Permeability describes the ability of material to transmit fluids or gases.
Shales have very low permeability. This means that once kerogen has developed it would require a lot of energy to move through the shale to be recovered. Once the shale has been subjected to high power microwaves several properties of shale and kerogen change to facilitate the recovery of the kerogen.
Increased permeability. Tests have shown that the permeability increases by several orders of magnitude because of the microwave radiation. The shale now has the permeability of coarse sand and allows the kerogn to flow though.
The kerogen becomes less viscous. Because of the high temperatures the kerogen flows much more freely though any medium.
Pressure gradient. The process of producing kerogen from oil shale also produces gases, which in turn push the kerogen towards the drill hole for fast recovery.
