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孔隙结构特征及类型划分对低渗透储层勘探开发至关重要,基于多重分形理论与核磁共振实验,对东营凹陷南坡沙河街组沙四段(ES4)复杂低渗透砂岩进行孔隙结构研究。首先,根据岩心物性、铸体薄片、压汞等资料所反映的孔隙结构参数差异,将研究区的岩石孔隙结构类型划分了3大类5小类;然后,针对不同类型岩石的核磁共振T_2谱进行插值并计算其对数坐标下的一维、三维分形维数以及多重分形谱,并提取多重分形参数奇异性强度α、分布稠密度f(a),结果显示孔隙结构类型不同,盒维数尤其是多重分形参数值差异明显,孔隙结构好,其a、f(a)偏向高值,以此划分孔隙结构类型与压汞、薄片分析结果基本一致;最后,将该方法应用到核磁共振测井剖面上,应用效果较好,表明多重分形是核磁共振T_2谱的一种属性,利用核磁测井T_2谱多重分形特征及参数能够连续较好地评价低渗透砂岩孔隙结构类型与预测有效储层。
Pore structure and type classification are very important for the exploration and development of low permeability reservoirs. Based on multifractal theory and NMR experiments, the pore structure of the ES4 complex low permeability sandstone on the southern slope of Dongying depression is studied. First of all, according to the difference of pore structure parameters reflected by the petrophysical properties, casting thin sheets and mercury intrusion, the types of pore structures in the study area are divided into three categories and five sub-categories. Then, the T 2 spectra of different types of rocks The fractal dimension and the fractal dimension of one-dimensional, three-dimensional and logarithmic coordinates were calculated and the singular intensity α and distribution density f (a) of the multifractal parameters were extracted. The results showed that the pore structure types were different and the box dimension In particular, the values of multifractal parameters are obviously different, the pore structure is good, and the values of a and f (a) tend to be high, and the types of pore structures are basically the same with those of mercury intrusion and flake analysis. Finally, the method is applied to the nuclear magnetic resonance Well section, the application effect is good, indicating that the multifractal is an attribute of NMR T_2 spectrum. By using the multifractal characteristics and parameters of T_2 NMR logging, it is possible to evaluate the pore structure type of low permeability sandstone and predict the effective reservoir .