Analyses based on thin section,SEM,mercury intrusion and logging data were combined with outcrop and core observations to study the characteristics and diagenesis of tight sandstone reservoirs in the fourth member of the Xujiahe Formation in northern Sichuan Basin.The results show a calcareous sandstone-dominated west part,a lithic sandstonedominated north part and a feldspar/lithic sandstone-dominated east part,in the area of interest.The rock type zoning was found to be closely linked to the distribution of the three provenances at the periphery of northern basin.Physical properties can be summarized as ultra-low porosity and permeability.Types of pores were mainly secondary solution pores with small diameter and fine throat and micro fractures.Diagenesis were complicated and varied from compaction and pressure solution,to cementation,dissolution,replacement and alteration as well as fracturing.And all the processes had once played important roles in the formation of ultra-low permeability tight sandstone reservoirs.Compaction caused loss of primary pores by 77.52 ％ and cementation destroyed reservoir properties through porosity reduction by 30％.Dissolution generated secondary pores and increased porosity by 3.28 ％.Later tectonic activities also helped shaping the reservoirs with secondary solution pores-fractures being the main accumulation space.%通过薄片、扫描电镜、压汞及测录井资料分析,结合野外剖面调查和岩心观测等手段,对四川盆地北部须家河组四段致密砂岩储层特征及成岩演化规律进行了研究.结果表明:研究区西部主要发育钙屑砂岩储层,北部主要发育岩屑砂岩储层,东部主要发育长石岩屑砂岩储层,岩石类型的分区性与盆地北部周缘三物源体系分布息息相关;储层物性表现为特低孔、特低渗的特征,孔隙类型以次生溶孔和微裂缝为主,以小孔、细吼为主要特征;储层成岩作用类型复杂,主要有压实压溶作用、胶结作用、溶蚀作用、交代蚀变作用和破裂作用.多种类型的成岩作用在特低渗透致密砂岩储层形成过程中扮演着重要角色.其中,压实作用是造成原生孔隙损失的最主要因素,使储层孔隙度损失77.52％左右;胶结作用破坏储层物性,使孔隙度损失30％左右;溶蚀作用形成次生孔隙,增加孔隙度3.28％;后期构造作用对储层有建设性影响,进而形成现今以次生溶孔-裂缝为主要储集空间的致密砂岩储层.
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