Method of fracturing using mannanohydrolase enzyme breaker

1. A method of fracturing a subterranean formation comprising introducing into the formation an aqueous gellable fracturing fluid with a pH from 9.5 to 11.0 comprising:

(a) a hydratable polymer selected from the group consisting of guars and derivatized guars;

(b) a crosslinking agent for crosslinking the hydratable polymer to form a polymer gel; and

(c) an enzyme breaker comprising a mannanohydrolase enzyme that has an amino acid sequence that is at least 90% homologous to the amino acid sequence of SEQ ID NO:2.

2. The method of claim 1 , wherein the hydratable polymer is underivatized guar.

3. The method of claim 1 , wherein the crosslinking agent contains boron or is capable of providing boron ions to the fluid.

4. The method of claim 1 , wherein the downhole temperature of the subterranean formation is from 72° F. to 180° F.

5. The method of claim 1 , wherein the downhole temperature of the subterranean formation is in excess of 140° F.

6. The method of claim 1 , wherein the guar is selected from the group consisting of hydroxypropyl guar, carboxymethyl hydroxypropyl guar and carboxymethyl hydroxyethyl cellulose.

7. The method of claim 1 , wherein the crosslinking agent is a polymeric crosslinking agent containing a metal selected from the group consisting of aluminum, antimony, zirconium and titanium.

8. The method of claim 1 , wherein the hydratable polymer is in a solution selected from the group consisting of water, brine and water-alcohol mixtures.

9. The method of claim 1 , wherein the aqueous gellable fracturing fluid further comprises a pH regulating substance.

10. The method of claim 1 , wherein the aqueous gellable fracturing fluid is prepared on location.

11. The method of claim 1 , wherein the aqueous gellable fracturing fluid further contains a proppant.

12. The method of claim 1 , wherein the aqueous gellable fracturing fluid further contains at least one additive selected from the group consisting of surfactants, corrosion inhibitors, and crosslinking delaying agents.

13. A method of hydraulic fracturing a subterranean formation having a downhole temperature in excess of 160° F. comprises introducing into the formation at a pressure sufficient to create or enlarge fractures in the formation a fracturing fluid with a pH from 9.5 to 11.0 comprising:

(a) a hydratable polymer selected from the group consisting of underivatized guars and derivatized guars;

(b) a crosslinking agent for crosslinking the hydratable polymer to form a polymer gel; and

(c) an enzyme breaker comprising a mannanohydrolase enzyme that has an amino acid sequence that is at least 90% homologous to the amino acid sequence of SEQ ID NO:2.

14. The method of claim 13 , wherein the downhole temperature of the subterranean formation is in excess of 180° F.

15. The method of claim 13 , wherein the hydratable polymer is underivatized guar.

16. The method of claim 13 , wherein the crosslinking agent contains boron or is capable of providing boron ions to the fluid.

17. The method of claim 13 , wherein the guar is selected from the group consisting of hydroxypropyl guar, carboxymethyl hydroxypropyl guar and carboxymethyl hydroxyethyl cellulose.

18. The method of claim 13 , wherein the aqueous gellable fracturing fluid is prepared on location.

19. A method of fracturing a subterranean formation comprising introducing into the formation an aqueous gellable fracturing fluid with a pH from 9.5 to 11.0 comprising:

(a) an aqueous fluid selected from the group consisting of water, brine and water-alcohol mixtures;

(b) a hydratable polymer selected from the group consisting of underivatized guar, hydroxypropyl guar, carboxymethyl hydroxypropyl guar and carboxymethyl hydroxyethyl cellulose;

(c) a crosslinking agent for crosslinking the hydratable polymer to form a polymer gel, wherein the crosslinking agent contains boron or is capable of providing boron ions to the fluid; and

(d) an enzyme breaker comprising a mannanohydrolase enzyme that has an amino acid sequence that is at least 90% homologous to the amino acid sequence of SEQ ID NO:2.

20. The method of claim 19 , wherein the downhole temperature of the subterranean formation is from 72° F. to 180° F.