利用高压压汞实验研究致密砂岩孔喉结构分形特征

微观孔喉结构是影响砂岩油藏特征的重要因素，但致密砂岩孔喉复杂，非均质性强，常规测试难以对其进行有效表征，需要利用分形理论对致密砂岩孔喉结构进行深入研究。以鄂尔多斯盆地姬塬地区长7段致密砂岩为研究对象，通过高压压汞和分形理论研究了致密砂岩孔喉结构和分形维数特征。讨论了分形曲线转折点与孔喉结构关系，并结合铸体薄片和扫描电镜，分析了孔喉分形特征形成原因。结果表明:致密砂岩分形曲线具有明显转折点。转折点为孔喉分布峰值，代表连通性好的大尺度孔喉向连通性差的小尺度孔喉的转换。致密砂岩小尺度孔喉分形维数平均值为2.24，大尺度孔喉半径分形维数平均值为4.65。大尺度孔喉非均质性明显强于小尺度孔喉。小尺度孔喉分形维数与孔喉结构相关性较好。致密砂岩小尺度孔喉主要为喉道和晶间孔，这部分孔喉连通性差，半径较小，受成岩作用影响微弱，因此分形维数小。致密砂岩大孔喉主要为剩余粒间孔和溶蚀孔隙，该类型孔喉半径较大，受成岩作用改造明显，因此分形维数大。 

Fractal characteristics of pore-throat structure in tight sandstones using high-pressure mercury intrusion porosimetry

Microcosmic pore-throat structure is an important factor affecting the characteristics of sandstone reservoirs.However, the pore-throat of tight sandstone is complex and heterogeneous, which is difficult to be effectively characterized by conventional tests.Therefore, it is necessary to use fractal theory to research the pore-throat structure of tight sandstone.In this study, through high-pressure mercury injection porosimetry and fractal theory, the pore-throat structure and fractal dimension characteristics of the Chang 7 tight sandstones in Jiyuan area of the Ordos Basin are studied, and the relationship between infection points on the fractal curves and pore-throat structure are discussed.And combined with casting thin section and scanning electron microscope, the causes of fractal characteristics from pore-throat are analyzed.The results show that there are obvious infection points on fractal curves, and the infection point is the peak value of pore size distribution, which representes the transition from the large pore-throat with good connectivity to the small pore-throat with poor connectivity.The average fractal dimension of small pore-throat is 2.24, and that of large pore-throat is 4.65.The heterogeneity of large pore-throat is obviously stronger than that of the small pore-throat.And the correlation between fractal dimensions of small pore-throat and pore-throat structure is good.The small pore-throats of tight sandstones mainly consist of intercrystalline pores and throats, which have poor connectivity, small radius and weak influence by diagenesis.Therefore, the fractal dimensions of the small pore-throat are low.The large pore-throats of tight sandstone mainly consist of residual intergranular pores and dissolution pores.The large pore-throat has good connectivity, large radius and obvious transformation by diagenesis.Therefore, the fractal dimension of the large pore-throat is high.