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Abstract

AAPG Bulletin, V. 88, No. 1 (2004), P. 115-125.

Copyright copy2004. The American Association of Petroleum Geologists. All rights reserved.

Mesozoic source rocks and petroleum systems of the northeastern Qaidam basin, northwest China

Yongtai Yang,1 Baomin Zhang,2 Changyi Zhao,3 Tianguang Xu4

1Department of Geology, University of Toronto, Toronto, Ontario, M5S 3B1, Canada; [email protected]
2Research Institute of Petroleum Exploration amp Development (RIPED), Beijing 100083, China
3Research Institute of Petroleum Exploration amp Development, Beijing 100083, China
4IHS Energy, Houston, Texas 77056; [email protected]

AUTHORS

Yongtai Yang is a Ph.D. candidate at the University of Toronto, studying sequence stratigraphy and basin analysis. He received an M.S. degree in geology from the China Research Institute of Petroleum Exploration amp Development (RIPED) in 1996. He worked as a petroleum geologist at RIPED from July 1996 to July 2003.

Baomin Zhang received his M.S. degree in geology from the Beijing Normal University in 1989. He currently is a senior geologist focusing on sedimentology and petroleum geochemistry at RIPED. Before joining RIPED in 1994, he worked as an associate professor at the Beijing Normal University.

Changyi Zhao received his Ph.D. in geology from the Chinese University of Mining and Technology in 1991. He currently is a senior geologist focusing on petroleum geochemistry and petroleum geology at RIPED.

Tianguang Xu received his M.S. degree in geology from Kansas State University in 2001. He is currently a basin researcher with IHS Energy, focusing on Chinese basins.

ACKNOWLEDGMENTS

Support for this research was provided by the Chinese Important Basic Research and Development Plan "973" (2001CB209100). We are grateful to PetroChina for permission to publish this paper. Andrew Miall's review greatly improved this paper. Bradley Ritts provided more meaningful discussion and suggestion.

ABSTRACT

The Qaidam basin is a continental petroliferous basin located in northwest China. Its northern sector is an important hydrocarbon province, where one of the earliest oil discoveries in China was made. Although Mesozoic source rocks are understood to be important parts of Qaidam petroleum systems, the identification and distribution of Mesozoic source rocks in the subsurface are poorly understood. Middle Jurassic coal measures and associated shales have long been considered to be the primary Mesozoic source rocks for the northeastern Qaidam basin without any support from subsurface geochemical and geological data. However, new data have been gathered from earlier Mesozoic sediments that were penetrated by the Lengke-1 well, a deep scientific well with a total depth of 5200 m (17,060 ft). The well was drilled on the Lenghu structural belt in 1997 and documented other effective source rocks. Geochemical analyses indicate that Lower Jurassic mudstones are good to excellent source rocks for the commercial oil wells in the Lenghu area. The upper Middle Jurassic shales are very good source rocks for the commercial oil wells in the Yuka area. Two source rock intervals in the northeastern Qaidam basin allow for two petroleum systems to be distinguished, the Lower Jurassic–Lower Jurassic/Tertiary and Middle Jurassic–Upper Jurassic. The Lower Jurassic–Lower Jurassic/Tertiary petroleum system, with a geographical extent of 15,000 km2 (5800 mi2) and a cumulative amount of source rocks between 200 and 700 m (650 and 2300 ft), represents a favorable target for future exploration. The Middle Jurassic–Upper Jurassic petroleum system, however, may have a lower exploration potential because of a smaller area (1500 km2 [580 mi2]) and a thinner cumulative amount of source rocks (100–200 m [330–650 ft]).

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