Pore-throat structure complexity of Yan’an Formation reservoir in Tiebiancheng area and its controlling effect on oil saturation

In order to further guide the exploration and development of oil reservoirs in Tiebiancheng area, the pore throat structure and its complex characteristics of typical samples in Yan 8-Yan 10 layers were quantitatively analyzed by using experimental methods such as high-pressure mercury injection, scanning electron microscopy, cast thin section, fluorescence observation, oil saturation test and fractal theory, and the control effect of pore throat structure on oil content was discussed. The results show that the Yan 8-yan 10 reservoirs in Tiebiancheng area is mainly composed of lithic sandstone, and the pore types are mainly intergranular pores and feldspar dissolved pores, with micron sized pores widely developed. The average porosity is 14.54% and the average permeability is 0.24×10^-3 μm², belonging to medium porosity ultra-low permeability reservoir. The pore throat structure of low permeability reservoir is complex. The larger the sample storage space in this area, the higher the complexity of pore throat structure, which is mostly a combination of large pore and fine throat. The pore throat structure has three fractal segments, which corresponds to the large, medium and small pore throat segments in turn. The average fractal dimensions of each segment are 2.8535, 2.4358 and 2.4491, respectively. Although the reservoir capacity of the large pore throat section is high, it does not determine the overall oil saturation of the low-permeability reservoir. The more developed the macropore coarse throat combination, the more homogeneous the distribution of the mesopore throat, which is more conducive to the enrichment of oil in low-permeability reservoirs. The radius range of pore throat which is most conducive to oil and gas enrichment is 0.02~1 μm. The research results provide a key scientific basis for further optimizing the oil and gas development strategy in the Tiebiancheng area.