陆相细粒岩储层质量的控制因素——以四川盆地下侏罗统为例

Factors Influencing Reservoir Quality in Nonmarine Fine-grained Rocks:A case study of the Lower Jurassic in the Sichuan Basin

陆相细粒岩储层与海相细粒岩储层在物质组成、沉积环境方面差别较大,储层质量影响因素也不尽相同。以四川盆地下侏罗统为例,利用X射线衍射、氦气法测孔渗、元素地球化学、有机地化分析、扫描电镜等多种实验测试手段,分析陆相细粒岩组成成分、储层物性特征和空间类型,探讨陆相细粒岩储层质量的主控因素。研究认为,四川盆地下侏罗统细粒岩的主要组成矿物为黏土矿物、石英、碳酸盐矿物。黏土矿物与石英普遍含量较高,碳酸盐矿物局部富集。陆相细粒岩层段主要由5种岩石类型组成,包括页岩、介壳泥岩、粉砂质泥岩、粉砂岩和介壳灰岩。页岩与介壳泥岩有机质含量较高,物性较好,可作为良好的页岩气储层。陆相细粒岩储层的储集空间主要为黏土矿物片间孔和微裂缝。储层质量主要受沉积环境和成岩作用的影响,与组成成分关系较小。半深湖控制富有机质细粒岩的分布。还原、低盐度、潮湿、物源充足的沉积环境有利于细粒岩孔隙空间的发育,为储层的形成提供物质基础。黏土矿物片间孔在超压作用下保存下来,为页岩气富集提供了储集空间。

Reservoirs in nonmarine and marine fine-grained rocks differ in both material composition and sedimenta⁃ry environment,and the factors influencing reservoir quality are also different.In this study of the Lower Jurassic in the Sichuan Basin,the methods used were whole rock analysis of X-ray diffraction(XRD),He permeability,elemen⁃tal geochemistry,organic geochemical analysis,scanning electron microscopy(SEM),analysis of nonmarine finegrained rock composition,reservoir space types and microstructure.The factors controlling the reservoir quality of nonmarine fine-grained rocks are discussed.It is shown that the main minerals of the Lower Jurassic fine-grained rocks in the Sichuan Basin are clay minerals,quartz and carbonate minerals.The contents of clay minerals and quartz are high in the whole section,but the carbonate mineral content is locally enriched.The nonmarine fine-grained rocks mainly consist of five rock types:shale,shell mudstone,silty mudstone,siltstone and shell limestone.The shale and shell mudstone have high organic matter content and good shale gas reservoir physical properties.The reservoir space of the terrestrial fine-grained rock reservoir mainly consists of clay mineral interlamellar pores and microfractures,but fewer organic pores.The reservoir quality is mainly affected by sedimentary environment and diagenesis,and has little relation to its composition.Semi-deep lake conditions control the distribution of organic-rich fine-grained rocks;a reducing depositional environment of low salinity,humidity and sufficient provenance is conducive to the develop⁃ment of pore space in fine-grained rocks and provides the basic material for the formation of reservoirs.The interlami⁃nar pores in clay minerals are preserved by overburden pressure and provide storage space for shale gas enrichment.