Patent ID: 7514392

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, in which at least one of the amine functional groups have been reacted with a predetermined amount of C1 to C25 carboxylic acid; and wherein the concentration of shale hydration inhibition agent is from about 0.5 to about 20 pounds per barrel of the water base well bore fluid.