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Abstract

AAPG Bulletin, V. 88, No. 5 (May 2004), P. 613-625.

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

Geology and formation mechanism of late Quaternary shallow biogenic gas reservoirs in the Hangzhou Bay area, eastern China

C. M. Lin,1 L. X. Gu,2 G. Y. Li,3 Y. Y. Zhao,4 W. S. Jiang5

1Department of Earth Sciences, State Key Laboratory of Ore Deposit Research, Nanjing University, Nanjing, 210093, China; [email protected]
2Department of Earth Sciences, State Key Laboratory of Ore Deposit Research, Nanjing University, Nanjing, 210093, China; [email protected]
3Department of Earth Sciences, State Key Laboratory of Ore Deposit Research, Nanjing University, Nanjing, 210093, China; [email protected]
4Department of Earth Sciences, State Key Laboratory of Ore Deposit Research, Nanjing University, Nanjing, 210093, China; [email protected]
5Zhejiang Branch Company of PetroChina, Hangzhou, Zhejiang Province, 310013, China; [email protected]

AUTHORS

C. M. Lin received a B.Sc. degree from Daqing Petroleum Institute in 1986. He obtained his M.Sc. degree from the Petroleum University of China in 1995 and his Ph.D. from the Tongji University in 1997. Lin is currently an associate professor at the Department of Earth Sciences at Nanjing University, where he studies sedimentology and petroleum geology.

L. X. Gu received a B.Sc. degree from Peking University in 1967. He obtained his M.Sc. degree and his Ph.D. from Nanjing University in 1982 and 1985, respectively, and is currently a professor in the Department of Earth Sciences, Nanjing University. His principal research interests are the formation mechanism of oil and gas reservoirs in volcanic rocks.

G. Y. Li received a B.Sc. degree from Daqing Petroleum Institute in 1984. He is now a Ph.D. student in the Department of Earth Sciences at Nanjing University. Li's current research deals with the formation mechanism of gas reservoirs.

Y. Y. Zhao received her B.Sc. degree from Petroleum University of China in 2001 and is currently a M.Sc. student at Nanjing University. Her interest is now in the study of sedimentology.

W. S. Jiang received a B.Sc. degree in petroleum geology in 1958 from Peking Geology University. He has been working as a geologist with the Zhejiang Branch Company of PetroChina since then.

ACKNOWLEDGMENTS

This research is supported jointly by the China Natural Science Foundation (Project No. 40272063) and Zhejiang Branch Company, PetroChina. Y. H. Zhu and A. M. Xu of the Hangzhou-Bay Bridge-Building Company enthusiastically provided the authors with data. Thanks should be given to J. P. Bao, J. S. Qiu, D. D. Fan, and X. C. Lu and graduate students H. C. Zhuo et al., among others, discussions with whom greatly benefited the authors. The constructive suggestions of AAPG editors John Lorenz and Carol Christopher and reviewers improved the article. Special thanks should be given to Ronald C. Surdam and Zunsheng Jiao for editing and clarifying grammar and syntax. Editorial assistance by Paula Sillman is appreciated. It would have been almost impossible for the authors to finish this paper without such assistance.

ABSTRACT

Late Quaternary shallow biogenic gas reservoirs have recently been discovered and exploited in the coastal Hangzhou Bay area, northern Zhejiang Province, eastern China. The river in this area strongly incised the underlying old beds during a period of glacial maximum, which resulted in the formation of the Qiantangjiang and the Taihu incised valleys. These incised valleys were filled with fluvial sediments and buried by marine sediments during the postglacial period. Late Quaternary strata of the incised-valley area are composed of four sedimentary facies in ascending order: fluvial floor facies (IV), flood-plain facies (III), sublittoral-marine bay facies (II), and estuarine facies (I).

All commercial gas fields occur in flood-plain sand bodies of incised valleys. The bodies are buried 30ndash60 m (98ndash197 ft) deep and are 3.0ndash7.0 m (9.8ndash23 ft) thick, with a maximum thickness of more than 10 m (33 ft). They are surrounded by impermeable clays. Rapid deposition of overlying sublittoral-marine bay sediments supplied not only abundant gas sources, but also good preservation conditions. The main hydrocarbon sources are dark gray clays of the flood-plain facies and gray muds of the sublittoral-marine bay facies. Sediments of both facies have organic carbon content generally more than 0.4%. Shallow biogenic gas fields and deep gas fields require vastly different drilling and completion techniques. Drilling and completion costs are much lower for the biogenic gas fields.

Quaternary incised valleys and flood plains other than Hongzhou Bay in coastal areas of eastern China are promising targets of further exploration for shallow biogenic gas.

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