Patent EA-004093-B1 (EA)
Title: Viscosity reduction of viscoelastic surfactant based fluids
Inventor: NELSON ERIC B
IPC: C09K8/536
Filed: 2001-04-03
Abstract: 1. A composition for treating a subterranean formation comprising an aqueous fluid comprising a thickening amount of a viscoelastic surfactant and a precursor of a breaking system that causes a reduction in viscosity of the fluid. 2. The composition of claim 1, wherein the precursor of the breaking system is selected among at least one of the following salts: ammonium persulfate, potassium chloride, sodium hexafluorophosphate and sodium salicylate and wherein said salts are provided under an encapsulated form. 3. The composition of claim 1, wherein the precursor of the breaking system comprises resin-coated proppant. 4. The composition of claim 1, wherein the precursor of the breaker system comprises at least of one of the following: an ester, a carboxylate anion, organic sulfate based salts, in particular, alkyl and ether sulfates, alkylhalogenide, alkylphosphate, arylphosphate and mixture thereof. 5. The composition of claim 4, wherein said precursor of the breaking agent is C18-C20 alkylsulfate and mixture thereof. 6. The composition of claim 1, wherein the precursor of the breaking system comprises at least one of the following: a C12-C18 alcohol, alkyl amines, in particular, dodecyle amines, alkanes, alkenes, aromatics and mixtures thereof. 7. The composition of claim 1, wherein the viscoelastic surfactant is anionic and/or cationic and the precursor of the breaking system is a slow-soluble surfactant having hydrophilic headgroups oppositely charged to the hydrophilic headgroups of the anionic or cationic surfactants of the viscoelastic surfactant fluid. 8. The composition of claim 1, wherein the precursor of the breaker system is provided in the form of nanoparticles. 9.The composition of claim 1, wherein the breaker system comprises alcohol, in particular, methanol or ethanol. 10. The composition according to any of proceeding claims, wherein the cationic viscoelastic surfactant is erucyl methyl bis (2-hydroxyethyl) ammonium chloride. 11. A composition for treating a subterranean formation comprising an aqueous fluid comprising a thickening amount of a zwitterionic surfactant and citric acid. 12. A method of treating a subterranean formation by injecting down a well a composition according to any of claims 1-11, that causes a reduction in viscosity of the fluid after its injection but does not significantly impact its viscosity at surface and during the injection. 13. The method of claim12 comprising providing a precursor that releases a breaking system by at least one of the following process: melting, slow dissolution, reaction with a compound present in the fluid or added to the fluid during or after the step of injecting, rupture of an encapsulating coating and de-adsorption of a breaking agent absorbed into solid particles. 14. The method of claim 12, wherein the breaker system comprises a carboxylic acid released from a precursor comprising a carboxylate anion, said released being performed after lowering of the pH of the viscoelastic surfactant fluid through hydrolysis of an ester. 15. The method of claim 12, wherein the breaking system reduces low shear viscosity. 16. The method of claim 15, wherein the breaking system does not substantially reduce high shear viscosity. 17. The method of any of claims 12-16, wherein the breaking system is added to the viscoelastic fluid during the pad or the pre-pad stage. 18. The method of any of claims 12-16, wherein said treatment consists of at least one of the following: gravel packing, hydraulic fracturing, acid fracturing and acidizing. 19. A method of treating a subterranean formation by first injecting, down a well, a solid-free aqueous fluid comprising a thickening amount of a cationic viscoelastic surfactant and an alcohol, selected among methanol and alcohol, and then, a proppant-containing aqueous fluid comprising a thickening amount of said cationic viscoelastic surfactant.