Self-suspending proppants for hydraulic fracturing
View Patent ↗The present invention provides modified proppants, and methods for their manufacture. In embodiments, the modified proppant comprises a proppant particle and a hydrogel coating, wherein the hydrogel coating is applied to a surface of the proppant particle and localizes on the surface to produce the modified proppant. In embodiments, formulations are disclosed comprising the modified particles, and methods are disclosed for using the formulations.
1. A modified proppant for propping open a fracture in a geological formation, the modified proppant comprising a proppant particle substrate and a coating of a hydrogel-forming polymer, wherein the coating localizes on the surfaces of the proppant particle substrate to produce the modified proppant, wherein the coating comprises a hydrogel-forming polymer which forms a substantially continuous film on the surface of the proppant particle which is crosslinked, wherein the hydrogel-forming polymer is selected so that when 1 to 3 grams of the dried modified proppant 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, and wherein the coating has been formulated to prevent premature release of the coating so that the modified proppant can be directed to a desired target location in the fracture.
2. The modified proppant of claim 1 , wherein the modified proppant exhibits a settling time which is about 3 to about 7 times the settling time of the proppant substrate particle.
3. The modified proppant of claim 1 , wherein the hydrogel-forming polymer is selected 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 (2.7/0.8) to about 28 (22.6/0.8) times greater than the settled bed height of an otherwise identical proppant not modified with a hydrogel coating.
4. The modified proppant of claim 1 , wherein the hydrogel-forming polymer has been crosslinked by means of a subsequently applied cross-linking agent.
5. The modified proppant of claim 4 , wherein the cross-linking agent is covalent and selected from an epoxide, an anhydride, an aldehyde, a diisocyanate and a carbodiamide.
6. The modified proppant of claim 5 , wherein the cross-linking agent is a diisocyanate.
7. The modified proppant of claim 1 , wherein the coating has been crosslinked by a covalent crosslinking agent selected from an epoxide, an anhydride, an aldehyde, a diisocyanate and a carbodiamide.
8. The modified proppant of claim 7 , wherein the cross-linking agent is a diisocyanate.
9. The modified proppant of claim 1 , wherein the hydrogel-forming polymer has been crosslinked by an amount sufficient to prevent premature hydration due to humidity.
10. The modified proppant of claim 1 , wherein the hydrogel-forming polymer is 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.
11. The modified proppant of claim 10 , wherein the hydrogel-forming polymer is selected from polyacrylamide, copolymers of acrylamide, poly(acrylic acid), poly(acrylic acid) salts and starches.
12. The modified proppant of claim 11 , wherein the hydrogel-forming polymer comprises a polyacrylamide.
13. The modified proppant of claim 1 , wherein the modified proppant comprises a cationic/anionic polymer pair.
14. The modified proppant of claim 13 , wherein the cationic/anionic polymer pair comprises a cationic polymer and an anionic polymer.
15. The modified proppant of claim 14 , wherein the cationic polymer is a cationic polyacrylamide.
16. The modified proppant 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.
17. The modified proppant of claim 16 , 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.
18. The modified proppant of claim 16 , 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 20 minutes.
19. The modified proppant of claim 16 , wherein after having been subjected to shear at a shear rate of about 550 s −1 for 20 minutes the expanded bed height of the modified proppant is at least about 50% of the settled bed height of the proppant before shearing begins.
20. The modified proppant 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.
21. The modified proppant of claim 1 , wherein the hydrogel coating on the proppant particle substrate includes an alcohol.
22. The modified proppant of claim 21 , wherein the alcohol is at least one of ethanol, propanol, ethylene glycol, propylene glycol and glycerol.
23. The modified proppant of claim 22 , wherein the alcohol is at least one of ethylene glycol, propylene glycol and glycerol.
24. A method of fracturing a geological formation comprising introducing into the well a hydraulic fracturing formulation comprising a water-based fracturing fluid and a proppant, wherein the proppant comprises the modified proppant of claim 1 .
25. The method of claim 24 , wherein after the modified proppant has been introduced into the well and become distended from exposure to the water-based fracturing fluid, the method further comprises causing the swollen hydrogel polymer to be degraded by chemical, thermal, mechanical or biological mechanisms.
26. The method of claim 25 , wherein degradation of the swollen hydrogel polymer is controlled to direct the placement of the modified proppant to a desired location in the fracture.
27. The method of claim 26 , wherein the swollen hydrogel polymer is degraded by means of a chemical breaker.