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The AAPG/Datapages Combined Publications Database
AAPG Bulletin
Abstract
AAPG Bulletin, V.
2015. The American Association of Petroleum Geologists. All rights reserved.
DOI: 10.1306/02091514125
Origin and accumulation of CO2 and its natural displacement of oils in the continental margin basins, northern South China Sea
Baojia Huang,1 Hui Tian,2 Hao Huang,3 Jihai Yang,4 Xianming Xiao,5 and Li Li6
1Research Institute, Zhanjiang Branch of China National Offshore Oil Corporation Ltd., Zhanjiang 524057, China; present address: State Key Laboratory of Organic Geochemistry, Guangzhou Institute of Geochemistry, Chinese Academy of Sciences, Guangzhou, Guangdong 510640, China
2State Key Laboratory of Organic Geochemistry, Guangzhou Institute of Geochemistry, Chinese Academy of Sciences, Guangzhou 510640, China; [email protected]
3School of Petroleum Engineering, China University of Petroleum, Beijing 102249, China
4Exploration Department, Zhanjiang Branch of China National Offshore Oil Corporation Ltd., Zhanjing 524057, China
5State Key Laboratory of Organic Geochemistry, Guangzhou Institute of Geochemistry, Chinese Academy of Sciences, Guangzhou 510640, China
6Research Institute, Zhanjiang Branch of China National Offshore Oil Corporation Ltd., Zhanjiang 524057, China
ABSTRACT
Many -rich (up to 97% by volume) natural gas pools have been found in the continental margin basins of the northern South China Sea. By combining the geochemical data from 53 samples with their geologic backgrounds, this study investigated the origins and accumulation mechanism of
, and discussed the role of
in driving oil as it charged the reservoirs. The results reveal that the
gases in the Yinggehai basin originate mainly from the thermal decomposition of both Miocene calcareous shales and Paleozoic carbonates, and that
from mantle degassing is only a minor contributor. The
accumulations in the Yinggehai basin are mainly controlled by diapiric faults and episodic thermal fluid movements. The
gases in the eastern Qiongdongnan and western Pearl River Mouth basins are mainly related to magmatic or mantle degassing, and the volatiles from magmatic degassing during the igneous intrusion stage are the most likely major source of
in these reservoirs, with basement faults providing pathways for upward
migration
of
-rich mantle fluids. Natural displacements of oil by
appear to be common in the eastern Qiongdongnan and western Pearl River Mouth basins. The
-flooded oil or gas reservoirs have two common features that the present
gas pools or oil-bearing structures have residual oils representing prior charge, and are close to the basement faults that provide pathways along which the mantle-derived
-rich gas was migrated. The oils from prior hydrocarbon reservoirs have been naturally driven out by
to form secondary oil reservoirs in the eastern Qiongdongnan and western Pearl River Mouth basins. Therefore, a full understanding of the origin and distribution of
cannot just be used to trace hydrocarbon
migration
pathways, but also provide useful information for risk assessment prior to drilling.
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