Hydraulic induces swelling of bentonite which can

lead it to extrude into near wellbore fractures, plugging

them and thus effectively reducing the permeability of the

near borehole damage zone. Here we present an

investigation of the length that the bentonite is able to

intrude a near borehole crack, showing the dependence of

this maximum intrusion length on the crack width and the

salinity of the hydrating fluid. From theory we predict two

limiting behaviors. For small widths we predict the

maximum length will increase proportionally to the width,

consistent with a balance of driving and resisting forces

associated with the intrusion. For large widths we predict

the intrusion length will decrease like the inverse of the

width, consistent with volume balance considerations.

Experiments performed in a cell analogous to a borehole

with a single rectangular crack (slot) confirm these

predictions. Furthermore, the observed reduction in the

intrusion length with increasing fluid salinity is shown to

be consistent with the reduced swelling potential of the

bentonite in more saline hydrating fluids.