鄂尔多斯盆地下石盒子组盒8段储集砂体发育控制因素及沉积模式研究

Research on development factors and the deposition Model of large area reservoir sandstones of He8 section of Xiashihezi Formation of Permian in Ordos basin

以鄂尔多斯盆地二叠系下石盒子组盒8段储集砂体为研究对象,在众多前人研究成果的基础上,综合研究了盆地内下石盒子组盒8段沉积演化过程中储集砂体发育特征,主要表现为:岩石类型多样,包括含砾粗砂岩、中粒砂岩、细粒砂岩等;成因复杂:包括冲积扇砂体、河流砂体、辫状河三角洲砂体等;分布广泛:具有广覆式大面积分布特征。在上述基础上,系统深入分析了控制盒8大面积砂体分布的关键因素,主要包括:强物源、多物源供给是基础,多水系发育是前提,平缓古地貌是背景,高流速河流是动力。其中,强物源、多物源不仅为盆地内提供了丰富碎屑物质,而且控制着盆地内不同区域储集砂体的岩性特征;多水系发育为形成大面积砂体分布提供了条件,发源于物源区向盆地内搬运陆源碎屑物质的六条水浅流急的辫状河道在盆地中部汇合交叉控制着单层砂体厚度及其连片性。平缓古地貌控制着多河道发育和长距离搬运过程中河道摆动、迁移频繁,并相互叠置交叉。高流速河流控制着平缓古地形上发育的多河道不断交叉、复合。并定量计算了盒8段储集砂体沉积时的地形古坡度,平均坡降为1.10m.km-1,平均坡度为0.063°;古河流水体平均流速为8.31m.s-1。进而,结合盆地内钻井实际建立了下石盒子组盒8段独具特色的"强物源供给的缓坡浅水辫状河三角洲沉积模式"。

This paper taking reservoir sandbodies of He8 section of Xiashihezi Formation of Permian in Ordos basin as the research object.Based on many previous studies,the ＂large area wide distribution＂ features of reservoir sandbodies of He8 section comprehensive studied and the key factors of control large area distribution of reservoir sandbodies of He8 analyzed systematically in detail which included：strong source supply is based,multi-water development is the prerequisite,gentle landscape is the background,high velocity stream is the driving force.And the ancient terrain slope and water flow rate are quantitative calculated,the average gradient is 1.10m·km-1,average slope is 0.063°;the average water flow rate is 8.31m·s-1.Then,the ＂braided river delta of strong source supply and shallow-water slope＂ unique depositional model of He8 section is created.