四川盆地龙马溪组页岩气储层石英类型与特征

为了解页岩气储层石英类型和特征,以四川盆地龙马溪组页岩为研究对象,对样品进行了薄片观察、氩离子抛光-场发射环境扫描电镜观察、能谱分析、X-射线衍射分析、有机碳含量测试。结果表明,龙马溪组页岩石英含量在23%~83%之间,平均值为52%。根据成因,可分为5类:陆源碎屑石英、生物骨骼相关石英、沉积期-成岩早期混合石英、成岩期自生石英和裂缝中石英脉。石英含量与有机碳含量成正相关,其中有机石英在还原环境下能更好地指示有机质的发育情况。有机石英是指保留有软体并演化成干酪根的生物骨骼石英、交代生物骨架石英和与沥青伴生石英。与沥青伴生石英堆积在页岩原生孔隙中,降低了储层的孔隙度,但在一定程度上抑制了后期成岩作用,为沥青的充注保留了空间,且石英与沥青之间发育的缝隙与有机孔一起形成连通的孔隙网络。

Types and characteristics of quartzs in shale gas reservoirs of the Longmaxi Formation,Sichuan Basin,China

In order to analyze types and characteristics of quartzs in shale gas reservoirs,the Longmaxi Formation shale in Sichuan Basin was taken as the main object of this study.The samples were observed by using thin section identification and scanning electron microscopy(SEM)of argon ion polishing-field emission environment,analyzed by using energy spectrum analysis and X-ray diffraction analysis,and analyzed for their organic carbon contents.The quartz contents of the Longmaxi Formation shale range from 23%to 83%with an average of 52%.The quartz can be classified into five types including the terrigenous clastic quartz,bio-skeletal related quartz,mixture of sedimentary and early diagenetic quartzs,diagenetically authigenic quartz,and quartz veins in fissures.Quartz contents are positively correlated with organic carbon contents.Especially,organic quartz can be used to betterly indicate the development of organic matter in the reduced environment.Organic quartz refers to the bio-skeletal quartz which retains kerogen evolved from soft matters,quartz for replacing bio-skeletons,and quartz associated with bitumen.The accumulation of bitumen-associated quartz in primary pores of the shale resulted in the reduction of the porosity of reservoir,but the inhibition of the late diagenesis to a certain extent,the reservation of pores for infilling bitumen,and the formation of a connected pore network by organic pores and gaps between quartz and bitumen.