SELF-SUSPENDING PROPPANTS MADE FROM POWDERED HYDROGEL-FORMING POLYMERS

1 . A self-suspending proppant comprising a proppant particle substrate, a binder on the surface(s) of the proppant particle substrate, and a layer of a powder of a hydrogel-forming polymer bound to the surface(s) of the proppant particle substrate by the binder, wherein the self-suspending proppant further comprises a crosslinked shell.

2 . The self-suspending proppant of claim 1 , wherein the hydrogel-forming polymer is an acrylamide polymer.

3 . The self-suspending proppant of claim 1 , wherein the hydrogel-forming polymer is poly(acrylamide-co-sodium acrylate).

4 . The self-suspending proppant of claim 1 , wherein the hydrogel-forming polymer has a particle size of 12-140 mesh.

5 . The self-suspending proppant of claim 1 , wherein the crosslinked shell is produced by adding a covalent crosslinking agent.

6 . The self-suspending proppant of claim 5 , wherein the crosslinking agent is a diisocyanate.

7 . The self-suspending proppant of claim 6 , wherein the diisocyanate is p-MDI.

8 . The self-suspending proppant of claim 1 , wherein the self-suspending proppant exhibits (a) a volumetric expansion as determined by the Settled Bed Height Analytical test described in the specification of ≥1.5, (b) storage stability as reflected by the fact that it remains free flowing after having been subjected to a relative humidity of about 80%-90% for one hour at 25-35° C., and (c) a durability of ≥1.5 as determined by the Shear Analytical Test described in the specification.

9 . The self-suspending proppant of claim 8 , wherein the hydrogel-forming polymer is an acrylamide polymer and further wherein the crosslinked shell is produced by adding a covalent crosslinking agent.

10 . The self-suspending proppant of claim 9 , wherein the hydrogel-forming polymer is a copolymer of acrylamide and acrylic acid or an alkali metal acrylic acid salt and further wherein the crosslinking agent is a diisocyanate.

11 . A process for improving the durability of a self-suspending proppant comprising a proppant particle substrate, a binder on the surface(s) of the proppant particle substrate, and a layer of a hydrogel-forming polymer in form of powder particles bound to the surface(s) of the proppant particle substrate by the binder, the process comprising applying a crosslinking agent capable of crosslinking the hydrogel-forming polymer to these powder particles after they have been contacted with the binder.

12 . The process of claim 11 , wherein the hydrogel-forming polymer is an acrylamide polymer.

13 . The process of claim 11 , wherein the hydrogel-forming polymer is poly(acrylamide-co-sodium acrylate).

14 . The process of claim 11 , wherein the hydrogel-forming polymer has a particle size of 12-140 mesh.

15 . The process of claim 11 , wherein the crosslinking agent is covalent.

16 . The process of claim 15 , wherein the crosslinking agent is a diisocyanate.

17 . The process of claim 16 , wherein the diisocyanate is p-MIDI.

18 . A process for improving the durability of a self-suspending proppant comprising a proppant particle substrate, a binder on the surface(s) of the proppant particle substrate, and a layer of powdered hydrogel-forming polymer on the binder, wherein the powdered hydrogel-forming polymer is contacted with the binder by adding the powdered hydrogel-forming polymer to a mixture of the proppant particle substrate and the binder, the process comprising applying a crosslinking agent capable of crosslinking the hydrogel-forming polymer to the mixture of the proppant particle substrate and the binder after the powdered hydrogel-forming polymer is added to this mixture.

19 . The process of claim 18 , wherein the hydrogel-forming polymer is an acrylamide polymer.

20 . The process of claim 11 , wherein the crosslinking agent is covalent.

21 . The process of claim 20 , wherein the crosslinking agent is a diisocyanate.