Relationship between abnormally high pressure and hydrocarbon accumulation of the Paleogene reservoirs in the northern part of central uplift,Dongpu sag,Bohai Bay Basin
Liu Jingdong1,2,Jiang Youlu2(1.Wuxi Petroleum Geolgogy Research Institute,Sinopec Exploration & Development Research Institute,Wuxi,Jiangsu 214126,China;2.School of Geoscience and Technology,China University of Petroleum,Dongying,Shandong 266555,China)
The Paleogene evaporation beds in the northern part of the central uplift in the Dongpu sag,Bohai Bay Basin,provide favorable conditions for the preservation of abnormally high pressure.Meanwhile,the complex faults provide passages for the release of the abnormally high pressure.These two factors make the dynamic process of hydrocarbon accumulation there so complicated that the relationship between the abnormally high pressure and hydrocarbon accumulation is still unclear at present.According to the measured data,we analyzed the vertical distribution of formation pressure in the Paleogene,restored the paleo-pressure by using the fluid inclusion method,discussed the hydrocarbon charging dynamics in the deep and shallow sequences,and built models of hydrocarbon migration and accumulation in this area.The following conclusions are drawn.(1) Vertically,there are 3 types of pressure systems in the study area,including normal pressure system,overpressure system and abnormally high pressure system.Wenmingzhai-Guyunji areas are dominated by the normal pressure system,Weicheng,Pucheng and Qiaobai areas by normal pressure and overpressure systems,while normal pressure,overpressure and abnormally high pressure systems are developed in the Wenliu area and its contacting area with the Weicheng and Pucheng areas.(2) The hydrocarbon charging system in deep sequences is of high pressure system or relatively high to high pressure systems.In contrast,the hydrocarbon charging system in the shallow sequences is dominated by episodic charging.(3) The hydrocarbon pooling models in the slope zone of the sag include lateral migration accumulation and indigenous accumulation,while those in the major part of the structure include vertical episodic migration and accumulation in the reservoirs above salt layers,inter-salt layer compound migration and accumulation,as well as vertical continuous migration and accumulation in the areas without salt layers.