鄂尔多斯盆地苏里格气田苏6区块二叠系下石盒子组8段砂岩储层致密成因模式

利用岩石薄片、扫描电镜、电子探针、能谱分析、包裹体测温及拉曼光谱分析等分析方法,对鄂尔多斯盆地苏里格气田苏6区块二叠系下石盒子组8段储层的致密化模式进行研究。结果表明,(1)储层的致密化过程主要为前期压实和Ⅰ期硅质胶结→Ⅱ期硅质胶结和绿泥石包膜→Ⅰ期溶蚀(天然气充注)→后期压实和Ⅲ期硅质胶结(储层致密化)→Ⅱ期溶蚀和Ⅳ期硅质胶结→绿泥石胶结和交代→碳酸盐胶结和交代。(2)储层的致密化模式有三种类型,中粗粒岩屑砂岩为强机械压实致密化模式,中粗粒岩屑石英砂岩为强硅质胶结、较强机械压实致密化模式,细粒(长石)岩屑砂岩为强压实、较强硅质胶结致密化模式。(3)机械压实作用和硅质胶结作用是储层致密化的主要原因;致密化后封闭条件下成岩流体的Ⅱ期溶蚀作用较弱,也是储层现今保持致密化的重要原因。(4)两类中粗粒砂岩在天然气主要充注时期之后达到致密,有机酸的注入导致溶蚀孔隙相对较发育,细粒(长石)岩屑砂岩在有机酸充注之前已经致密,溶蚀作用较弱。(5)储层致密化过程的差异,导致了中粗粒砂岩孔隙度、渗透率的大小以及渗透率—孔隙度的相关程度明显高于细粒砂岩。

Densification Modes of Sandstone Reservoir in the 8th Member of the Lower Shihezi Formation, Permian, in Su 6 Area of Sulige Gas Field,Ordos Basin

Densification modes of tight sandstone reservoir of the 8th Member of Lower Shihezi Formation,Permian,in Su-6 Area of the Sulige Gas Field, Ordos Basin, are quantitatively analysised by means of slice identification, scan electron microscope,electron probe micro-analysis and energy spectrum,homogenization temperatures and raman microprobe research of fluid inclusions. The results are as follows: (1) Densification process can be divided into the following stages, compaction during early diagenesis and the 1st stage siliceous cementationthe 2nd stage siliceous cementation and grain-coating chloritethe 1st stage dissolution(hydrocarbon charge)compaction during late diagenesis and the 3rd stage siliceous cementation (densification of reservoir) the 2nd stage dissolution and the 4th stage siliceous cementationcementation and replacement of chloritecementation and replacement of carbonate. (2) Densification modes of reservoir can be divided into three types: densification of medium-coarse grained litharenite by strong compaction; densification of medium-coarse grained lithic quartzarenite by strong siliceous cementation and medium to strong compaction; densification of fine grained (feldspathic) litharenite by strong compaction and medium to strong siliceous cementation. (3) The main reasons for densification of reservoir are compaction and siliceous cementation. And the 2nd stage dissolution under enclosed environment has less ascension of porosity, which is another important reason for densification. (4) The two types of medium-coarse grained sandstones are densification after hydrocarbon charge, which experience injection of organic acid and make dissolved pore to be the major storage space. Fine grained (feldspathic) litharenite is densification before hydrocarbon charge,which experience weak dissolution. (5) Difference of densification modes lead to the porosity,permeability ,correlation of permeability and porosity of medium-coarse grained sandstone are significantly higher than that of fine grained sandstone.