Method of fracturing subterranean formations with crosslinked fluid
View Patent ↗Subterranean formations are subjected to hydraulic fracturing with an aqueous fracturing fluid having guar or a derivative thereof, a borate crosslinking agent and proppant. The fracturing fluid is prepared in a blender and then pumped into the wellbore through an entrance site. The apparent viscosity of the fluid decreases distally from the entrance site such that (i) the apparent viscosity of the fracturing fluid 100 feet from the entrance site is less than 10 percent of the apparent viscosity of the fracturing fluid at the entrance site; (ii) the apparent viscosity of the fracturing fluid 15 minutes after introduction into the entrance site is less than 15% of the apparent viscosity of the fracturing fluid at the entrance site; or (iii) the apparent viscosity of the fracturing fluid is less than 10 cP within 15 minutes after being introduced through the entrance site.
1. A method of fracturing a subterranean formation penetrated by a wellbore, comprising the steps of:
formulating a viscous fracturing fluid comprising (i) water, (ii) a hydratable polymer selected from the group consisting of guar and guar derivatives, (iii) a borate based crosslinking agent and (iv) a proppant, wherein the hydratable polymer loading in the viscous fracturing fluid is from 6 to 18 pptg;
pumping the viscous fracturing fluid through an entrance site in the wellbore into the reservoir; and propagating fractures within the reservoir while decreasing the viscosity of the viscous fracturing fluid distally from the entrance site wherein at least one of the following conditions prevail at in situ conditions during propagation of the fractures:
(a) the apparent viscosity of the fracturing fluid 100 feet from the entrance site is less than 10 percent of the apparent viscosity of the fracturing fluid at the entrance site;
(b) the apparent viscosity of the fracturing fluid 15 minutes after introduction into the entrance site is less than 15% of the apparent viscosity of the fracturing fluid at the entrance site; or
(c) the apparent viscosity of the fracturing fluid is less than 10 cP within 15 minutes after being introduced through the entrance site.
2. The method of claim 1 , wherein the hydratable polymer loading in the fracturing fluid is from about 8 to about 12 pptg.
3. The method of claim 2 , wherein the hydratable polymer loading in the fracturing fluid is from about 6 to about 10 pptg.
4. The method of claim 1 , wherein the hydratable polymer is selected from the group consisting of guar gum, hydroxypropyl guar, carboxymethyl hydroxypropyl guar and carboxymethyl hydroxyethyl guar and mixtures thereof.
5. The method of claim 1 , wherein the hydratable polymer is underivatized guar.
6. The method of claim 1 , wherein the borate based crosslinking agent contains borate or generates borate.
7. The method of claim 6 , wherein the borate based crosslinking agent is a borate ion donating material.
8. The method of claim 6 , wherein the borate based crosslinking agent is selected from the group consisting of organo-borates, mono-borates, poly-borates and mineral borates.
9. A method of fracturing a subterranean formation penetrated by a wellbore, comprising:
(a) pumping an aqueous fracturing fluid into the wellhead of the wellbore and through an entrance site in the wellbore into the reservoir, wherein the aqueous fracturing fluid comprises a hydratable polymer, a borate based crosslinking agent and proppant, wherein the hydratable polymer loading in the fracturing fluid is from 6 to 18 pptg;
(b) propagating fractures within the formation; and
(c) decreasing the apparent viscosity of the fluid distally from the entrance site during propagation of the fractures such that at least one of the following conditions prevails:
(i) the apparent viscosity of the fracturing fluid 100 feet from the entrance site is less than 10 percent of the apparent viscosity of the fracturing fluid at the entrance site;
(ii) the apparent viscosity of the fracturing fluid 15 minutes after introduction into the entrance site is less than 15% of the apparent viscosity of the fracturing fluid at the entrance site; or
(iii) the apparent viscosity of the fracturing fluid is less than 10 cP within 15 minutes after being introduced through the entrance site.
10. The method of claim 9 , wherein the hydratable polymer loading in the fracturing fluid is from about 8 to about 12 pptg.
11. The method of claim 10 , wherein the hydratable polymer loading in the fracturing fluid is from about 6 to about 10 pptg.
