川西坳陷中部须家河组五段致密砂岩储层特征及主控因素

利用岩心观察、测井资料、物性分析、薄片鉴定、扫描电镜等手段，对川西坳陷中部须家河组五段（须五段）储层特征及相对优质储层的影响因素进行探索。研究认为，须五段致密储层砂岩为赋存于烃源层系中单层厚2~25 m的三角洲前缘水下分流河道、河口坝、席状砂及浅湖砂坝砂体，为特低孔低渗储层，孔隙度平均为2.06%，渗透率平均为0.162×10^-3 μm²；塑性颗粒、粘土杂基的高含量，碳酸盐矿物胶结物的大量发育，是须五储层岩性致密化的主要因素；相对强水动力条件下沉积的中-细粒钙屑砂岩、含碳酸盐岩屑砂岩利于原生孔隙的保存及溶蚀流体交换，形成相对优质储层；易溶矿物长石含量极低，应是长石被溶蚀后的结果，并形成少量的溶蚀孔隙；烃源层系中独有的生烃增压缝利于大量有机酸进入胶结物未充满的残余粒间孔，再次发生溶蚀扩大。因此，与优质烃源岩相邻的具有一定厚度的水下分流河道及河口坝砂体是钻探的首选目标。

Characteristics and controlling factors of tight sandstone reservoirs in the 5th member of Xujiahe Formation in the central of western Sichuan Depression

Characteristics and dominant controlling factors of tight sandstone reservoirs in the 5th member of Xujiahe Formation in the central of western Sichuan Depression was researched through core observation,logging interpretation,phy-sical property analysis,thin section examination and scanning electron microscope,in order to provide the basis for deployment of exploration and development of new sequences.The tight sandstone reservoirs occur in the 5th member source rocks and consist of delta front underwater distributary channels,channel bars,sheet sand and shallow lake sand bars,with single layer thickness ranging from 2 to 25 m.They belong to super-low porosity and low permeability reservoirs,with an average porosity of 2.06% and permeability of 0.162×10^-3 μm² respectively.High contents of plastic particles,clay matrix and carbonate cements are the principal factors that led to the densification of the 5th member reservoirs.The medium-fine grain calcarenaceous sandstones and carbonate lithic sandstone deposited in relatively stronger hydrodynamic environments are favorable for the preservation of primary pores and exchange of fluids,thus are reservoirs with relatively high quality.Dissolution of feldspar resulted in the low content of feldspar and the formation of some dissolution pores.And the unique cracks caused by hydrocarbon generation pressurization in source rocks were helpful for the organic acid to enter into the residual inter-granular pores,enlarging pre-existing dissolution pores.Therefore,the delta front underwater distributary channels and channel bars sandbodies adjacent to the source rock with a certain range of thickness are the most favorable targets for tight sandstone reservoirs exploration.