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The AAPG/Datapages Combined Publications Database
AAPG Bulletin
Abstract
AAPG Bulletin, V.
2007. The American Association of Petroleum Geologists. All rights reserved.
DOI:10.1306/05210705161
Hierarchies of
overpressure
retardation of organic matter maturation: Case studies from petroleum basins in China


Fang Hao,1 Huayao Zou,2 Zaisheng Gong,3 Shigang Yang,4 Zhiping Zeng5
1State Key Laboratory of Petroleum Resource and Prospecting, China University of Petroleum, Changping, Beijing 102249, People's Republic of China; present address: State Key Laboratory of Geological Processes and Mineral Resources, China University of Geosciences, Wuhan 430074, People's Republic of China; haofang@cup.edu.cn
2State Key Laboratory of Petroleum Resource and Prospecting, China University of Petroleum, Changping, Beijing 102249, People's Republic of China
3China National Offshore Oil Corporation, Beijing 100027, People's Republic of China
4State Key Laboratory of Geological Processes and Mineral Resources, China University of Geosciences, Wuhan 430074, People's Republic of China
5State Key Laboratory of Geological Processes and Mineral Resources, China University of Geosciences, Wuhan 430074, People's Republic of China
ABSTRACT
The effects of overpressure
on different aspects of organic matter maturation have been examined in three basins using multiple parameters.
Overpressure
in the Yinggehai Basin has retarded kerogen maturation,
hydrocarbon
generation, and thermal cracking of long-chain normal hydrocarbons, as well as evolution of isoprenoid hydrocarbons.
Overpressure
in the Dongpu depression, Bohai Bay Basin, seems to have retarded the maturation of bulk kerogens reflected by Rock-Eval Tmax, the thermal cracking of long-chain normal hydrocarbons, and the evolution of isoprenoid hydrocarbons, but seems to have had no detectable effects on vitrinite reflectance.
Overpressure
in the Qiongdongnan Basin has had no detectable retardation effects on all aspects of organic matter maturation. The observed phenomena suggest differential retardation of organic matter maturation (that is, different organic matter maturation reactions and different maturity parameters have been retarded by
overpressure
to different degrees in the same overpressured system) and four hierarchies of
overpressure
retardation. Hierarchy I retardation is defined as the state where the
overpressure
has retarded all aspects of organic matter maturation and is proposed to have been caused by the combination of high formation pressure and excess pressure, a high-water/organic matter ratio, and strong retention of reaction products in an early-developed, strong, persistent overpressured system. Hierarchy II retardation refers to the case in which all aspects of organic matter maturation except the maturation of hydrogen-poor kerogens, especially vitrinite, have been retarded and seem to have been caused by early-developed, moderate to strong, persistent
overpressure
. Hierarchy III retardation refers to the situation where
overpressure
has retarded only the thermal cracking of liquid hydrocarbons, but has had no detectable effect on the maturation of both hydrogen-rich and hydrogen-poor kerogens, and is proposed to have been caused by moderate to strong, persistent overpressures that began to develop around peak oil generation. Hierarchy IV retardation is defined as the situation where
overpressure
has had no detectable retardation on all aspects of organic matter maturation and may have been caused by cases wherein the
overpressure
developed too late, the intensity of the
overpressure
was too low, the duration of the
overpressure
was too short, or overpressured fluids had been expelled frequently. Resulting from both the diversities of organic matter maturation reactions and the complexities of
overpressure
generation and development, the hierarchies of
overpressure
retardation in different basins may be quite different, and it is necessary to use multiple parameters to understand the evolution of the petroleum systems in overpressured basins.
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