Hydrocarbon Charging And Accumulation Mechanism Of Tight Oil

As a kind of important unconventional resources,tight oil has attracted much attention in recent years.The Ordos Basin is one of the most typical large and tight sandstone oil and gas areas in China,and it has achieved remarkable achievements in the exploration and development of ultra-low and ultra-low permeability in the Mesozoic group.However,the mechanism of tight oil charging and mechanism of accumulation is still not very clear,which restricts the exploration results.Based on the study on the structural environment,sedimentary background and reservoir characteristics,this paper carried out the study of tight oil charging process,and discussed the dynamic mechanism,transport mechanism and the main control factors of hydrocarbon accumulation in tight oil reservoirs,which could provide scientific basis for the further increase of production in the Ordos Basin and reveal the forming mechanism of "continuous accumulation and continuous distribution" of tight oil,supplemented and improved the geological theory of tight oil reservoir,and could guide the evaluation of resource evaluation,favorable area forecast and exploration deployment of tight oil.This paper has gained new insights in the following:The palaeophysical characteristics of the tight reservoir in various diagenetic stages were restored.Lengthened for oilfield in the western region dense group of braided river delta facies sandstone reservoir,a variety of analysis and test,the combination of research to extend the YanChang formation of the 6 and 7 group of dense oil reservoir characteristics,diagenetic evolution and pore structure,which reveals the reservoir experienced three diagenetic stages of change,achieve densification,precocious rock phase B reservoir compaction and cementation are the main reason for the reservoir density,and on the basis of the understanding,discussed the antiquities recovery method,calculated the antiquities of the diagenetic stage of reservoir.The relationship between reservoir densification and gas charging is discussed.By organic fluid reservoir features,the inclusion and burial history analysis,show that of ordos basin has experienced three periods of hydrocarbon charging,and reservoir diagenetic evolution and the hydrocarbon expulsion period of hydrocarbon source rock,the combination of that of ordos basin experienced a diagenesis,while density,hydrocarbon generation,while charging process,that is to say,dense oil reservoir charging and compacting simultaneously,is a continuous process of parallel for a long time the main reservoiring stage of the reservoir has densification.In this paper,the evolution of three stages of reservoir charging is proposed,namely,"buoyancy charging-fluid pressure difference-uplift negative pressure".By establishing the correlation relationship between the pressure and the permeability,the resistance of the tight oil charging in the Ordos Basin was restored,and the continuous oil column height required by the oil migration to overcome the resistance,and combined with the restoration of the ancient pressure characteristics of the reservoir,it was believed that the extension of the ordos basin would undergo three stages of evolution under the influence of diagenesis,hydrocarbon generation and tectonic movement.The oil charging pattern of the extended group in the Ordos Basin was established: the early crude oil was driven by the buoyancy in the middle and low permeability reservoirs,and the accumulation was carried out.In the formation process of dense reservoir,the original oil transportation accumulation and diagenesis are alternately carried out,and the fluid pressure difference driven by hydrocarbon generation is concentrated in the sand body near the source rocks.Under the condition of the late dense reservoir,the abnormal high pressure formed by hydrocarbon supercharging continues to promote the migration and accumulation of the oil and gas from the source rocks in the dense transmission layer of adjacent hydrocarbon source rocks.At the same time,the early accumulation of oil and gas is driven by the uplift negative pressure,and the long distance vertical and lateral migration adjustment are carried out along the microcrack and the dominant channel.During the diagenetic evolution,the dense reservoir underwent multiple hydrocarbon charging-continuous accumulation-late adjustment to form the present quasi-continuous tight reservoir.