Abstract
Fluid in porous media flows through tortuous paths. If the size of the solid particles suspended in the fluid and the fluid velocities are large enough, Brownian motion effects may not be dominant. In this parameter regime, the average velocity of the particles is different than that of the fluid. We obtain the relation between the average velocity of the particles and the average velocity of the fluid in the context of a simple mathematical model and we apply our results to flows near wells.