塔里木盆地轮南—古城地区寒武系大型台地边缘层序结构、沉积演化及油气勘探潜力

Sequence architecture,sedimentary evolution and hydrocarbon exploration potential of the large Cambrian platform margin in Lunnan-Gucheng area of Tarim Basin

针对塔里木盆地轮南—古城地区寒武系台缘带规模储-盖组合的类型及时空分布不清的问题,利用最新采集/拼接处理的轮南—富满地区的三维地震数据体、30余条二维地震格架测线、9口钻井的岩屑薄片和碳/氧稳定同位素曲线等资料,建立了台地内部—台地边缘—盆地的年代地层格架,开展了以层序或体系域为单元的沉积相研究,落实了规模储-盖组合和烃源岩分布特征,评价了有利勘探区带。研究结果表明:①寒武系台缘带可识别出4个二级层序和11个三级层序,横向上,层序结构差异明显,轮南地区结构完整,具典型侧向叠置的特征,而古城地区部分缺失纽芬兰统—第二统(SQ1—SQ3)层序且垂向加积"堆垛"特点突出;②时间上,轮南—古城地区依次经历了富泥质缓坡、低角度前积缓坡—弱镶边台地、垂向加积蒸发潟湖占主导镶边台地和侧向加积平顶镶边台地4个演化阶段,塔南古陆和古海平面等控制了空间差异;③轮南—古城地区发育9套台缘丘滩带(SQ3—SQ11)、3套膏盐岩(SQ5—SQ7)以及陆棚相和斜坡相两类烃源岩(SQ1、SQ6、SQ8—SQ11);④评价出膏下台缘丘滩带、泥下残余丘滩带、致密碳酸盐岩下丘滩带和泥间斜坡重力流4类有效储-盖组合,构建了5类成藏模式,膏下台缘丘滩带和泥下残余丘滩带是近期实现勘探突破并实施万米深地钻探的最佳储-盖组合,泥间斜坡重力流也是一种值得探索的新类型储-盖组合。

In response to the unclear types and temporal-spatial distribution of the large-scale reservoir-cap assemblages of Cambrian platform margin in Lunnan-Gucheng area of Tarim Basin,based on the latest collected/merged three-dimensional seismic data,more than 30 two-dimensional seismic survey lines,thin sections of rock debris from 9 drilling wells,and C/O stable isotope curves from the Lunnan-Fuman area,the paper establishes a chronostratigraphic framework from platform interior to platform margin to basin,carries out the research of sedimentary facies using the sequence or system tract as a unit,makes clear large-scale reservoir-cap assemblages and source rock distribution,and evaluates favorable exploration zones.The research results show as follows.(1)Four second-order sequences and 11 third-order sequences are identified in Cambrian platform margin.Horizontally,there are significant differences in sequence architecture.The Lunnan area features a complete structure with typical lateral stacking,while Gucheng area partially lacks sequences from Terreneuvian to Epoch2(SQ1-SQ3)and has the prominent characteristic of vertical accretion and stacking.(2)Lunnan-Gucheng area experienced four evolution stages in succession,i.e.,mud-rich ramp,low-angle progradation ramp to weak-rimmed platform,rimmed platform dominated by vertical accretion evaporation lagoon,and lateral accretion flat-topped rimmed platform,and the spatial differentiation was controlled by Tanan oldland and ancient sea level.(3)Nine sets of platform margin mound-shoal belts(SQ3-SQ11),3 sets of gypsum salt rock belts(SQ5-SQ7),and 6 sets of source rocks(SQ1,SQ6,SQ8-SQ11)have been developed in Lunnan-Gucheng area.(4)Four types of effective reservoir-cap assemblages,i.e.,the platform margin mound-shoal belt covered with gypsum,the residue mound-shoal belt covered with soil,the mound-shoal belt covered with compact carbonate rocks,and the slope gravity flow,were evaluated and five types of hydrocarbon accumulation models were established.The platform margin mound-shoal belt covered with gypsum and the residue mound-shoal belt covered with soil are the best reservoir-cap assemblage,where recent breakthroughs have been made and the depth of drilling can reach 10000 m.The gravity flow on mud slopes is also a new type of reservoir-cap assemblage worthy of exploring.