扇三角洲高分辨率层序构型及砂体预测——以沙湾凹陷西斜坡二叠系上乌尔禾组为例

High-resolution Sequence Architecture and Sandbody Distribution Prediction of Fan Delta:A Case Study of Upper Wuerhe Formation of Permian in West Slope of Shawan Sag

准噶尔盆地西北缘沙湾凹陷西斜坡二叠系上乌尔禾组已有的层序和沉积相研究较粗,砂体预测缺乏定量表征,为了明确砂体发育特征及其展布规律,结合区域地质背景,综合地震、测井、录井等资料,建立了高分辨层序构型。通过分析超短期旋回层序内的缓坡浅水扇三角洲水下分流河道单井相,建立了单一型、水道天然堤复合型、侧向迁移型、非限制型、半限制型和限制型复合水道6种地质模式。结合地震正演,构建了研究区地震振幅、水道砂体厚度及水道宽度的定量关系。结果表明,缓慢退积型低位旋回层序内水下分流河道砂体是优质储层发育的主要位置。随着远离物源,垂向叠置横向连片的水道砂体逐渐呈现条带状分布;快速退积型湖侵旋回层序底部水下分流河道砂体部分发育,整体呈孤立状条带展布。

The existing studies on sequence and sedimentary facies of upper Wuerhe formation of Permian in the west slope of Shawan sag,northwest margin of Junggar Basin are not detailed enough,and the prediction of sand bodies lacks quantitative characterization.In order to make clear the development characteristics and distribution law of sand bodies,the high-resolution sequence architecture is established according to regional geological background and seismic,logging,mud logging data.The geological models of six types of composite channels are established by analyzing single well facies of fan delta underwater distributary channel in ultra short-term cycle sequence,including single channel,channel-natural dike composite channel,lateral migration composite channel,unrestricted composite channel,semi-restricted composite channel and restricted composite channel.Combined with seismic forward modeling,the quantitative relationship among seismic amplitude,channel sand body thickness and channel width is constructed.The results show that the subaqueous distributary channel sandbodies are the main position of high-quality reservoir development in the low-level cycle sequence of slow retrogradation type.With the increase of the distance from the source,the vertically superimposed and horizontally contiguous channel sandbodies gradually present a banded distribution;the subaqueous distributary channel sandbodies at the bottom of fast retrogradation lake transgression cycle sequence are partially developed,and the overall distribution is isolated strip.