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.
