The simulation showed filling rates for wells drilled into sandstone, shale, and limestone. Sandstone and shale are both composed of individual rock particles with pore spaces between the particles. Limestone can hold water only if cracks and cavities have been dissolved in the solid rock.
! Click each rock to see a photograph of that type of rock. Click again to see a visualization of water moving through the microscopic structure of the rock. Note that the scale of the microscopic images is not constant.