| Bayindulan is an oil-rich depression in Erlian Basin,which has been proved by exploration.Although a lot of researches have been done in the study area,there is not enough knowledge about the hydrocarbon generation capacity of source rocks,the geochemical properties of crude oil and the characteristics of hydrocarbon accumulation in the study area.Therefore,by combining geochemical data with petroleum geological data and using advanced experimental techniques,this paper systematically studies the geochemical characteristics of hydrocarbon source rocks,crude oil characteristics,oil and gas migration,and reservoir forming stages in Bayindulan depression.The results show that the Arshan formation and Tengger formation are the main source rocks in Bayindulan area.The source rocks of the Arshan formation have high organic matter abundance,good organic matter type and great hydrocarbon generating potential,and they are deposited in the environment of brackish water and salt water,which are the main source rocks in the study area.The source rocks of the tenger formation mainly contribute to the first tenger formation,and the organic matter abundance,type and maturity of the first tenger formation are high It belongs to low maturity,mainly in brackish water sedimentary environment,and its hydrocarbon generating potential is weaker than that of the source rock of ALSHAN formation;in addition,there are over mature source rocks in Jurassic system.According to the analysis of the thermal evolution history,the threshold of hydrocarbon generation is low,which is affected by the salt water environment and has the characteristics of early hydrocarbon generation.In general,the crude oil in the South Bayindulan depression has the characteristics of high density,high viscosity,high wax content,high non hydrocarbon and asphaltene content.The heavy oil is widely distributed,and the density and viscosity decrease with the increase of burial depth.The north depression is mainly normal crude oil.According to the characteristics of normal alkanes,isoprene like alkanes,steranes and terpanes in crude oil,the crude oil in the study area is divided into four types: low mature crude oil,low mature crude oil,mature crude oil and biodegradation crude oil.The biodegradation is in the middle degree,and the source material type is mainly higher plants,with the contribution of aquatic organisms.In addition,the heavy oil in the study area is mainly divided into primary heavy oil and biodegradable heavy oil.Based on the index of crude oil salinization in Erlian Basin,the characteristics of crude oil salinization in the study area are analyzed from organic and inorganic geochemical aspects.The reservoir types in the study area are mainly lithologic reservoir and structural lithologic reservoir,which are generally weakly affected by structural action.Through oil source correlation,it is pointed out that the crude oil in the study area are all of the same origin,all of them come from the source rock of ALSHAN formation,and there is the characteristics of near source reservoir formation.Only the primary migration or very short secondary migration of oil and gas occurs through sand body and fault dredging,and they gather in the nearby reservoir to form the oil and gas reservoir in the source.Based on the analysis of the burial history and inclusion characteristics of the study area,it is pointed out that the reservoir in Bayindulan sag is mainly controlled by structural inversion,and there are two hydrocarbon generation periods in the evolution process of source rock,i.e.the end of teng-1-the beginning of Teng-2 and the end of Saihan,when the depression reverses and uplifts in the end of Teng-2,the buried depth of source rock becomes shallow and the temperature decreases,and then it is deposited in Saihan,with the buried depth increasing The contribution of the two hydrocarbon generation is different because of the difference of sedimentary rate in the same structural location. |
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