FRACTAL ANALYSIS OF PORE STRUCTURES IN LOW PERMEABILITY SANDSTONES USING MERCURY INTRUSION POROSIMETRY

Pore structures of low permeability sandstones collected from the Yanchang Formation in the Ordos Basin of China were analyzed using mercury intrusion porosimetry (MIP) with fractal theory. Six different fractal models were applied to calculate the fractal dimension from mercury intrusion capillary pressure (MICP), and the relationships between the calculated fractal dimensions and the sandstone petrophysical properties were analyzed. The results show that low permeability sandstones have obvious fractal characteristics, and the fractal dimensions calculated from the 3D capillary tube model have the strongest correlations with petrophysical properties and are most suitable for analyzing pore structures. The fractal dimensions of all the pores have strong and positive correlations with the fractal dimensions of small pores but have no obvious correlation with the fractal dimensions of large pores. Compared with the modified Winland model, fractal permeability models can accurately predict the permeability of low permeability sandstones.