沉积和成岩因素对碎屑岩储集层质量贡献率的定量分析方法——单因素比较法*

碎屑岩储集层质量在此指其渗透率和孔隙度。影响储集层质量的因素主要是沉积方面和成岩方面。沉积方面的因素包括粒度、磨圆度、分选系数和杂基含量等,成岩方面的因素包括压实强度、溶蚀孔隙含量、胶结物类型和含量等。一种砂岩储集层的质量往往是多种单因素共同作用的结果,如何理清每个因素的具体贡献率是确定主控因素的关键。作者提出了一种分析各种沉积和成岩因素对储集层质量定量贡献率的方法——单因素比较法,并以渤中凹陷古近系东营组砂岩为例进行了演示分析。该地区东营组三角洲平原分流河道砂岩与三角洲前缘河口坝砂岩储集物性差异巨大,计算了各个因素对这种差异的贡献率,确定了主控因素:杂基含量差异的贡献率为78.5%,是主控因素;粒度差异的贡献率为2.7%,分选系数差异的贡献率为1.5%,自生黏土矿物含量差异的贡献率为15.9%,碳酸盐胶结物含量差异的贡献率为2.3%,溶孔含量差异的贡献率为1.5%,压实强度差异的贡献率为1.7%。沉积因素的综合贡献率为各沉积单因素的贡献率之和,为82.7%;成岩因素的综合贡献率为各成岩单因素的贡献率之和,为18.4%(其中溶孔的影响与其他因素相反,即为-1.5%)。因此,沉积因素是导致该储集层质量差异的主要因素。

Contribution of sedimentary and diagenetic factors to clastic reservoir quality: Quantitative determination by single factor comparison method

Quality of clastic reservoirs refers to permeability and porosity. Factors controlling reservoir quality are mainly sedimentary and diagenetic. Sedimentary factors include grain size,rounding,sorting and content of clay matrix. Diagenetic factors include compaction degree,content of dissolution pores,type and content of cements. The reservoir quality of a sandstone is commonly controlled by many factors,and the key to determine major controlling factors is to find out quantitative contribution of each factor. In this paper,a method to analyze quantitative contribution of sedimentary and diagenetic factors to reservoir quality—the single factor comparison method—is proposed out,and is applied to the sandstone reservoirs in the Dongying Formation of Paleogene in the Bozhong sag. There are two types of sandstones in the Dongying Formation,distributary channel sandstone and mouth bar sandstone of deltaic facies,and their permeability differs greatly. Quantitative contribution rate of each factor to the reservoir quality difference is calculated,and major controlling factor is determined:Contribution rate of clay matrix content is 78.5%,indicating clay matrix content is the major controlling factor;that of grain size is 2.7%,that of sorting coefficient is 1.5%;that of authigenic clay mineral content is 15.9%,that of carbonate cement content is 2.3%,that of dissolution pore content is 1.5%,that of compaction degree is 1.7%. Comprehensive contribution rate of sedimentary factors is the sum of each sedimentary factor??s contribution rate,i.e., 82.7%;comprehensive contribution rate of diagenetic factors is the sum of each diagenetic factor’s contribution rate,i.e., 18.4%(the rate of dissolution pore is -1.5% because of its reverse influence). Thus,sedimentary factors are major factors resulting in great difference in permeability between channel sandstone and mouth bar sandstone in this area.