“…Numerous experimental studies have shown either an early breakthrough of particles , or a significant delay. , Yang and Bedrikovetsky introduced a drift delay factor α in order to characterize the velocity difference between particles and fluid. “Faster” particle migration, i.e., α > 1, is explained by the division of porous space into fractions that are accessible and inaccessible to finite-size (nonzero) particles. , While “slower” particle movement, i.e., α < 1, is attributed to the tortuosity of pores, the rolling or sliding of particles near the rock surface is where the velocity is lower compared with the average fluid velocity. , …”