Modelling of mass transport in fractured crystalline rock using velocity interpolation and cell-jump particle tracking methods

Abstract

In this study, two particle tracking methods, velocity interpolation, and cell-jump, were employed to simulate tracer transport in fractured crystalline rock. The models, belonging to DECOVALEX-2023 Task F1, included one considering only the influence of deterministic (major) fractures, and another considering both deterministic and stochastic (background) fractures. The simulations involved converting fracture properties into equivalent hydraulic parameters for each three-dimensional grid, simulating steady-state flow fields, and evaluating transport parameters using particle tracking methods. Using transport parameters, one-dimensional transport pathways were simulated for evaluating mass transport of tracers considering non-reactive, decay, and adsorption. Moment analysis was then utilized to quantify breakthrough curves and compare the performance of the two particle tracking methods. The conclusion is that the cell-jump method, despite facing issues with numerical dispersion that results in a broader distribution of particle trajectories, demonstrates advantages in providing relative shorter mean breakthrough times and less temporal spreading compared to the velocity interpolation (VI) method in cases involving stochastic background fractures. Both methods are limited by the issue of particles entering the matrix due to the application of non-zero permeability for numerical convenience.