Sorry I tried to answer the original question
There should be little if any fluid loss into shale. Otherwise slates would not be much use on a roof. If you run a log you should not see a filter cake against a shale formation.
What does occur is a type of osmosis called pore pressure penetration. As we are drilling over balanced the excessive hydrostatic will act as a driving force pushing ions into the formations and increasing the near well bore pressure. The drilled formations will increase in pressure due to PPP and there will be no overbalance allowing shales to fail with drill pipe movement. At the same time K+ ions will be push into the shale pores.
K+ ions can reduce shale swelling leading (they may also increase permeability) by increasing shale strength in certain clay formations such as smectite and illite.
But Inhibitive fluids can also promote pressure invasion and borehole instability.
So there are two opposing forces the inhibition from K+ and PPP lead to absence of an overbalance.
Field and laboratory experience suggest that the benefit of inhibition (K+) outweighs the drawback of pressure invasion. However, PPP does suggest that open hole time should be limited with K+ based systems otherwise as there is no effective overbalance borehole instability can occur resulting in cavings and the loss of many long deviated shale sections drilled with KCl systems.