合川地区须二段砂岩储层成岩作用及其对储层的影响

依据普通薄片、铸体薄片、扫描电镜、X衍射等实验分析手段,对合川地区须家河组二段砂岩储层的岩石学特征、成岩作用及孔隙演化进行了研究。结果表明,该区须二段砂岩储层主要由长石岩屑砂岩和岩屑长石砂岩组成。主要成岩作用类型有压实作用、胶结作用、溶蚀作用和交代作用,成岩演化阶段已达到中成岩B期。早成岩A期—B期,压实作用强烈,原生孔隙迅速减少;中成岩A期,压实作用及硅质胶结作用是原生孔隙继续降低,有机质热演化过程中产生的有机酸及无机酸,使长石及富长石的岩屑颗粒发生强烈溶蚀,形成大量次生孔隙;中成岩B期,含铁方解石及铁白云石交代充填,使储层致密。压实作用及胶结作用是原生孔隙遭受破坏的主要成岩作用类型,而溶蚀作用是形成次生孔隙的主要成岩作用类型。受成岩作用及成岩演化阶段的控制,研究区须二段储集空间类型多样,粒内溶孔、粒间溶孔及残余粒间孔发育,特别是长石及富长石岩屑颗粒的溶蚀,使须二段储层出现孔隙度、渗透率异常发育带。

The diagenesis of the 2nd Member reservoirs of Xujiahe Formation and its influence on reservoirs of Hechuan area

Using the analytical means such as ordinary thin slice,cast thin slice,scanning electron microscope and X-diffraction,the authors conducted researches on the characteristics of petrology,diagenesis and pore evolution of the 2nd Member sandstone reservoirs of Xujiahe Formation in Hechuan area,and the result indicates that the sandstone reservoirs are mainly composed of feldspar lithic sandstone and lithic sandstone,which have mainly experienced compaction,cementation,dissolution and metasomatism,with the diagenetic phase reaching the middle diagenetic stage B.Primary pores decreased rapidly due to strong compaction during the early diagenentic stage A～B,and primary pores were reduced continuously due to the compaction and siliceous cementation,together with the increase of induced pores resulting from the dissolution of feldspars and the cutting of grains rich in feldspar during the middle diagenetic stage A.In addition,the metasomatism-filling of iron-bearing calcite and ankerite caused the tightness of the reservoir during the middle diagenetic stage B.The compaction and cementation seem to be the main diagenetic types which destroyed the primary pores.The dissolution was the main diagenetic action to form the induced pores.Controlled by diagenesis and diagenetic phase,there exist many types of reservoir space in the 2nd Member of Xujiahe Formation in Hechuan area: intragranular dissolving pores,intergranular dissolving pores and remnant intergranular pores are well developed,and the induced pores growing belt abnormally appears in the 2nd Member of Xujiahe Formation in Hechuan area,resulting from the corrosion of feldspars and the cutting of grains rich in feldspar.