Method of treating a well with viscoelastic surfactant and viscosification activator

1. A method of fracturing a subterranean formation comprising introducing into the subterranean formation a fracturing fluid comprising a proppant suspended in a well treatment fluid, wherein the well treatment fluid comprises water or brine, a viscoelastic surfactant comprising a mixture of an anionic surfactant and a cationic surfactant and a viscosification activator, wherein the volumetric ratio of anionic surfactant to cationic surfactant is from about 1:4 to about 4:1 and further wherein the volumetric ratio of viscoelastic surfactant:viscosification activator is between from about 500:1 to about 1,000,000:1, the viscosity of the well treatment fluid being greater in the presence of the viscosification activator than in the absence of the viscosification activator.

2. The method of claim 1 , wherein the fluid contains the viscosification activator in an amount effective to initiate viscosification of the fluid at temperatures less than or equal to about 65° F.

3. The method of claim 1 , wherein the viscosification activator is selected from the group consisting of alkoxylated alcohols, condensation products of an alkyl phenol and an alkylene oxide, alkylene carbonates and glycol ethers.

4. The method of claim 3 , wherein the viscosification activator is propylene carbonate.

5. The method of claim 3 , wherein the viscosification activator is a linear or branched chain alkoxylated alcohol of the formula:

CH 3 (CH 2 ) n O(M-O) m —H

wherein n is from about 3 to about 22, m is from about 6 to about 40 and M is CH 2 —CH 2 , CH 2 —CH 2 —CH 2 , CH 2 —CH—CH 3 , CH 2 —CH 2 —CH 2 —CH 2 , CH 2 —CH—(CH 3 )—CH 2 or a mixture thereof.

6. The method of claim 5 , wherein n is from about 3 to 7 and m is from about 2 to about 5.

7. The method of claim 3 , wherein the viscosification activator is a glycol ether selected from the group consisting of ethylene glycol monobutyl ether, dipropylene glycol methyl ether, dimethyl glycol methyl ether, dipropylene glycol dimethyl ether and diethyleneglycol butyl ether.

8. The method of claim 7 , wherein the viscosification activator is ethylene glycol monobutyl ether.

9. The method of claim 1 , wherein the surfactant is a micellar assembly or vesicular assembly.

10. The method of claim 1 , wherein the ratio, by volume, of anionic surfactant to cationic surfactant is between from about 1:1 to about 1:1.95.

11. The method of claim 1 , wherein the well treatment fluid further comprises a gaseous foaming agent.

12. The method of claim 1 , wherein the anionic surfactant is sodium xylene sulfonate.

13. The method of claim 1 , wherein the cationic surfactant is N,N,N,trimethyl-1-octadecamonium chloride.

14. The method of claim 1 , further comprising an inorganic salt.

15. The method of claim 1 , wherein the volumetric ratio of viscoelastic surfactant:viscosification activator in the fluid is between from about 1,000:5 to about 750,000:1.

16. The method of claim 1 , wherein the treatment fluid further comprises a gaseous foaming agent.

17. The method of claim 1 , wherein the viscosification activator solubilizes the viscoelastic surfactant in the water or brine of the well treatment fluid.

18. A method of treating a well with a treatment fluid comprising (a) water or brine; (b) a viscoelastic surfactant comprising N,N,N,trimethyl-1-octadecamonium chloride and sodium xylene sulfonate; and (c) a viscosification activator selected from the group consisting of alkoxylated alcohols, condensation products of an alkyl phenol and an alkylene oxide, alkylene carbonates and glycol ethers, the method comprising introducing proppant suspended in the treatment fluid into the well, wherein the treatment fluid has a temperature less than or equal to 65° F. and further wherein the volumetric ratio of viscoelastic surfactant:viscosification activator in the treatment fluid is between from about 500:1 to about 1,000,000:1, the well treatment fluid does not contain a gaseous foaming agent, and the viscosification activator enhances the viscosification of the well treatment fluid transporting the proppant into the formation.

19. The method of claim 18 , wherein the viscosification activator is propylene carbonate.

20. The method of claim 18 , wherein the viscosification activator is a linear or branched chain alkoxylated alcohol of the formula:

CH 3 (CH 2 ) n O(M-O) m —H

wherein n is from about 3 to about 22, m is from about 6 to about 40 and M is CH 2 —CH 2 , CH 2 —CH 2 —CH 2 , CH 2 —CH—CH 3 , CH 2 —CH 2 —CH 2 —CH 2 , CH 2 —CH—(CH 3 )—CH 2 or a mixture thereof.

21. The method of claim 18 , wherein the viscosification activator is a glycol ether selected from the group consisting of ethylene glycol monobutyl ether, dipropylene glycol methyl ether, dimethyl glycol methyl ether, dipropylene glycol dimethyl ether and diethyleneglycol butyl ether.

22. A method of fracturing a formation comprising introducing into the formation a fracturing fluid comprising a proppant suspended in a well treatment fluid, wherein the well treatment fluid has a temperature less than or equal to 65° F. and wherein the well treatment fluid comprises water or brine; a viscoelastic surfactant comprising N,N,N,trimethyl-1-octadecamonium chloride and sodium xylene sulfonate and a viscosification activator, wherein the viscosification activator is present in the well treatment fluid in an amount effective to increase viscosification of the well treatment fluid and to transport the proppant into the formation, the volumetric ratio of viscoelastic surfactant:viscosification activator in the treatment fluid being between from about 500:1 to about 1,000,000:1 and wherein the viscosity of the well treatment fluid is greater in the presence of the viscosification activator than in the absence of the viscosification activator.

23. The method of claim 22 , wherein the well treatment fluid further comprises a gaseous foaming agent.

24. The method of claim 22 , wherein the viscosification activator is a linear or branched chain alkoxylated alcohol of the formula:

CH 3 (CH 2 ) n O(M-O) m —H

wherein n is from about 3 to about 22, m is from about 6 to about 40 and M is CH 2 —CH 2 , CH 2 —CH 2 —CH 2 , CH 2 —CH—CH 3 , CH 2 —CH 2 —CH 2 —CH 2 , CH 2 —CH—(CH 3 )—CH 2 or a mixture thereof.

25. The method of claim 22 , wherein the viscoelastic surfactant is a micellar assembly or vesicular assembly.