廊固凹陷河西务构造带沙四上亚段有效储层成因机制

Genetic Mechanism of Effective Reservoirs in the Upper Part of the Fourth Member of the Shahejie Formation in Hexiwu Structural Zone of Langgu Depression

中深层有效储层成因机制一直是中深层油气勘探备受关注的内容。综合运用岩心观察、薄片鉴定、物性分析及流体包裹体分析等技术手段,研究了廊固凹陷河西务构造带沙四上亚段储层岩石学特征、储集特征及成岩作用特征,并在有效储层物性下限计算的基础上,分析了有效储层物性控制因素,总结了有效储层成因机制,建立了有效储层成因模式。研究表明:廊固凹陷河西务构造带沙四上亚段储层以岩屑质长石砂岩为主,含少量长石质岩屑砂岩,成分成熟度中等,结构成熟度高;压实作用较强,胶结作用南北差异性明显,溶解作用弱;储层储集空间以原生孔隙为主,含少量的粒内溶孔及粒间溶扩孔隙,孔渗相关性好。储层胶结物含量、分选系数、沉积微相及地层压力是廊固凹陷河西务构造带沙四上亚段有效储层形成的主要控制因素。辫状河三角洲前缘分支河道沉积环境中杂基含量少、分选好、碳酸盐岩屑含量低的细砂岩、中粗砂岩及含砾砂岩是沙四上亚段有效储层形成的有利物质基础。早期地层超压,抑制压实作用,保护原生孔隙;早期油气充注,抑制胶结作用与压实作用,保护孔隙空间。二者共同作用,是有效储层形成的主要原因。溶解作用少量增孔,颗粒边缘形成的早期石英加大抑制压实,对有效储层的形成起辅助作用。

The origin of effective reservoir in mid-deep clastic reservoir has always been the popular research content of petroleum exploration.The reservoir petrological characteristic,physical properties and diagenetic characteristics of the upper part of the Fourth Member of the Shahejie Formation（Ess4）were systematically studied through cores observation,rock thin section identification,physical properties analysis and fluid-inclusion analysis,et al in Hexiwu structural zone of Langgu depression.Moreover,the authors analyzed controlling factors of effective reservoirs on the basis of the physical properties parameter cutoff calculation,summarized the genetic mechanism and established the genetic model of effective reservoirs.The results show that the rocks of Ess4 reservoirs are mainly composed of lithic arkose and a small amount of feldspthic lithic sandstone,and they have medium compositional maturity and high structural maturity.In diagenesis,compaction is strong,cementation is obviously difference in north and south,and dissolution is weak.The reservoirs have more primary and less dissolution pores,so porosity and permeability correlation is well.Reservoir cement content,sorting coefficient,sedimentary microfacies and formation pressure are the main controlling factors of effective reservoirs.The fine sandstone,moderate coarse sandstone and pebbled sandstone with little matrix contents,well sorted,and little carbonate debris in branch channel of braided delta front are favorable material foundation in effective reservoirs forming process.Early overpressure restrained compaction and protected primary pore,also early hydrocarbon charging restrained cementation and protected pore space.They both together contributed the main reason for the formation of effective reservoir.In addition,dissolution formed a little amount of secondary pore and early quartz overgrowths around particles edge restrained compaction,which played supporting roles in the formation of effective reservoir.