川东建南地区须家河组储层特征及发育控制因素研究

Reservoir Characteristics and Main Controlling Factors of the Xujiahe Formation in the Jiannan Area,Eastern Sichuan Basin

川东建南地区须家河组砂岩致密化程度高,非均质性强,有利储层的发育分布成为勘探的难点。本文基于铸体薄片、扫描电镜和实测物性等分析化验资料,在查明须家河组砂岩的岩石学特征、物性特征和孔隙结构特征的基础上,揭示砂岩的致密化成因和储层发育控制因素。建南地区须家河组砂岩中塑性岩屑含量较高,岩石类型以岩屑砂岩为主,含有少量岩屑石英砂岩、长石岩屑砂岩和岩屑长石砂岩;砂岩的储集物性较差,以超低孔、超低渗储层为主,孔隙度均值3.9%,渗透率均值0.46 mD,孔隙度大于5%的相对优质储层主要分布在须四段砂岩中。砂岩致密化程度高与早成岩期强烈的压实作用和中成岩期进一步的钙质、硅质胶结作用有关,但其根本原因是受砂岩原始物质组构的控制,较高的塑性岩屑含量是导致研究区砂岩压实作用强烈,物性较差的重要原因;仅在塑性岩屑含量较低且长石含量较高的砂岩中发育优质储层。

The sandstone of the Xujiahe Formation in Jiannan area of eastern Sichuan Province has high degree of densification and strong heterogeneity,so the development and distribution of its favorable reservoirs become the difficulty of exploration.Based on the analysis and test data of cast thin section,scanning electron microscope and measured physical properties,this paper finds out the petrology,physical properties and pore structure characteristics of sandstone in the Xujiahe Formation,reveals the origin of sandstone densification and the controlling factors of reservoir development.The sandstone has a high content of plastic cuttings,and its rock type is mainly lithic sandstone,with minor lithic quartz sandstone,feldspar lithic sandstone and lithic arkose.The reservoir physical property of sandstone is poor,mainly with ultra-low porosity(average porosity of 3.9%)and ultra-low permeability(average permeability of 0.46%).The relatively high quality reservoirs with porosity more than 5%are mainly distributed in the fourth member of the Xujiahe formation.The high densification of sandstone is controlled by its original material fabric besides the strong compaction in the early diagenetic stage and the further calcareous and siliceous cementation in the middle diagenetic stage.The high content of plastic cuttings is an important reason for the strong compaction and poor physical properties of sandstone in the study area;only in the sandstone with low content of plastic cuttings and high content of feldspar high quality reservoir is developed.