查干凹陷下白垩统扇三角洲相储层特征及物性影响因素

摘要

为了阐明查干凹陷下白垩统储层特征及其对储层物性影响，应用岩心、薄片及储层分析资料，通过储层岩石学特征、沉积作用和成岩作用分析，表明下白垩统扇三角洲砂体由岩屑长石砂岩和长石岩屑砂岩构成，具有低成分成熟度、低结构成熟度和高胶结物含量的“两低一高”特征，为近源、快速堆积成因。储层物性整体较致密，属于特低孔－特低渗透型（孔隙度平均为6.3％，渗透率平均为7.78×10－3μm2），发育细－微喉，储集空间以残余原生粒间孔和粒间溶孔为主，主要受控于碎屑粒径、压实程度、碳酸盐含量及有机酸来源。有利储层主要分布于扇三角洲前缘水下分流河道砂（砾）岩中，其次是席状砂和河口坝沉积的细砂岩。纵向上，次生孔隙发育带发育在2100～2800 m，对应有机质成熟阶段，释放大量的有机酸对砂岩长石颗粒和碳酸盐胶结物发生强烈溶蚀，扩大粒间和粒内孔隙，有效改善储层质量。因此，优势沉积微相、强溶蚀带及次生孔隙发育带是有利储层的主控因素。%In order to reveal the reservoir characteristics and their influences on poroperm characteristics of the Lower Cretaceous in Chagan Depression,core,thin-section,and reservoir analysis data were utilized to research the petrological characteristics,sedimentation and diagenesis of the reservoirs.The results show that the sandbodies of fan-delta facies in the Lower Cretaceous consist of lithicarkose and feldspathic litharenite with low compositional maturity, low maturity structure and high cement content,which are originated from proximal and rapid accumulation.The reservoir is relatively tight as a whole and is of ultra-low porosity and permeability reservoir type( with average porosity of 6.3%and permea-bility of 7.78 ×10 -3 μm2 ) .Thin-tiny throats are well developed and the reservoir spaces are dominated by residual pri-mary and dissolved intergranular pores,and their development are controlled by particle size,compaction,cementation, content of carbonate and the origin of organic acid.The favorable reservoir is mainly distributed in the sandstones( con-glomerates) of the subaqueous distributary channel of fan delta front,followed by fine sandstones in sand sheet and mouth bar.Vertically,the secondary porosity zone is mainly developed in the depth interval of 2 100 -2 800 m,which corre-sponds to the maturity stage of organic matters.The mature organic matter released large amount of organic acid which strongly dissolved the feldspar particles and carbonate cement,enlarged intergranular and intragranular pores and effec-tively enhanced reservoir quality.Obviously,favorable sedimentary microfacies,strong dissolution zone and secondary po-rosity zone are the main factors controlling favorable reservoir distribution.