Pathway System And Hydrocarbon Migration And Accumulation Of Buried Hill In Shulu West Slope,Jizhong Depression

Buried hill reservoirs are the main field of oil and gas exploration in the Bohai Bay Basin.With the development of exploration,it is of great scientific significance to summarize the laws of hydrocarbon migration and accumulation in buried hills for further exploration.Based on the comprehensive geological information,hydrocarbon geological data,geochemical data,geophysical data,test and analysis data and the previous research results,the oil and gas source,transportation system and oil and gas preservation conditions of buried hill reservoirs in Shulu sag were studied.In this paper,the types of reservoirs are divided,the geological characteristics and conditions of typical reservoirs are dissected,the main controlling factors of buried hill reservoirs are analyzed,the modes of hydrocarbon migration and accumulation in the study area are summarized,and the favorable accumulation areas are predicted.The results show that the physical property of buried hill crude oil is controlled by the burial depth,and there are three types of crude oil,the crude oil of slope buried hill is mainly derived from the relatively low mature Es₃^x source rock at the sag edge,and the crude oil of high-in-sag buried hill is mainly derived from the relatively high mature Es₃^xsource rock at the sag center.The transport systems of buried hills are mainly unconformity and fault.The oil and gas in the slope buried hills are accumulated in the reverse fault traps through unconformity lateral transportation,while the oil and gas can be directly injected into the high-in-sag buried hills due to the connection between source rock and reservoir through fault.The oil and gas migration simulations show that the structural ridges of unconformity and fault ridges have the function of collecting and dispersing oil and gas and regulating the migration direction,and have obvious control effect on the dominant migration and accumulation of oil and gas.The salinity of formation water from buried hills is generally low and can be divided into three types:I,II,and III.The oil and gas preservation conditions reflected by these three types gradually become better.The type of formation water has obvious influence on the physical properties of crude oil and reservoir distribution.The crude oil undergoes different degrees of water washing and biodegradation during the process of hydrocarbon migration and accumulation.And the weak alternating area and the discharge area are favorable zones for hydrocarbon accumulation in the study area where Type II or Type III formation water is distributed are favorable areas for hydrocarbon accumulation.Hydrocarbon accumulation in buried hills is controlled by four factors:source conditions,source-reservoir distance,transport system and preservation conditions,and two types of hydrocarbon accumulation modes are developed,namely,the near-source hydrocarbon accumulation in broken anticlinal trap transported by fault and the far-source hydrocarbon accumulation in fault block trap transported by unconformity.The law of oil and gas accumulation is the relatively rich accumulation of oil and gas in the areas with small source-reservoir distance,weak hydrodynamic force,good preservation condition and traps on the dominant migration path.In addition to the already explored buried hills in the high-in-sag area,the northern and southern of the slope are favorable areas for further exploration.