Method for controlling the rheology of an aqueous fluid and gelling agent therefor

A method for controlling the rheology of fluid in an aqueous system comprising:

• a) providing one or more gelling agents selected from the group consisting of
• i) an amidoamine oxide of the general formula
• wherein R1 is a saturated or unsaturated, straight or branched chain aliphatic group of from about 7 to about 30 carbon atoms, R2 is a divalent alkaline group of from 2 to about 6 carbon atoms, R3 and R4 are the same or different and are alkyl or hydroxy alkyl of from 1 to about 4 carbon atoms, or R3 and R4 together with the nitrogen atom to which they are bonded form a heterocyclic ring of up to 6 members, and
• ii) a quaternary ammonium salt obtained from the reaction of a monoamine or diamine possessing at least one secondary or tertiary amine group with the amine nitrogen directly bonded to a saturated or unsaturated, straight or branched chain aliphatic group of from about 12 to about 30 carbon atoms and an aromatic dicarboxylic acid;
• b) adding said gelling agent to an aqueous fluid in an amount sufficient to form a viscoelastic fluid;
• and
• c) injecting said viscoelastic fluid into an underground formation.