| Summary: | 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.
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