Method of using cationic polymers comprising imidazolium groups for permanent clay stabilization

A method of inhibiting the swelling of clay in subterranean formations at least comprising introducing a carrier fluid comprising at least one clay inhibitor into the formation, wherein at least one of the clay inhibitors is a cationic polymer comprising repeating units (I) selected from the group of

• wherein
• R1, R2, and R3 are each, independently of one another, H or a saturated or unsaturated, branched or unbranched, aliphatic and/or aromatic hydrocarbon moiety having from 1 to 20 carbon atoms which optionally may be substituted with functional groups,
• R4a, R4b, R4c are each, independently from one another, divalent, trivalent or tetravalent organic groups respectively comprising 2 to 50 carbon atoms, wherein the organic groups R4a, R4b, and R4c may optionally comprise functional groups and/or non-neighboring carbon atoms may be substituted by heteroatoms,
• Ym− are each, independently of one another, anionic counter ions, wherein m is an integer from 1 to 4,
• and wherein the cationic polymer has a weight average molecular weight Mw of at least 70,000 g/mol.