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The AAPG/Datapages Combined Publications Database
Journal of Petroleum Geology
Abstract
Journal of Petroleum Geology, vol.
GEOLOGY AND GEOCHEMISTRY OF SOURCE
ROCKS
IN THE QAIDAM BASIN, NW CHINA
Jin Qiang1*, Zha Ming1, Liu Zhen2,
Gao XianZhi2, Peng Dehua3 and Lin Lamei1
1 University of Petroleum, Dongying, Shandong 257061, China.
2 University of Petroleum, Beijing, 102200, China.
3 Exploration and Development
Institute, Qinghai Oil Co. Ltd, Dunhuang, Qinghai,
736205, China.
*corresponding author : [email protected]
In this paper, we discuss the organic geochemistry of source
rocks
in the Qaidam
Basin, NW China, using data generated during a recent four-year study. This study
addressed some basic problems concerning petroleum systems in the basin, problems
which persist despite some five decades of exploration. We show that three separate
source
rocks
are present and these are distinct in terms of both age and depositional facies and
also geographical distribution.
The oldest source
rocks
are Lower Jurassic fresh-water lacustrine deposits which are
generally confined to northern Qaidam.These are currently thermally mature or highly
mature and have generated the oils, condensates and gases which have been discovered
in Jurassic and Tertiary
reservoirs
in the North Qaidam area.
By contrast, Tertiary source
rocks
were deposited in saline lakes. Previous studies
have shown that they are characterized by low TOC values (0.2-0.6%). However, we found
Tertiary
source
rocks
with TOC >1.0%; these were deposited in hypersaline lakes around
the Manya Depression in western Qaidam. These
source
rocks
have probably generated
the oils at fields recently discovered in the western part of the basin.
The youngest (gas-prone) source
rocks
in the basin are Quaternary. These were
deposited in saline lakes in the east and central parts of the basin and are thermally
immature. However they are thought to have generated the large volumes of biogenic gas
which are present in Quaternary
reservoirs
.
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