly less than 5%. The content of N₂ is mostly less than 10% and the N₂ in some gases reaches 25% to 35%. The C ₁/C ₂₊ ratios of gases from Tabei area show a generally decreasing trend from east to west.The content of N ₂ in gases shows generally Qincreasing trend from east to west.The carbon isotopic composition of methane becomes gradually lighter from east to west. All these may be responsible to the low palaeozoic source rock,of which maturity is generally becoming lower from east to west.

Geochemical Characteristics and Origin of Natural Gas in the Eastern Tarim Basin(I)

1. State Key Laboratory of Gas Geochemistry, Lanzhou Institute of Geology, Chinese Academy of Sciences, Lanzhou 730000, P. R. China

Received Date: 1999-07-04

Rev Recd Date: 2000-05-29

Publish Date: 2000-08-10

Key words:

Tarim basin /
natural gas /
source rock

Abstract: Tarim Basin, located in the northwest China, is one of the largest basins in the world, which has not been well explored. In recent years the large scale of petroleum exploration in the basin has led to the discovery of a series of oil and gas fields, with an approximate 1∶1 ratio of oil to gas resource. This means that the natural gas resource is very important for the hydrocarbon resource in the Tarim basin. In this basin most of the discovered gases are condensate associated gas and oil associated gas. It is show by chemical components analysis that the content of hydrocarbon of the natural gases from this basin is mostly higher than 65%. The content of CO₂ is mostly less than 5%. The content of N₂ is mostly less than 10% and the N₂ in some gases reaches 25% to 35%. The C ₁/C ₂₊ ratios of gases from Tabei area show a generally decreasing trend from east to west.The content of N ₂ in gases shows generally Qincreasing trend from east to west.The carbon isotopic composition of methane becomes gradually lighter from east to west. All these may be responsible to the low palaeozoic source rock,of which maturity is generally becoming lower from east to west.

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Geochemical Characteristics and Origin of Natural Gas in the Eastern Tarim Basin(I)

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