鄂尔多斯盆地延长组致密砂岩孔喉结构与油藏物性表征

基于高压压汞和核磁共振测试方法，结合分形理论对鄂尔多斯盆地延长组致密砂岩孔喉结构与油藏物性进行了表征。采用毛管束模型和润湿相模型计算了高压压汞孔喉分形维数，利用核磁共振测试T₂谱分别计算了大孔、中孔、小孔以及总孔隙的分形维数；对各分形维数与油藏物性之间的关系进行了对比分析。研究表明：基于高压压汞曲线计算岩心分形维数时，相比于润湿相模型，毛管束模型计算得到的分形维数与油藏物性之间具有更好的相关性，随着分形维数增加，平均半径减小，孔喉结构非均质性增强，油藏物性变差。核磁总孔隙分形维数与油藏物性相关性较差，大孔和中孔的分形维数与油藏物性具有较好的相关性，其中随着大孔和中孔分形维数增加，岩心渗透率降低，油藏物性变差；与小孔相比，大孔和中孔的分形维数与油藏物性的相关性更强，表明致密砂岩储层物性主要受大孔和中孔控制，分形维数可以有效表征致密砂岩小孔、中孔和大孔对油藏物性的影响。

Characterization of Pore Structure and Petrophysical Properties of Tight Sandstone of Yanchang Formation,Ordos Basin

Based on fractal theory, the pore structures of tight sandstone of Yanchang Formation in Ordos basin were characterized by high pressure mercury intrusion (HPMI) and nuclear magnetic resonance (NMR). The fractal dimension from mercury intrusion capillary pressure was calculated by 3D capillary tube model and wetting phase model, the fractal dimensions of macropores, mesopores, micropores and total pores from NMR T₂ spectra were calculated by NMR model, and the correlations between the calculated fractal dimension and petrophysical properties were analyzed. The research results show that the fractal dimensions calculated by mercury capillary pressure and capillary tube model have a better correlation with the petrophysical properties than those by wetting phase model. With the increase of fractal dimension, the median pore radius decreases, the pore structure heterogeneity increases, and the petrophysical properties of tight sandstone become worse; the fractal dimensions of total pores are poorly correlated to tight sandstone petrophysical properties. After the pore size ranges are divided into macropores, mesopores,and micropores, the calculated fractal dimensions of macropores and mesopores are strongly correlated to tight sandstone petrophysical properties compared to micropores, and the petrophysical properties become worse with the increase of the fractal dimensions of macropores and mesopores. It shows that tight sandstone petrophysical properties are mainly dominated by macropores and mesopores, and the fractal dimension can effectively characterize the influence of micropores, mesopores, and macropores on the tight sandstone petrophysical properties.