致密砂岩储层微观孔喉结构及其分形特征

Micro Pore Throat Structure and Fractal Characteristics of Tight Sandstone Reservoir

孔喉微观结构定量评价一直是致密砂岩储层研究的热点和难点。以分形维数为突破口,在鄂尔多斯盆地子长地区不同井中采集了上三叠统延长组长6段12个岩心样品,通过扫描电镜、铸体薄片、高压压汞等实验方法以及分形理论对致密砂岩样品的孔喉结构及其分形特征进行了研究。结果表明,研究区致密砂岩储层的孔隙类型主要由剩余粒间孔、溶孔和晶间孔组成。总分形维数与孔隙度和渗透率存在良好的负相关性,表明研究区致密砂岩储层孔喉结构的复杂程度和非均质性对物性具有一定的影响。中孔的分形维数与孔喉结构参数的相关性更好,表明中孔的非均质性和表面粗糙度主要影响储集空间和渗流性质。致密砂岩储层的品质与分形维数呈明显的负相关关系,越有利于油气富集的储层,其分形维数越小。

The quantitative evaluation of pore throat microstructure has always been a hot and difficult point in the study of tight sandstone reservoirs.Taking fractal dimension as a breakthrough point,12 core samples of Chang 6 Member of Yanchang Formation of Upper Triassic were collected from different wells in Zichang area of Ordos basin.The pore throat structure and fractal characteristics of tight sandstone samples were studied by means of scanning electron microscope,casting thin section,high pressure mercury injection and other experimental methods and fractal theory.The results show that the pore types of tight sandstone reservoirs in the study area are mainly composed of residual intergranular pores,dissolution pores and intercrystal pores.There is a obvious negative correlation between total fractal dimension and porosity and permeability,which indicates that the complexity and heterogeneity of pore throat structure of tight sandstone reservoirs in the study area have a certain impact on the physical properties.The correlation between the fractal dimension of mesopores and pore throat structure parameters is better,which indicates that the heterogeneity and surface roughness of mesopores mainly affect the reservoir space and seepage properties.There is a positive correlation between the quality of tight sandstone reservoir and the fractal dimension.The more favorable the reservoir is for oil and gas enrichment,the smaller the corresponding fractal dimension is.