As the biggest oilfield discovered offshore China so far，the Penglai 19-3 oilfield has aroused constant debates on oil sources and characteristics of massivescale hydrocarbon accumulation in the late stage.From this study，we have brought up with three new understandings.First，oil in the Penglai 19-3 oilfield mainly originates from the source rocks in the Shahejie Formation and partially from source rocks in the Dongying Formation (in the Bozhong sag).Hydrocarbons charged reservoirs from two apparent directions，i.e.

the NW direction (from the Bozhong sag) and the SE direction (from the Miaoxi sag).The favorable factors for the development of the Penglai 19-3 oilfield are extremely abundant oil source in the Bozhong sag，longexisting lowpotential energy area and the energy release from the TanLu Fault as well as favorable carrier system dominated by unconformities.Third，The significant differences of interwell temperature，change patterns of oil density，viscosity and gases and largescale existence of “gas chimney” rooted in ocean floor reveal that this oilfield is obviously characterized by abundant hydrocarbon sources and late hydrocarbon accumulation.Oil charging is still intensive in the northern part of the field at present.All leads to the conclusion that the Penglai 19- oilfield is a typical massivescale，rapid hydrocarbon accumulation in the late stage in Bohai Sea. Key words： biomarker compounds

TanLu Fault

gas chimney

Neogene oil pool

hydrocarbon accumulation in the late stage

Penglai 19-3 oilfield

Bohai Sea New understandings of hydrocarbon accumulation in Penglai 19-3 oilfield

the Bohai waters Guo Yonghua

Zhou Xinhuai

Ling Yanxi

Li Jianping

Wang Feilong and Wang Jun (Exploration & Production Research Institute

Bohai Oilfield

CNOOC Tianjin Company

Tianjin 300452

China) As the biggest oilfield discovered offshore China so far，the Penglai 19-3 oilfield has aroused constant debates on oil sources and characteristics of massivescale hydrocarbon accumulation in the late stage.From this study，we have brought up with three new understandings.First，oil in the Penglai 193 oilfield mainly originates from the source rocks in the Shahejie Formation and partially from source rocks in the Dongying Formation (in the Bozhong sag).Hydrocarbons charged reservoirs from two apparent directions，i.e.

the NW direction (from the Bozhong sag) and the SE direction (from the Miaoxi sag).The favorable factors for the development of the Penglai 19-3 oilfield are extremely abundant oil source in the Bozhong sag，longexisting lowpotential energy area and the energy release from the TanLu Fault as well as favorable carrier system dominated by unconformities.Third，The significant differences of interwell temperature，change patterns of oil density，viscosity and gases and largescale existence of “gas chimney” rooted in ocean floor reveal that this oilfield is obviously characterized by abundant hydrocarbon sources and late hydrocarbon accumulation.Oil charging is still intensive in the northern part of the field at present.All leads to the conclusion that the Penglai 19-3 oilfield is a typical massivescale，rapid hydrocarbon accumulation in the late stage in Bohai Sea.