A reservoir rock can store fluids because the reservoir has pore space. That's the spaces between the grains making up the rock, like marbles packed into a jar, we can still add water to the jar full of marbles. So what if we change out the marbles for golf balls or grains of sand? While we get more or less number of pores, do we get more pore volume (open space)? I say that as we decrease the grain size, getting more smaller pores, we get more pore volume (can hold more fluid). Prove me wrong, or correct. Note; fluids can be water, crude oil, or gas.