四川盆地奥陶系五峰组–志留系龙马溪组黄铁矿–有机聚合体特征

Characteristics of pyrite and organic matter aggregates in the Ordovician Wufeng-Silurian Longmaxi Formation,Sichuan Basin

四川盆地奥陶系五峰组–志留系龙马溪组黄铁矿–有机聚合体(FPA-OMA)丰富,通过扫描电镜结合氩离子抛光技术观察FPA-OMA赋存特征并探讨其形成机制及油气地质意义。结果表明, FPA-OMA可以划分为2类4亚类,Ⅰ_(1)亚类和Ⅱ_1亚类FPA-OMA富有机孔,Ⅰ_(2)亚类和Ⅱ_2亚类FPA-OMA缺乏有机孔。OMA由疏松多孔的沉积有机质聚合体转化形成,FPA为深水陆棚环境水–沉积物界面生物诱导形成的自生矿物聚合体,二者形成时序为OMA→FPA。FPA-OMA类型由OMA疏松程度决定,孔隙稀疏的OMA有利于形成Ⅰ类FPA-OMA,孔隙密集的OMA有利于形成Ⅱ类FPA-OMA。FPA-OMA有机孔发育程度与围岩抗压实强度有关,刚性颗粒作骨架的页岩抵抗压实作用能力强而发育有机孔,塑性颗粒承担巨大上覆地层压力的页岩难以保存有机孔, FPA并不能保护有机孔。

There are abundant framboidal pyrite and organic matter aggregates(FPA-OMA)in the shale reservoirs throughout the Wufeng-Longmaxi Formation in the Sichuan Basin,Southwest China.Occurrence of the FPA-OMA were by using scanning electron microscopy combined with argon-ion polishing shale technology,and their formation mechanism and geological significance were further discussed here.The FPA-OMA is divided into 2 categories and 4 subclasses.The SubclassⅠ_(1) andⅡ_(1) FPA-OMA have rich organic matter pores,whereas the SubclassⅠ_(2) andⅡ_(2) FPA-OMA have no organic matter pores.OMA is potentially transformed from loose and porous sedimentary organic matter aggregation,whereas FPA is authigenic mineral aggregation formed by biological induction at the water-sediment interface in deep water shelf environments.Their formation sequence is OMA→FPA.The type of FPA-OMA is determined by the pore density in the OMA.OMA with sparse pores is conducive to the formation of the ClassⅠFPA-OMA.OMAs with more pores promoted the formation of the ClassⅡFPA-OMA.The development of organic matter pores in the FPA-OMA is related to the compaction strength of the surrounding rocks.The shale reservoir with rigid particles as its skeleton has a strong ability to resist compaction and develop organic pores.The shale containing plastic particles bearing high upward pressure is difficult to preserve pores due to the tighter compaction of organic matter because FPA does not protect organic pores effectively.