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Origin and accumulation of CO2 and its natural displacement of oils in the continental margin basins, northern South China Sea

Huang Baojia, Tian Hui, Huang Hao, Yang Jihai, Xiao Xianming and Li Li
Origin and accumulation of CO2 and its natural displacement of oils in the continental margin basins, northern South China Sea
AAPG Bulletin (July 2015) 99 (7): 1349-1369

Abstract

Many CO (sub 2) -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 CO (sub 2) , and discussed the role of CO (sub 2) in driving oil as it charged the reservoirs. The results reveal that the CO (sub 2) gases in the Yinggehai basin originate mainly from the thermal decomposition of both Miocene calcareous shales and Paleozoic carbonates, and that CO (sub 2) from mantle degassing is only a minor contributor. The CO (sub 2) accumulations in the Yinggehai basin are mainly controlled by diapiric faults and episodic thermal fluid movements. The CO (sub 2) 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 CO (sub 2) in these reservoirs, with basement faults providing pathways for upward migration of CO (sub 2) -rich mantle fluids. Natural displacements of oil by CO (sub 2) appear to be common in the eastern Qiongdongnan and western Pearl River Mouth basins. The CO (sub 2) -flooded oil or gas reservoirs have two common features that the present CO (sub 2) 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 CO (sub 2) -rich gas was migrated. The oils from prior hydrocarbon reservoirs have been naturally driven out by CO (sub 2) 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 CO (sub 2) cannot just be used to trace hydrocarbon migration pathways, but also provide useful information for risk assessment prior to drilling.


ISSN: 0149-1423
EISSN: 1558-9153
Coden: AABUD2
Serial Title: AAPG Bulletin
Serial Volume: 99
Serial Issue: 7
Title: Origin and accumulation of CO2 and its natural displacement of oils in the continental margin basins, northern South China Sea
Affiliation: China National Offshore Oil Corporation, Research Institute, Zhanjiang, China
Pages: 1349-1369
Published: 201507
Text Language: English
Publisher: American Association of Petroleum Geologists, Tulsa, OK, United States
References: 52
Accession Number: 2015-082043
Categories: Economic geology, geology of energy sources
Document Type: Serial
Bibliographic Level: Analytic
Illustration Description: illus. incl. sects., strat. cols., 2 tables, sketch map
N16°00'00" - N20°00'00", E107°00'00" - E113°00'00"
Secondary Affiliation: Chinese Academy of Sciences, Guangzhou Institute of Geochemistry, Laboratory of Organic Geochemistry, CHN, ChinaChina University of Petroleum, CHN, China
Country of Publication: United States
Secondary Affiliation: GeoRef, Copyright 2017, American Geosciences Institute. Reference includes data from GeoScienceWorld, Alexandria, VA, United States. Reference includes data supplied by American Association of Petroleum Geologists, Tulsa, OK, United States
Update Code: 201535
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