Numerical simulations of radon diffusion-seepage in single fracture of rock

The joint roughness coefficient (JRC) of rock fractures significantly effects their seepage characteristics, which is critical in radon diffusion-seepage studies. It is worthwhile to investigate how to accurately characterize the rock fracture roughness and its effect on radon diffusion-seepage patterns within fractured porous media. In this study, the roughness of single-fracture rock is thoroughly considered and described by the Barton curve. Furthermore, this study examines the effects of pressure gradient, temperature, and water saturation on radon diffusion-seepage in fracture-containing porous media. Additionally, this study investigates the variation in seepage velocity within cracks under various pressure gradients, and further analyze the impact of roughness on radon exhalation rate in rocks. The results indicate that: (1) the JRC significantly influences the diffusion-seepage of radon in rocks. The radon exhalation rate on the low-pressure side and the seepage velocity within the fracture increase approximately by 30% and 10%, respectively. (2) The radon exhalation rate on the low-pressure side of the rock correlates positively with the JRC, whereas the radon exhalation rate in the fracture shows a negative correlation with the JRC. Concurrently, the pressure gradient, temperature and water saturation also significantly impact the radon exhalation rate. (3) The seepage velocity within the fracture increases with the rise of osmotic pressure in a fixed JRC value. AS the increase of JRC, the seepage velocity of the rock fracture decreases by approximately 7.9%–10.8%.