川西丰谷构造须家河组四段钙屑砂岩优质储层控制因素

Controlling Factors for T_3x_4 Calcarenaceous Sandstone in Fenggu Structure,Western Sichuan Basin

钙屑砂岩在整个川西坳陷须家河组四段广泛发育,且普遍致密。采用铸体薄片、扫描电镜、物性分析和水岩实验等手段,对丰谷构造须四段钙屑砂岩的基本特征进行了分析,探讨了沉积环境、成岩作用和构造运动对该类型优质储层形成的控制作用。结果表明,研究区钙屑砂岩分选中等—好,成分成熟度低,主要的储集空间为粒间溶孔和残余粒间孔,属特低孔特低渗储层。沉积作用和成岩作用是钙屑砂岩优质储层形成的主控因素。其中,发育在高能相带、且碳酸盐岩岩屑含量高(>90%)是钙屑砂岩优质储层发育的先决条件;而埋藏成岩过程中有机酸的溶蚀、烃类的早期充注和早期方解石胶结物的少量生成是钙屑砂岩优质储层孔隙保存及次生溶孔形成的关键。

Upper Triassic Xujiahe calcarenaceous sandstone is widespread and tight in the west Sichuan depression. The high-quality reservoir of calcarenaceous sandstone was firstly touched in the Fenggu struc ture in 2005. It is change the view that calcarenaceous sandstone can not form reservoir. So far,the controlling factors for the formation of high quality reservoir of calcarenaceous sandstone are unclear. In this paper, we use cast thin-sections, scanning electron microscope, physical analysis, and water-rock interaction to describe the basic characteristics of T3x4 calcarenaceous sandstone in the Fenggu structure. We discuss the potential reasons including sedimentary environment,diagenesis and tectonic movement to control the formation reasons of high-quality reservoir of calcarenaceous sandstone. The results show that the calcarenaceous sandstone is characterized by medium-well sort, low compositional maturity and medium-fine grained. The reservoir space bears dissolved pores between grains and residual intergranular pores, belonging to extra low porosity and extra-low permeability reservoir. Sedimentary and diagenesis are major factors for the formation of high-quality reservoir of calcarenaceous sandstone. Among them, the favorable sedimentary facies zone and high ealcarenaceous content are the preconditions to form high-quality reservoir. The dissolution of organic acids, filling of early hydrocarbons and cementation of early carbonates under the buried process are the keys to form high-quality reservoir.