Process for reducing permeability in a subterranean formation

Abstract From the Canadian patent

A method is provided for blocking high permeability channels in subterranean geological formations using swelling clay. A slurry is prepared by mixing swelling clay such as bentonite, into an aqueous solution containing the salt of certain cations which inhibit clay swelling. The cations K~ Ca2~ and Mg2~, among others, are inhibitive of clay swelling. The clay slurry is introduced into a geological formation where it preferentialy enters channels of high permeability. There the slurry is contacted by NaCl brine solution present in natural or injected drive fluids and the inhibitive cations bound to the clay particles are replaced by Na~ ions which attract water molecules and promote clay …