A Quantitative Calculation Method of Permeability of Tight Sandstone Based on Fractal Theory

Permeability of tight porous media is crucial to characterize fluid flow in tight sandstone reservoirs. However, due to the disordered pore structures in tight porous media, how to quantitatively predict permeability of tight sandstone is an open question. In this paper, the pore size of tight sandstone was measured by SEM (scanning electron microscopy) technology. And the fractal characteristics of tight sandstone pore structure were certified. Moreover, a fractal-based permeability model with wetting phase (water) saturation was derived to analyze the influence of capillary tortuosity fractal dimension, pore fractal dimension and wetting phase saturation on permeability and porosity of tight sandstone. The research results show that pore structure parameters (e.g., tortuosity fractal dimension and pore fractal dimension) and wetting phase saturation have significant impacts on the rock permeability and porosity. Porosity of porous media increases with the increasing of tortuosity fractal dimension, while permeability decreases as tortuosity fractal dimension increases. Porosity and permeability increase with the increase of pore fractal dimension. However, permeability of tight porous media decreases with the increase of wetting phase saturation. Especially, when wetting phase saturation is greater than 65%, permeability will decline sharply as water saturation increases. The derived model in this paper can provide an insight into wetting phase saturation influencing permeability of tight sandstone.