Self-suspending proppants for hydraulic fracturing
The invention provides for modified proppants, comprising a proppant particle and a hydrogel coating, wherein the hydrogel coating localizes on the surface of the proppant particle to produce the modified proppant, methods of manufacturing such proppants and methods of use.
1. A process for fracturing a subterranean geological formation comprising introducing into said formation a treatment fluid wherein the fluid comprises a hydraulic fracturing fluid and a suspended modified proppant having hydrophilic properties while suspended during transport, wherein the suspended modified proppant comprises a proppant substrate particle and a swollen hydrogel coating,
wherein the hydrogel coating has been applied to a surface of the proppant substrate particle and localizes on the surface, and
wherein the process further comprises degrading the hydrogel coating by chemical, thermal, mechanical or biological means after the suspended modified proppant has been introduced into the formation.
2. The process of claim 1 , wherein degrading of the hydrogel coating is controlled by at least one of reaching a target temperature or amount of time in the fluid.
3. The process of claim 2 , wherein degrading of the hydrogel coating is controlled so as to direct placement of the proppant substrate particle of the modified proppant to a desired location within the formation.
4. The process of claim 1 , wherein degrading of the hydrogel coating is controlled so as to direct placement of the proppant substrate particle of the modified proppant to a desired location within the formation.
5. The process of claim 4 , wherein degrading of the hydrogel coating is accomplished by means of a chemical breaker.
6. The process of claim 4 , wherein degrading of the hydrogel coating is accomplished by means of an enzymatic breaker.
7. The process of claim 1 , wherein the suspended modified proppant has been formulated so that when 1 to 3 grams of the modified proppant in a dry state is added to 100 ml of tap water in a 100 ml graduated cylinder and then inverted 8 times, the modified proppant exhibits a settling time which is about 2 to about 7 times the settling time of the proppant substrate particle from which the modified proppant is made.
8. The process of claim 7 , wherein the modified proppant exhibits a settling time which is about 3 to about 7 times the settling time of the proppant substrate particle.
9. The process of claim 1 , wherein the modified proppant has been formulated so that, after 1 gram of the modified proppant is mixed with 10 g of tap water and allowed to settle, the modified proppant exhibits a settled bed height which is about 3 to about 28 times greater than the settled bed height of an otherwise identical proppant not modified with the hydrogel coating.
10. The process of claim 1 , wherein the hydrogel coating has been crosslinked.
11. The process of claim 10 , wherein the hydrogel coating has been crosslinked by means of a cross-linking agent which has been applied to the hydrogel coating subsequent to the application of the hydrogel coating to the proppant substrate particle.
12. The process of claim 10 , wherein the hydrogel coating has been crosslinked by means of a cross-linking agent, and further wherein the cross-linking agent is covalent and selected from an epoxide, an anhydride, an aldehyde, a diisocyanate and a carbodiamide.
13. The process of claim 12 , wherein the cross-linking agent is a diisocyanate.
14. The process of claim 10 , wherein the hydrogel coating has been crosslinked by an amount sufficient to prevent premature hydration due to humidity.
15. The process of claim 1 , wherein the hydrogel coating is formed from a hydrogel-forming polymer selected from polyacrylamide, copolymers of acrylamide with anionic and cationic comonomers, hydrolyzed polyacrylamide, copolymers of acrylamide with hydrophobic comonomers, poly(acrylic acid), poly(acrylic acid) salts, carboxymethyl cellulose, hydroxyethyl cellulose, hydroxypropyl cellulose, guar gum, alginate, carrageenan, locust bean gum, carboxymethyl guar, carboxymethyl hydroxypropyl guar gum, hydrophobically associating swellable emulsion (HASE) polymers, latex polymers and starches.
16. The process of claim 15 , wherein the hydrogel-forming polymer is selected from polyacrylamide, copolymers of acrylamide, poly(acrylic acid), poly(acrylic acid) salts and starches.
17. The process of claim 16 , wherein the hydrogel-forming polymer is a polyacrylamide.
18. The process of claim 1 , wherein the modified proppant comprises a cationic/anionic polymer pair.
19. The process of claim 18 , wherein the cationic polymer is a cationic polyacrylamide.
20. The process of claim 1 , wherein the hydrogel coating has a thickness between about 10% to about 1000% of the average diameter of the proppant substrate particle when suspended and a thickness between about 0.01% to about 20% of the average diameter of the proppant substrate particle before being suspended.
21. The process of claim 1 , wherein the hydrogel coating forms a substantially continuous film on the surface of the proppant substrate particle.
22. The process of claim 1 , wherein the proppant substrate particle comprises sand, bauxite, sintered bauxite or ceramic.
23. The process of claim 1 , wherein swelling of the hydrogel coating is essentially complete within about 10 minutes of being contacted with an excess of tap water at 20° C., and further wherein the modified proppant exhibits an expanded settled bed height which is substantially retained after having been subjected to shear at a shear rate of about 550 s −1 for 10 minutes.
24. The process of claim 23 , wherein after having been subjected to shear at a shear rate of about 550 s−1 for 10 minutes the expanded bed height of the modified proppant is at least about 75% of the settled bed height of the proppant before shearing begins.
25. The process of claim 1 , wherein swelling of the hydrogel coating is essentially complete within about 5 minutes of being contacted with an excess of tap water at 20° C.
26. The process of claim 1 , wherein the hydrogel coating on the proppant particle substrate includes an alcohol selected from ethylene glycol, propylene glycol and glycerol.