典型致密砂岩气储层孔隙结构分类及其意义——以鄂尔多斯盆地盒8段为例

Classification of pore structures in typical tight sandstone gas reservoir and its significance:A case study of the He8 Member of Upper Palaeozoic Shihezi Formation in Ordos Basin,China

在分析目前储层孔隙结构分类方法的基础上,根据鄂尔多斯盆地盒8段265块典型致密气储层砂岩样品的压汞测试数据,提出了适应于盒8段致密砂岩气储层孔隙结构的分类方案。分类鉴于反映孔隙结构的参数间信息具有一定的重迭,聚类分析前,利用Q型主因子分析将优选出的孔隙度(φ)、渗透率(K)、排驱压力(Pd)、中值压力(P50)、中值半径(R50)、分选系数(Sp)和最大进汞饱和度(Smax)等7个孔隙结构参数提取为3个主因子,依据主因子所涵盖的综合信息特征,分别命名为孔喉大小因子、孔渗因子及孔喉分选因子。以3个主因子作为聚类分析的新变量,并结合毛管压力曲线特征、镜下孔隙特征等,将典型致密气砂岩孔隙结构划分为4种类型。运用Fisher判别法对聚类结果进行了回符检验,判别正确率达87.5%。在此基础上,建立了定量的典型判别函数来划分孔隙结构类型:Ⅰ型(Y_1>2.51),Ⅱ型(Y_1=-0.12~2.51),Ⅲ型(Y_1=-3.72^-0.12)和Ⅳ型(Y_1<-3.72)。研究结果表明:Ⅰ型或Ⅱ型孔隙结构的致密砂岩气储层为有利储层,据此分类与试气结果十分吻合,可对今后寻找有利储层、致密气的规模勘探开发提供有效地质依据。

Based on the existing classification methods of reservoir pore structure and 265 samples of mercury injection experiments from the tight gas reservoir of Upper Palaeozoic He 8member in Ordos Basin,this paper discussed the classification of pore structures in typical tight sandstone gas reservoir.Considering that certain overlaps exist between the pore structure parameters which reflect the classification information,three factors were extracted from the seven parameters including porosity（Φ）,permeability（K）,displacement pressure（Pd）,median pressure（P50）,median pore throat radius（R50）,sorting coefficient（Sp）and maximum mercury saturation（Smax）using Q-model principal factor analysis.According to comprehensive information characteristics from the main factors,three main factors were named as pore throat size factor,porosity-permeability factor and pore throat sorting factor,respectively.Taking the three principal factors as cluster new variables,combining characteristics of capillary pressure curve and arthroscopic characteristic,pore structures of typical tight sandstone gas reservoir are divided into four types.Through Fisher discriminant method,the correct discrimination rate of clustering results can reach 87.5%,and accordingly,discriminant functions are established to divide the type of pore structure：TypeⅠ（Y1〉2.51）,TypeⅡ（Y1=-0.12-2.51）,TypeⅢ（Y1=-3.72--0.12）,and TypeⅣ（Y1〈-3.72）.The results show that TypeⅠand TypeⅡ pore structures are in most favor of tight sandstone gas reservoir,and they also present that this classification is consistent with the test gas data.It will also provide solid geological evidence for high quality reservoirs and further regional exploration and development of tight gas in the Ordos Basin.