CHARACTERIZATION OF MICROSCOPIC PORE STRUCTURE IN THGHT SANDSTONE RESERVOIR: A Case Study of Yanchang Formation in Southeastern Ordos Basin

Micro-pore throat structure is one of the important factors controlling the storage capacity and fluid flow of tight sandstone reservoir. Selecting 20 representative samples from tight sandstone reservoir of the Late Triassic Yanchang Formation in southeastern Ordos Basin, the study carries out a series of experiments, including cast thin section, scanning electron microscope, high pressure mercury injection and reservoir petrophysical test, applying fractal theory to realize the characteristics of pore throat structure, and analyzes the relationship between fractal dimensions and physical properties, pore throat structure parameters and mineral content. The results show that the pore throat structure of the samples can be divided into mesopore and micropore according to fractal curves. Based on the calculated corresponding fractal dimension, it is inferred that the mesopore contributes to most of the porosity and permeability. The fractal dimension of mesopore has good correlation with the parameters of reservoir physical properties and pore structure. The larger the fractal dimension is, the more uneven the pore distribution is, with worse connectivity and more heterogeneity. Despite the support of quartz and chlorite to micropore and mesopore, chlorite could anyway cause severe mesopore blockage. The dissolution of feldspar increases the number of micropores, meanwhile increases the heterogeneity of reservoir to a certain extent.