深层砂岩储层成岩作用差异性及与储层质量的关系——以准噶尔盆地中部征沙村地区侏罗系为例

Different diagenesis of deep sandstone reservoir and its relationship with reservoir property:Case study of Jurassic in Zhengshacun area,central Junggar Basin

为认识深层碎屑岩储层质量的控制因素及有效储层分布规律,以准噶尔盆地中部征沙村地区下侏罗统三工河组砂岩储层为例,利用岩心样品的铸体薄片、扫描电镜、碳氧同位素、X?射线衍射及常规物性测试手段,研究了储层岩石学和成岩作用特征,讨论了成岩作用对不同类型储集岩石相的影响,并建立了岩石相—沉积微相的联系。结果表明:研究区三工河组砂岩成分成熟度低,主要为长石岩屑砂岩,自生矿物包括碳酸盐、自生黏土、硬石膏及硅质等;总体为低—特低孔渗性储层,非均质性强。依据岩石学组构和成岩作用差异,可将储集砂岩主要划分为极细—细粒富塑性颗粒砂岩、方解石胶结砂岩和中—细粒贫塑性颗粒砂岩。不同岩石相经历了差异性成岩作用:其中富塑性颗粒砂岩表现为强压实、弱胶结和弱溶蚀特征;方解石胶结砂岩则表现为强胶结、弱压实和弱溶蚀特征,二者均在成岩阶段早期致密化;贫塑性颗粒砂岩表现为中等压实、弱—中等胶结、强溶蚀。成岩阶段早期压实作用和胶结作用程度低,不但能保留原生孔隙,亦能遭受后期深埋阶段的酸性流体改造,形成深层物性较好的有效储集岩。不同岩石相的分布总体受沉积微相控制,物性最佳的贫塑性颗粒砂岩主要分布在分流河道中下部或河口坝中上部,这种分布模式将为寻找深层有效储层提供指导。

To recognize the factors which controlled the deeply buried clastic reservoir quality and the distribution of effective reservoirs,the paper takes sandstone reservoirs of the Lower Jurassic Sangonghe Formation in Zhengshacun area,central Junggar Basin as an example for study.Based on the thin sections of core samples,scanning electron microscopy,carbon-oxygen isotopes(C-O isotopes),X-ray diffraction,porosity and permeability,the paper studies the characteristics of petrology and diagenesis of reservoirs,discusses the effects of diagenesis on different lithofacies,establishes the relationship between lithofacies and sedimentary microfacies.The results show that the sandstones of Sangonghe Formation are feldspathic litharenite,and the compositional maturity is really low.The authigenic minerals include carbonate cementation,authigenic clay minerals,anhydrite and siliceous cementation.It is generally a low-ultra-low porosity and permeability reservoir with strong heterogeneity.According to the difference of petrology and diagenesis,sandstones can be divided into three lithofacies:ductile-rich sandstone,calcite-cemented sandstone and ductile-lean sandstone.Different lithofacies undergoes different diagenesis.Ductile-rich sandstone is characterized by strong compaction,weak cementation and dissolution,while calcite-cemented sandstone is characterized by strong cementation,weak compaction and weak dissolution,and the type of sandstones densified during the early diagenesis.Ductile-lean sandstone is moderately compacted,weakly-moderately cemented and strongly dissolved.For the lower degree of compaction and cementation during the early diagenesis,it can not only retain more primary pores,but also be dissolved by acid fluid in the later deep burial,thus forming effective reservoir rocks with good porosity in deep layers.The distribution of different lithofacies is generally controlled by sedimentary microfacies,and ductile-lean sandstone with the best porosity mainly distributes in the middle and lower part of distributary channel or the middle and upper part of mouth bar.This distribution pattern will provide guidance for exploring deep effective reservoirs.