ABSTRACT
Spontaneous capillary imbibition is a kind of ubiquitous transport phenomenon, and it is of great significance to define displacement process and transport in the field of reservoir recovery, soil physics and building materials. In the process of imbibition, the capillary suction is used to suck the wet liquid into the porous medium, and the imbibition height is closely related to the tortuosity of the capillary in the porous medium. The tortuosity of capillary in porous media is related to porosity and microstructure of medium, and it is important to describe the flow characteristics of fluid through porous media. The classical L-W law shows that the position of the wetting front position changes linearly with the square root of the time in the capillary and porous media. The model does not consider the effect of the bending effect of the capillary on the imbibition, and ignores the pore structure of porous media, such as connectedness, tortuosity and pore size distribution. The results of the imbibition experiment for different porous media show that the imbibition phenomenon is not subject to the classical L-W law. In order to explain this phenomenon, scholars have modified L-W law and introduced time exponent to propose a time-fractal model. In this paper, neutron radiography technology was used, as a powerful imaging tool, to observe the dynamic evolution of wetting front in sandstone and analyze the sorptivity of sandstone. Applying high-resolution X-ray computed tomography and mercury intrusion porosimetry, porosity, volume fractal dimension, and curvature were obtained. According to these parameters, the time-fractal model was used to estimate the sorptivity of sandstone and predict the dynamic migration of wetting front. Finally, we compare the predicted data with the experimental data, prove the validity of the time-fractal model, and discuss the superiority and accuracy of the model.
