坳陷湖盆大型浅水三角洲沉积特征与生长模式

坳陷湖盆大型浅水三角洲是目前中国陆上岩性油气藏规模储量增长的主体。通过对松辽盆地南部上白垩统保乾三角洲和现代鄱阳湖赣江三角洲解剖,重点探讨湖盆浅水三角洲形成的地质背景、沉积特征与生长模式。结果表面:①坳陷湖盆具有形成大型浅水三角洲的沉积背景,敞流型湖盆导致的湖平面频繁升降控制了浅水三角洲的纵横向发育规模。②松辽盆地南部上白垩统发育2种不同类型的三角洲,深湖型三角洲一般呈朵叶状,沉积亚相展布清晰,沉积微相以分流河道、河口坝和分流河道间为主;浅湖型三角洲一般呈鸟足状或树枝状,沉积亚相分异不明显,沉积微相以分流河道和分流河道间为主,河口坝不发育;③通过现代沉积遥感定量分析,刻画了鄱阳湖赣江中支三角洲近50年的发育特征和演化规律,揭示了分流河道从分散树枝状到闭合结网状的生长过程。④坳陷湖盆大型浅水三角洲是不断发育的多期朵叶体在平面上拼接而成的复合体,其中分流河道是最重要的储集砂体类型,在平面上呈结网状分布,控制了大面积岩性油气藏的分布与富集。

Depositional features and growth pattern of large shallow-water deltas in depression basin

Large shallow-water deltas in depression basin contribute to the main potential increase of onshore lithologic reservoirs in China.The Baoqian delta of the Upper Cretaceous in southern Songliao Basin and the modern Ganjiang delta in Poyang Lake were analyzed.The particular focus was put on the paleo-environment,depositional features and growth pattern of this type of delta.(1)Depression basins are favorable for large shallowwater deltas.Unconfined morphology results in the frequent rise and fall of lake-level,which controls the delta dimension in dip direction.(2)There are two different types of deltas in the Upper Cretaceous of southern Songliao Basin.One is deep-water delta characterized by lobe shape and easily-identified depositional facies,mainly including distributary channels,mouth bars,and interdistributary bays.Another is shallow-water delta characterized by bird's foot shape and obscure boundaries between depositional facies,mainly including distributary channels and interdistributary bays,with mouth bar less developed.(3)The remote sensing for modern sedimentary systems reveals the evolution of Ganjiang middle delta in Poyang Lake in recent 50 years,showing the transition from disperse branch shape to connective network shape.(4)Large shallow-water delta in depression basins is a complex consisting of several deltas formed in multi-scenarios.The sand-bodies of distributary channels are the most significant reservoir and carry massive lithologic reservoirs.They are distributed horizontally in a net pattern and control the distribution of lithologic reservoirs.