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AAPG Bulletin

Abstract

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Geochemistry of Oils from the Junggar Basin,

Northwest China

1

J. L. Clayton, J. Yang, J. D. King, P. G. Lillis, and A. Warden2

ABSTRACT

The Junggar basin of northwestern China is a structural basin containing a thick sequence of Paleozoic-Pleistocene rocks with estimated oil reserves of as much as 5 billion bbl. Analyses of 19 oil samples from nine producing fields and two oil-stained cores in the Junggar basin revealed the presence of at least five genetic oil types. The geochemistry of the oils indicates source organic matter deposited in fresh to brackish lake and marine environments, including coaly organic matter sources.

The volumetrically most important oil type 
discovered to date is produced from Late Carboniferous-Middle Triassic reservoirs in the giant Karamay field and nearby fields located along the northwestern margin of the Junggar basin. Oil produced from the Mahu field, located downdip in a depression east of the Karamay field, is from a different source than Karamay oils. Unique oil types are also produced from an upper Permian reservoir at Jimusar field in the southeastern part of the basin, and from Tertiary (Oligocene) rocks at Dushanzi field and Lower Jurassic rocks at Qigu field, both located along the southern margin of the basin.

Previous studies have demonstrated the presence of Upper Permian source rocks, and the possibility of Mesozoic or Tertiary sources has been proposed, but not tested by geochemical analysis, although analyses of some possible Jurassic coal source rocks have been reported. Our findings indicate that several effective source rocks are present in the basin, including local sources of Mesozoic or


©Copyright 1997. The American Association of Petroleum Geologists. All rights reserved.

1Manuscript received December 4, 1995; revised manuscript received December 2, 1996; final acceptance June 10, 1997.

2U.S. Geological Survey, Box 25046, Denver Federal Center, Denver, Colorado 80225.

3Research Institute of Exploration and Development, Karamay, Xinjiang, 834000, People's Republic of China.

The paper was significantly improved by reviews and comments of S. Creaney, K. Kelts, L. Snowdon, and the AAPG editorial staff. We appreciate constructive reviews of an earlier version of the manuscript by J. G. Palacas and J. R. Hatch, U.S. Geological Survey.

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