Actual absorption is a little different if the sand is allowed to drain. When wet sand is allowed to drained it will loose a few percent of it's water but most will still cling to the particles. I explain how I did my tests on the page. That should get you started in your investigation. Very fine particles leave very little room for fluid to move through.
Oil moving through sand is also just like sand moving through oil.
The forces depend on the weights, pressure and space available. You can predict how fast things will move through fluids with such as this work on sand settling through water. But the real forces and particle sizes will likely be different in nature. The best way to test such effects is to measure them. The main ingredient is silica for all glass.