浅水三角洲物源、砂体构型与储层特征研究——以准噶尔盆地永进—莫西庄地区侏罗系三工河组二段为例

针对准噶尔盆地腹部侏罗系三工河组物源、砂体构型及储层物性认识存在争议的问题,笔者等基于岩芯、录井、钻井等方面的资料,结合前人在准噶尔盆地周缘磷灰石及锆石年龄数据,运用沉积学、层序地层学、沉积盆地分析及储层沉积学的基本原理和方法对三工河组二段物源方向、远近和类型、沉积体系展布、砂体构型及储层物性之间的关系进行了系统的研究。研究表明,在敞流盆地快速抬升/缓慢沉降的构造背景下形成辫状河三角洲退积式沉积序列,在五级层序地层格架中,河道强冲刷叠置砂体见于第1、2砂组,三角洲退积,分支河道强烈冲刷,导致河道砂体叠置,微相类型单一,单砂体厚度向上变薄,砂体全区稳定分布,储集性较好。河道弱冲刷叠置砂体见于第3、5砂组,三角洲退积,分支河道冲刷不明显,形成河道“二元结构”,单砂体厚度向上变薄,粒度变细,储集性好;河口坝组合砂体见于第4砂组,在三角洲退积过程中,水下分流河道末端形成河口坝,总体岩性向上变细,砂体不连续,储集性好,远砂坝席状砂组合砂体见于第6、7砂组,砂体零星分布,储集性很差。在浅水、低可容纳空间、快速抬升/缓慢幕式沉降构造背景之下,浅水三角洲的物源的方向、远近及类型是影响沉积微相展布的关键因素,也是影响砂体构型及其储层物性的物质基础。

Study on shallow water delta provenance, sandbody architecture and reservoir characteristics——A case of the 2nd Member of the Jurassic Sangonghe Formation in Yongjin—Moxizhuang region, Junggar basin

Based on the data from cores, logs, and drilling, and combined with previous data on apatite and zircon ages at the periphery of the Junggar Basin, this paper presents a systematic study of the relationship between the provenance directions, provenance types, sedimentary system spreading, sand configuration, and reservoir properties of the 2nd member of Jurassic Sangonghe Formation based on the basic principles and methods of sedimentology, stratigraphic stratigraphy, sedimentary basin analysis, and reservoir sedimentology, The study shows that the braided river regressive sedimentary sequence was formed under the tectonic background of rapid uplift/slow subsidence, and in the five- level stratigraphic framework, the strongly scoured superimposed sand bodies of the river channel are found in the 1st and 2nd sandbody assemblages, with delta regression and strong scouring of branch channels, resulting in superimposed sand bodies of the river channel, with a single microfacies type, single sand body thickness thinning upward, stable distribution of sand bodies in the whole area, and good reservoir properties. Weakly scoured superimposed sand bodies are found in the 3rd and 5th sandbody assemblage where the delta is receding and the branch channels are not obviously scoured, forming a "binary structure" of the river, with single sand body thickness thinning upward, fine grain size and good reservoir properties; the combined sand body of the river dam is found in the 4th sandbody assemblage, where a mouth bar is formed at the end of the submerged diversion channel in the process of delta receding. In conclusion, under the background of shallow water, low accommodation space, rapid uplift- slow curtain settlement tectonics, the direction, proximity and type of the source of shallow water delta are the key factors affecting the distribution of sedimentary micro- phase, and also affecting the sand body configuration and its reservoir properties and material basis.