Proppants for hydraulic fracturing technologies
View Patent ↗The invention is directed to systems and methods for forming and using proppant particles having desirable attributes.
1. A method of fracturing a subterranean geological formation comprising introducing into said formation a treatment fluid wherein the fluid comprises an aqueous hydraulic fracturing fluid and suspended proppant particles having hydrophilic properties while suspended during transport, wherein the suspended proppant particles comprise:
a proppant particulate substrate,
an inner polymeric layer made from a first polymeric material deposited on the particulate substrate, and
a distended hydrophilic outer coating layer made from a second polymeric material deposited upon the first layer, wherein the distended hydrophilic outer coating layer comprises a hydrophilic polymer selected from the group consisting of EO/PO copolymers, polyvinyl acetate, polyethylene-co-vinyl acetate, polyvinyl alcohol, polysaccharides and combinations thereof, wherein the second polymeric material is selected so that
(a) when this outer coating layer is exposed to the aqueous fracturing fluid, it distends and imparts hydrophilic properties to the suspended proppant particles, and
(b) the outer coating layer protects the inner polymeric layer from the fluid in the fracture.
2. The method of claim 1 , wherein the inner polymeric layer comprises a pressure sensitive polymeric adhesive.
3. The method of claim 1 , wherein the first polymeric material comprises a hydrophobic polymer.
4. The method of claim 1 , wherein the outer coating layer is affixed to the inner polymeric layer.
5. The method of claim 4 , wherein the outer coating layer is affixed to the inner polymeric layer by swelling-deswelling.
6. The method of claim 1 , wherein the proppant particulate substrate comprises sand.
7. The method of claim 1 , wherein the proppant particulate substrate comprises ceramic.
8. The method of claim 1 , wherein the proppant particulate substrate has a specific gravity from about 1.0 to about 2.7 g/cc.
9. The method of claim 1 , wherein the proppant particulate substrate comprises a material having lower density than sand.
10. The method of claim 1 , wherein the inner polymeric layer is deposited on the proppant particulate substrate by solution coating.
11. The method of claim 1 , wherein the inner polymeric layer is deposited on the proppant substrate particle by in-situ coating.
12. The method of claim 1 , wherein the inner polymeric layer comprises a polymer selected from the group consisting of phenolic resins, epoxy resins, furan resins, phenolic formaldehyde resins, melamine formaldehyde resins, urethane resins, phenolic/ furan resin mixtures, urea-aldehyde resins, furan/furfuryl alcohol resins, phenolic/latex resins, polyester resins, acrylate resins, and combinations thereof.
13. The method of claim 1 , wherein the outer coating layer comprises a block copolymer having hydrophilic and hydrophobic sections.
14. The method of claim 1 , wherein the outer coating layer is produced by chemical modification of the inner layer or an intermediate layer.
15. The method of claim 1 , further comprising a low density layer external to the outer coating layer.
16. The method of claim 15 , wherein the low density layer comprises a foam.
17. The method of claim 1 , wherein when the suspended proppant particles reach their destination within the subterranean geological formation, the distended hydrophilic outer coating layer rearranges itself to expose the inner polymeric layer, thereby enabling multiple composite proppant particles to fix themselves to one another.
18. The method of claim 1 , wherein the outer polymer coating remains substantially intact until the suspended proppant particles have been conveyed to their destinations in the subterranean formation.
19. The method of claim 1 wherein the hydrophilic outer layer creates a water-like layer on the surface of the particle, making it slippery and one of reducing friction between particles or reducing drag against water.