Patent ID: 8785355

Claim:
An aqueous wellbore fluid comprising an anionic viscoelastic surfactant of formula I: R—X—(CR 5 R 6 ) m —SO 3 −B + (I) in which: R is a saturated or unsaturated, linear or branched aliphatic hydrocarbon chain comprising from 15 to 22 carbon atoms, including mixtures thereof and/or optionally incorporating an aryl group; X is —(C═O)N(R 7 )—or —N(R 7 )(C═O)—; R 5 and R 6 are the same or different and are each independently hydrogen, a linear saturated aliphatic hydrocarbon chain of at least 1 carbon atom, a branched saturated aliphatic hydrocarbon chain of at least 2 carbon atoms, or a linear saturated aliphatic hydrocarbon chain of at least 1carbon atom or a branched aliphatic hydrocarbon chain of at least 2 carbon atoms with one or more of the hydrogen atoms replaced by a hydroxyl group; or when X is —N(R 7 )(C═O)—, the group (CR 5 R 6 ) may include a COO − group; R 7 is a hydrogen, a linear saturated aliphatic hydrocarbon chain of at least 1 carbon atom, a branched saturated aliphatic hydrocarbon chain of at least 2 carbon atoms, a linear saturated aliphatic hydrocarbon chain of at least 1 carbon atom or a branched saturated aliphatic hydrocarbon chain of at least 2 carbon atoms with one or more of the hydrogen atoms replaced by a hydroxyl group, or a cyclic hydrocarbon group; B + is hydrogen or a monovalent cation and m is an integer of from 1 to 4; in the form of monomeric unit, a dimer or oligomer; the amount of the anionic viscoelastic surfactant which is present in the wellbore fluid being sufficient that the fluid is an aqueous viscoelastic gel.