准噶尔盆地西北缘三叠系干旱型冲积扇储层内部构型特征

Internal Architecture Characteristics of Triassic Arid Alluvial Fan in Northwestern Margin of Junggar Basin

以克拉玛依油田一中区为例,综合现代沉积、岩芯、露头、密井网等资料,应用层次分析法深入解剖干旱型冲积扇内部构型。以冲积扇相带划分为基础,构建7~9级构型要素分级体系,明确构型要素的成因、规模及样式,建立精细的干旱型冲积扇构型模式。研究表明:①根据岩性组合、沉积构造等特征将冲积扇依次划分为槽流、片流、辫流及径流4个相带;②槽流带主体为宽带状槽流沉积体,由多期槽流砾石体垂向叠置而成,单期槽流砾石体顶部在间洪期受到小股牵引流侵蚀改造,发育网状的流沟系统;③片流带主体为扇状片流砂砾体,由多期片流朵体侧向—垂向复合而成,朵体顶部披覆的泥质夹层是稳定的渗流屏障;④辫流带主体为宽带状辫流水道,由洪水水道和间洪水道两种单一水道侧向复合而成,洪水水道规模较大、侧向迁移频繁、切割叠置关系复杂、物性较好,在油田注水开发过程中极易形成水窜通道,而间洪水道规模较小,侧向切叠程度较低、物性也较差;⑤径流带主体为漫流细粒沉积,在漫流细粒沉积的背景上发育径流水道,其水道规模小、物性差且易尖灭。

Taking the Yizhong area of Karamay Oilfield as an example, fine reservoir architecture analysis using hierarchical analysis method based on comprehensive application of well logs, core data, outcrop and modern deposition data have been performed. Based on facies belt division, the grading system of seven to nine level reservoir architectural elements have been constructed. Then the formation causes, scale and distribution patterns of reservoir architectural elements have been explored, and finally the reservoir architecture model was constructed. The results show five aspects of cognition. Firstly, an alluvial fan can be divided into four facies belts, including trench flow belt, sheet flooding belt, braided stream channel belt and run-off belt. Secondly, the main subject of trench flow belt was broadband-like trench flow sediment bodies which vertically compounded by several trench flow gravel bodies. In inter-flood period, small scale streams erode the upper part of each trench flow gravel body, and a gully network formed. Thirdly, the main subject of sheet flooding belt was fan-like gravel-sand bodies which were laterally or vertically composed by several sheet flooding lobes. Muddy inter-layers covered at the top of lobes can be regarded as stable seepage barrier. Fourthly, the main subject of braided stream channel belt was braided channel association which was composed by several individual channels laterally （include flooding channel and inter-flood period channel）. Among these channels, flooding channels were easier to be flooded due to a larger scale, a higher degree of lateral complexity and better physical properties. On the contrary, inter-flood period channels have lower degree of lateral complexity and poor physical property. Fifthly, the main subject of run-off belt was overbank fine sediments. Run-off channels had small scale, poor physical properties and can pinch out easily at the head of distal fan.