12. The method of claim 9 , wherein the hydratable polymer is selected from the group consisting of guar gum, hydroxypropyl guar, carboxymethyl hydroxypropyl guar and carboxymethyl hydroxyethyl guar and mixtures thereof.
13. The method of claim 9 , wherein the hydratable polymer is underivatized guar.
14. The method of claim 9 , wherein the borate based crosslinking agent contains borate or generates borate.
15. The method of claim 14 , wherein the borate based crosslinking agent is a borate ion donating material.
16. The method of claim 14 , wherein the borate based crosslinking agent is selected from the group consisting of organo-borates, mono-borates, poly-borates and mineral borates.
17. The method of claim 9 , wherein the apparent viscosity of the fracturing fluid 100 feet from the entrance site is less than 10 percent of the apparent viscosity of the fracturing fluid at the entrance site.
18. The method of claim 17 , wherein the apparent viscosity of the fracturing fluid 100 feet from the entrance site is less than 5 percent of the viscosity of the fracturing fluid at the entrance site.
19. The method of claim 18 , wherein the apparent viscosity of the fluid 200 feet from the entrance site is less than 1 percent of the viscosity of the fracturing fluid at the entrance site.
20. The method of claim 9 , wherein the subterranean formation is shale.
21. The method of claim 9 , wherein the subterranean formation is a tight gas formation.
22. The method of claim 9 , wherein the hydratable polymer, in the aqueous fluid, has an intrinsic viscosity greater than about 14 dL/g.
23. The method of claim 9 , wherein the fracturing fluid further contains a buffering agent effective to provide a pH for the fluid in the range from about 9.5 to 11.5.
24. The method of claim 9 , wherein the apparent viscosity of the fracturing fluid 15 minutes after introduction into the entrance site is less than 15% of the apparent viscosity of the fracturing fluid at the entrance site.
25. The method of claim 24 , wherein the apparent viscosity of the fracturing fluid 15 minutes after introduction into the entrance site is less than 10% of the apparent viscosity of the fracturing fluid at the entrance site.
26. The method of claim 25 , wherein the apparent viscosity of the fracturing fluid 30 minutes after introduction into the entrance site is less than 5% of the apparent viscosity of the fracturing fluid at the entrance site.
27. The method of claim 9 , wherein the apparent viscosity of the fracturing fluid is less than 10 cP within 15 minutes after being introduced through the entrance site.
28. The method of claim 27 , wherein the apparent viscosity of the fracturing fluid is less than 5 cP within 15 minutes after being introduced through the entrance site.
29. The method of claim 28 , wherein the apparent viscosity of the fracturing fluid is less than 3 cP within 30 minutes after being introduced through the entrance site.
30. The method of claim 9 , wherein the aqueous fluid, when pumped into the wellhead, has a viscosity from about 10 to about 120 cP.
31. A method of fracturing a subterranean formation penetrated by a wellbore, wherein the permeability of the subterranean formation is between from about 10 nanodarcies to about 1.0 mD, the method comprising:
(a) forming a viscous fracturing fluid comprising water, a viscosifying polymer selected from the group consisting of guar and guar derivatives, a borate based crosslinking agent and proppant, wherein the viscous fracturing fluid has a viscosity between from about 10 to about 120 cP at a temperature range between from about 80° F. to about 125° F. and wherein the guar or guar derivative loading in the fracturing fluid is from 8 to 12 pptg;
(a) pumping the viscous fracturing fluid into the wellhead of the wellbore while minimizing settling of proppant from the fluid during the pumping;
(c) transporting the viscous fracturing fluid through an entrance site in the wellbore;
(d) propagating fractures in the formation; and
(e) decreasing the viscosity of the viscous fracturing fluid upon the fluid entering the entrance site such that at least one of the following conditions prevail:
(i) the apparent viscosity of the fracturing fluid 100 feet from the entrance site is less than 10 percent of the apparent viscosity of the fracturing fluid at the entrance site;
(ii) the apparent viscosity of the fracturing fluid 15 minutes after introduction into the entrance site is less than 15% of the apparent viscosity of the fracturing fluid at the entrance site; or
(iii) the apparent viscosity of the fracturing fluid is less than 10 cP within 15 minutes after being introduced through the entrance site.