Geochemical Response Of Fluids And Rocks To Hydrocarbon Migration And Accumulation In Paleogene Of Dongying Depression

It is difficult to deduce the reservoir forming processes just based on organic geochemical index,because the reservoir in those areas experience multi-stages,multi-source hydrocarbon charging and with complexity later transformation.Formation water is the carrier of hydrocarbon fluids during reservoir forming process.In this process,there are a series of organic-inorganic interactions,and resulting in the changing of formation water and formation of diagenetic products.Those changes can be used to deduce hydrocarbon migration and accumulation processes.This paper pays mainly attention on Central uplift zone,Niuzhuang Sag,and Lijin Sag in Dongying depression.Based on geochemical characteristics of formation water,the source and evolution process of the formation water are both discussed.The differences of formation water in layers which with different oil content.Based on those researches,response characteristics of formation water to hydrocarbon migration and accumulation are determined.The study shows that there are three types of formation water in the Dongying Depression.The second type of formation water is the carrier of oil from Es₃x;third type of formation water is the carrier of oil from Es₄s.The oil-bearing layer in Ed-Es₂ has higher salinity and lower rNa/rCl compared to water layer in the same formation.The single indicator of Es₃-Es₄ showed no significant changes,and statistical software was needed to identify it.Based on geochemical characteristics of diagenetic products,the formation and evolution process of diagenetic products is also discussed.Relationships of hydrocarbon with formation water and diagenetic products are gained on the basis of the comparison between the formation water characteristics and diagenetic products of the oil and water layers.And the differences of the formation water and the diagenetic products in the different oilfields are studied,due to different source for them.Along the hydrocarbon migration pathways,this research also makes the changing of diagenetic products clear.The first type is atmospheric precipitation,which experienced evaporation and concentration,having no relationship with hydrocarbon accumulation;the second type is the semi salty-fresh lake water,which underwent diagenetic transformation and is related to the hydrocarbon from Es₃x source rocks;the third type is the saline lake water undergoing diagenetic transformation,which is related to hydrocarbon from Es₄s source rocks.There are 3 types of authigenic kaolinites in the study area.The first type is diagenetic products of atmosphere infiltration,which has nothing to do with hydrocarbon migration and accumulation;the second is the product of organic acid,which is partly related to hydrocarbon;the third kind is the result of organic CO₂,is the diagenetic product of hydrocarbon fluids.There are 4 types of carbonate cements in the study area.First and second types have no relationship to hydrocarbon;third type is partly related to hydrocarbon fluids;fourth type is diagenetic products of hydrocarbon fluids.The hydrocarbon fluid from Es₃x results in formation of carbonate cements,which are mainly calcites and iron calcites.For Es₄s,it results in formation of carbonate cements,which are mainly dolomite and ankerite.Along the pathways of hydrocarbon migration,there are variations in diagenesis products from feldspar dissolution and quartz overgrowth to authigenic kaolinites to carbonate cementation.