Influence of pore structure of tight sandstone reservoirs on fluid mobility and comprehensive characterization

ObjectiveReservoir fluid mobility is significantly influenced by the combined effects of reservoir physical properties and pore structure, and cannot be accurately characterized by a single parameter. This study aims to apply a comprehensive pore structure characterization to evaluation tight sandstone reservoirs. MethodsIn this study, the effective movable fluid porosity $(\varphi_{\mathrm{cutoff}}) $ and effective movable fluid pore throat radius $(r_{\mathrm{cutoff}}) $ were calculated by integrating nuclear magnetic resonance (NMR) and high-pressure mercury intrusion (HPMI) with fractal theory for the Triassic Chang 82 tight sandstone reservoir in the Heshui area of the Ordos Basin. To explore the relationship between pore structure parameters and the degree of fluid mobility in the reservoir, principal component analysis (PCA) was employed to extract factors, and k-means clustering was introduced to establish a comprehensive evaluation approach for fluid mobility of tight sandstones. ResultsThe results showed that the pore throat types of the target layer in the study area were predominantly medium-small pores and medium-fine throats, and movable fluid mainly resided in pores with pore sizes of 0.01-1.0 μm. The fractal dimension ranged from 2.4400 to 2.7412, with an average of 2.55. The effective movable fluid pore throat radius ranged from 0.016 to 0.095 μm, with an average value of 0.049 μm. The effective movable fluid porosity ranged from 0.716% to 2.980%, with an average value of 1.598%. By integrating parameters of fluid mobility, physical properties, and pore structure, four principal components were extracted to evaluate reservoir permeability and storage capacity, microscopic heterogeneity, production capacity, and the proportion of large pore throats. Based on the clustering results from the first three principal components, the samples were classified into Class Ⅰ, Ⅱ, and Ⅲ. ConclusionThe comprehensive evaluation results of fluid mobility can provide a basis for reservoir evaluation and efficient development of similar tight sandstone oil reservoirs.