渤海湾盆地歧北斜坡沙河街组储层特征及形成机理

Characteristics and forming mechanisms of reservoirs in the Shahejie Formation of Qibei slope,Bohai Bay Basin

利用普通薄片、铸体薄片、扫描电镜等实验数据，结合测井资料，分析了渤海湾盆地歧北斜坡沙河街组储层岩石成分、孔渗分布、孔隙结构及储层品质指数（ RQI）等特征，探讨了储层形成机理。研究结果表明，沙河街组砂岩成熟度较低，孔隙类型多样，孔隙结构以Ⅳ类为主，孔喉为细－微孔小喉，以次生粒间孔为主，属于典型的低孔低渗储层。储层形成的主控因素有沉积作用、次生溶蚀作用及深部异常高压等。水道沉积环境控制储集岩的碎屑粒度、胶结物性质及含量、孔隙的孔喉半径和分选系数等，水道主体砂岩比侧缘砂体孔隙度高出3％～5％，且厚度较大，易形成良好的储集层。压实作用和胶结作用使原生孔隙消失殆尽，砂岩中长石等的溶蚀作用造成了次生孔隙的发育，为储集空间的主要贡献者。异常压力的发育抑制了压实作用，促进了溶蚀作用，起到了增加储层孔隙的作用。综合分析认为，重力流水道和扇三角洲前缘相带中的次生溶蚀发育带是储层发育的有利区带。

Experimental means , including ordinary slices , casting sections and electron microscope , were used to study samples from reservoirs in the Shahejie Formation of Qibei slope in Bohai Bay Basin .The results were then combined with logging data to analyze the features（lithological composition,porosity and permeability distribution,pore texture and re-servoir quality index （ RQI） ） and forming mechanism of the reservoirs .The analyses show that the sandstone reservoirs in the formation are typical low-porosity and low-permeability reservoirs featuring in low maturity ,various types of pores ,Ⅳtype of pore structure ,small-to micro-sized pore throat and secondary intergrannual pores .The forming mechanisms of the reservoirs include sedimentation ,secondary dissolution and deep overpressure .It also indicates that sedimentary setting of the channels controlled the particle size ,cement properties and content ,pore throat size and sorting coefficient of the re-servoirs.Sandstone in the main channels offered better conditions for the forming of reservoirs as it is thicker and has a porosity of 3%-5%higher than that at the side edges .Primary pores in the reservoirs were almost killed during compac-tion and cementation , while dissolution of feldspar and other minerals created secondary pores and provided reservoir space .Overpressure in the reservoirs restrained compaction but boosted dissolution and enlarged reservoiring space .A comprehensive analysis of all the information suggests that secondary pore zones in gravity flow channels and fan delta fronts be the most favorable locations for reservoirs to develop .