湖泊三角洲平原砂体的露头构形分析

本文应用等级界面与构形单元分析的方法，详细研究了鄂尔多斯盆地东北缘神木县考考乌素沟地区侏罗系延安组湖泊三角洲平原砂体的几何形态、空间配置和内部构形，并重点剖析了三角洲平原上的分流河道（含天然堤）和决口扇砂体，识别出５级界面体系，划分出１７种储层岩性相和４种构形单元。各级界面分别代表不同规模的非均质性，界面性质及伴生的渗透性隔挡层（泥质夹层）的分布控制了砂体的垂向和侧向连通性。储层岩性相是一种物质－能量单元，它们在砂体内的分布有一定规律。构形单元则是一种三维岩石单元，由第３至５级界面限定，具有各自特征的储层岩性相组合。界面和储层岩性相都是沉积水动力条件的综合反映，它们的不同组合反映了砂体内部非均质性的细微变化，并控制砂体的物性特征。物性在砂体内的分布按构形单元自然分区，高孔渗带主要分布在３至５级界面之上，多个构形单元和界面在垂向或侧向。的叠置，导致物性出现多阶正韵律的变化。代表水动力条件较强的储层岩性相，其物性较好，反之则差。

OUTCROP ANALYSIS OF ARCHITECTURE OF LACUSTRINE DELTAIC PLAIN SAND BODIES

With the aid of the method of bounding-surface hierarchy and architectural elements analysis,this paper discusses the geometry,spatial arrangement and internal architecture of lacustrine deltaic plain sand bodies in the Jurassic Yan'an Formation in Kaokaowusu Valley,Shenmu County on the northeast margin of the Ordos Basin.Furthermore,the distributary channel (including its natural levee)and crevasse splay sand bodies in the delta plain have been studied in detail,five orders of bounding surfaces have been recognized,and seventeen types of reservoir lithofacies and four types of architectural elements have been divided for these sand bodies.Each order of bounding surfaces represents different scales of heterogeneities. The character of bounding surfaces and the distribution of the permeability barrier(muddy.intercalation)associated with the third-order surface have controlled the vertical and lateral connection within sand bodies. The reservoir lithofacies with a regular distribution within sand bodies can be regarded as a kind of substance-energe units.The four architectural elements recognized in these sand bodies are channel(CH),sandy bed form(SB),lateral accretion(LA)and overbank fines (OF),which are bounded by the third-to fifth-order surfaces,and each has its characteristic assemblage of reservoir lithofacies.Bounding surfaces and reservoir lithofacies both are the synthetical reflection of sedimentary hydrodynamic conditions,and their various assemblages reflect the subtle variation of heterogeneity,and control the property of porosity and permeability within sand bodies.The distribution of porosity and permeability within sand bodies is'naturally divided into several districts according to architectural elements; the higher zones of porosity and permeability are mostly distributed on third-to fifth-order surfaces.The vertical and lateral overlapping of architectural elements and bounding surfaces results in the positiverhythmic variations in porosity and permeability.The porosity and permeability of the reservoir lithofacies representing stronger hydrodynamic conditions are much better than those of the lithofacies representing weaker hydrodynamic conditions.