Neutron radiography study of water spontaneous imbibition in unsaturated sandstone

The spontaneous imbibition of water in variable saturated porous media is a common phenomenon in various geotechnical applications. The relationship between the traveled distance of wetting front and imbibition time can be characterized by the sorptivity however, few researches have been carried out to investigate the sorptivity model in the spontaneous imbibition process. In this paper, based on the fractal dimension of pore mass and the formula of total flow rate of cross section of medium without considering gravity, a model was derived to calculate the sorptivity of sandstone. To validate the model, quantitative data on the imbibition of water in the matrix of unsaturated sandstone were obtained by neutron radiography a powerful imaging tool to research the dynamic water imbibition behaviour in rocks. The consequences display that there is the obvious linear relation between the traveled distance of wetting front and the square root of imbibition time in four monitoring lines and the linear coefficient is regarded as the experimental value of the sorptivity. Compared the mean of the experimental value, the theoretical value computed by the sorptivity model can reflect the experimental value to a large extent and, thus the sorptivity model can be applied to estimate the sorptivity of sandstone in the process of spontaneous imbibition.