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AAPG Bulletin, Preliminary version published online Ahead of Print 15 November 2025.

Copyright © 2025. The American Association of Petroleum Geologists. All rights reserved.

DOI:10.1306/11062524045

Hydrocarbon accumulation processes and model controlled by overpressure evolution of the DF1-1 diapir in the Yinggehai Basin, South China Sea

Zonglin He1 , Fang Hao12 , Jinqiang Tian12 , Lin Hu4 , Gaowei Hu4 , Lu Yang12 , Shang Xu3 , and Qingfeng Meng3

1 State Key Labotatory of Deep Oil and Gas, China University of Petroleum (East China), Qingdao, Shandong, 266580, China
2 School of Geoscience, China University of Petroleum (East China), Qingdao, Shandong, 266580, China
3 Laoshan Laboratory, Qingdao, Shandong, 266237, China
4 Hainan branch of the China National Offshore Oil Corporation (CNOOC), Haikou, Hainan, 570311, China

Ahead of Print Abstract

The fluid diapir is formed through the upward intrusion of fluids along fracture zones, with hydraulic fracturing and fluid charge occurring at the uplift point of the overpressure interface. The DF1-1 diapir is the most typical fluid diapir in the Yinggehai Basin, characterized by multi-layer gas accumulation. In this study, petrography observation, laser Raman spectroscopy analysis, micro-thermometry, approximate calculation of fluid inclusion capture pressure and natural gas characteristics have been integrated to delineate the natural gas dynamic accumulation process and summarize the accumulation model of DF1-1 diapir. Results suggest that four-period natural gas with different composition have been documented. The first and second stage hydrocarbon gas-dominated charging occurred at 3.4-2.9 Ma and 1.8-0.4 Ma, respectively. The third and fourth acts of gas charging were dry gas and inorganic CO2, which occurred at 0.4-0 Ma. The paleo-pressure evolution of HL1 Formation was reconstructed following a model of “pressurization-release-pressurization”. And the coupling relationship between the Formation paleo-pressure evolution and the natural gas charge history was elucidated. Based on these analyses, this conformed to an overpressure-controlled episodic gas accumulation model, and the accumulation process can be summarized as follows: initially, gas accumulated in deep reservoirs, with formation pressure increasing to fracture pressure, leading to diapir opening and subsequent gas loss or adjustment to shallower reservoirs along diapir faults for further accumulation. Simultaneously, gas filled the reservoirs and episodic diapir activity in the later stages resulted in rapid gas charging. This process is the primary factor contributing to the heterogeneity of gas distribution.

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Please cite this AAPG Bulletin Ahead of Print article as:

Zonglin He , Fang Hao , Jinqiang Tian , Lin Hu , Gaowei Hu , Lu Yang , Shang Xu , Qingfeng Meng: Hydrocarbon accumulation processes and model controlled by overpressure evolution of the DF1-1 diapir in the Yinggehai Basin, South China Sea, (in press; preliminary version published online Ahead of Print 15 November 2025: AAPG Bulletin, DOI:10.1306/11062524045.

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