摘要
依据地震、钻井、测井、地层对比以及地层厚度等资料,对松辽盆地古龙凹陷泉头组坡折带进行了深入研究,发现该区发育三种类型坡折,即断裂坡折、挠曲坡折和沉积坡折,坡折带沿着凹陷西部英台鼻状构造呈南北向弧形分布,平均坡降介于19‰~50‰之间。坡折带的发育对层序结构及沉积演化具有重要控制作用,断裂坡折带发育于层序的底部,控制了SQ1~1河流相加积型层序的发育,其特点是坡折下部地层厚度是上部的2倍。挠曲坡折带发育于层序中部,呈现缓坡带(α)和陡坡带(β)两段式特点,四级层序SQ2~1在坡折部位发育密集的上超点,形成了以湖相上超为特点的层序结构,同时坡折带两侧地层具有上薄下厚的分布格局。沉积坡折带分布在层序顶部,控制了五级层序SQ2~(2-1)的发育,形成了湖泊—三角洲相进积型层序,具有坡折下部薄、上部厚的分布特点。断裂坡折带控制的河流相加积型层序,有利于断层上倾遮挡及点坝透镜体圈闭的发育;挠曲坡折带控制的湖相上超型层序,有利于岩性上倾尖灭圈闭的发育;沉积坡折带控制的湖泊—三角洲进积型层序,有利于河口坝型岩性圈闭的发育,因此,坡折带的研究对于松辽盆地古龙凹陷油气勘探具有重要的指导意义。
Based on data analyses of seismic,well drilling,logging,and stratigraphic correlation and thickness,we conduct an in-depth investigation of the slope break belt in the Quantou Formation,Gulong sag,Songliao Basin.Results show that there are three types of belts in the study area,i.e.,fault slope-break belt,flexural slope-break belt and depositional slope-break belt.The slope-break belts distribute in a north-south arc pattern along the Yingtai nose-shape structure of the west of the Gulong sag.Average gradient of the belt ranges from 19‰ to 50‰.The development of the slope break belt controls the structures of sedimentary sequence and the sedimentary environment.The fault slope break belt develops at the bottom of the sequence,and controls the development of the SQ1~1 aggradation sequences of fluvial facies.It is characterized by that the thickness of the lower sequence is 2 times that of the upper sequence.The flexural slope-break belt develops in the middle of the sequence,and presents a two-section feature of the gentle slope belt(α)and the steep slope belt(β).The fourth order sequence SQ2~1 developed dense onlap points in the slope belt,forming a lacustrine onlap sequence structure.The thickness of the strata in the two sides of the slope belt is characterized by thinner upper part and thicker lower part.The depositional slope-break belt distributes on the top of the sequence,which controls the development of the fifth order sequence SQ2~(2-1),forming a progradation sequence of laucustrine delta facies.Its thickness is characterized by thinner lower part and thicker upper part.The fault slope-break belt controls the aggradation sequence of fluvial facies,which is beneficial for the development of traps with upward-dip sheltering by fault and point-bar lens.The flexural slope-break belt controls the lacustrine onlap sequence,which is beneficial for the development of lithologic traps that are characterized by the styles of updip wedge-out.The depositional slope-break belt controls the progradation sequence of lacustrine delta facies,which is beneficial for the development of the mouth bar lithologic traps.Therefore,the study of the slope-break belt is of significance to the oil and gas exploration in the Gulong sag of the Songliao Basin.
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