Patent ID: 7494958

Claim:
A water-base well bore fluid for use in a subterranean well penetrating through one or more subterranean formations containing a shale which swells in the presence of water, wherein the fluid comprises: an aqueous based continuous phase; a weighting agent; and a shale hydration inhibition agent having the formula: in which R and R'independently selected from hydrogen, methyl, ethyl or propyl, R′is a bridging group having 1 to 20 carbon atoms and n has a value from 1 to 4 and X is an amine, hydroxyl, alkoxy, carboxy group; wherein the shale hydration inhibition agent is a mixture of aminoalkylcyclohexylamines and aminoarylcyclohexlamines and wherein the shale hydration inhibition agent is present in sufficient concentration to reduce the swelling of shale.