Consolidated proppants having high mechanical strength and process for the preparation thereof

1. A process for the preparation of a consolidated proppant, which process comprises

(a) mixing a consolidating agent with a proppant; and

(b) curing the consolidating agent mixed with the proppant at elevated pressure and elevated temperature;

the consolidating agent comprising

(A1) a hydrolysate or condensate of

(i) at least one functionalized organosilane of formula (I)

(R x ) b R c SiX 4−b−c   (I)

in which the radicals Rx are identical or different and represent groups which cannot be eliminated hydrolytically and comprise at least one crosslinkable functional group, the radicals R are identical or different and represent groups which cannot be eliminated hydrolytically, the radicals X are identical or different and represent groups which can be eliminated hydrolytically or hydroxyl groups, b is 1, 2 or 3, c is 0, 1 or 2, (b+c) being 1, 2 or 3;

(ii) optionally, at least one hydrolyzable silane of formula (II)

SiX 4   (II)

in which X is as defined in formula (I); and

(iii) at least one metal compound of formula (III)

MX a   (III)

in which M is a metal of main groups I to VIII or of subgroups II to VIII of the Periodic Table of Elements, including boron, X is as defined in formula (I), it being possible for two groups X to be replaced by an oxo group, and a corresponds to the valency of M;

a molar ratio of silicon compounds used to metal compounds used being from 10,000:1 to 10:1, and

(A2) an organic crosslinking agent having at least two functional groups.

2. The process of claim 1 , wherein M in formula (III) is selected from B, Al, Zr, or Ti.

3. The process of claim 2 , wherein M in formula (III) comprises Ti.

4. The process of claim 1 , wherein before and/or during curing a liquid or gaseous medium is passed through and mixed with the proppant to be consolidated to adjust a porosity.

5. The process of claim 4 , wherein the liquid or gaseous medium comprises air.

6. The process of claim 4 , wherein the liquid or gaseous medium is loaded with volatile, gaseous or vaporizable acids, bases or other catalysts.

7. A consolidated proppant, wherein the proppant has hydrolytic stability under hydrothermal conditions and is obtainable by the process of claim 1 .

8. The consolidated proppant of claim 7 , wherein the proppant is porous.

9. The consolidated proppant of claim 7 , wherein the proppant has a degree of porosity of from 5% to 50%.

10. The process of claim 1 , wherein (A1) is formed by hydrolysis or condensation of

(i) at least one functionalized organosilane of formula (I)

(iv) at least one organosilane of formula (Ia)

R n SiX 4−n   (Ia)

in which the radicals R are identical or different and represent groups which cannot be eliminated hydrolytically, the radicals X are identical or different and represent groups which can be eliminated hydrolytically or hydroxyl groups and n is 1, 2 or 3,

(ii) at least one hydrolyzable silane of formula (II), and

(iii) at least one metal compound of formula (III);

a molar ratio of silicon compounds used to metal compounds used being from 10,000:1 to 10:1.

11. The process of claim 1 , wherein a weight ratio of a sum of silicon compounds and metal compounds used for making (A1) to (A2) is from 1:5 to 1:0.3.

12. The process of claim 1 , wherein a molar ratio of functional groups of the functionalized organosilane to functional groups of (A2) is from 10:1 to 1:2.

13. The process of claim 1 , wherein functional groups of the functionalized organosilane and of (A2) comprise one or more groups selected from vinyl, acryloyl or methacryloyl groups.

14. The process of claim 1 , wherein (A2) comprises one or more of a di-or polyfunctional acrylate or methacrylate, an unsaturated polyester or an epoxy resin.

15. The process of claim 1 , wherein the consolidating agent comprises a thermal catalyst.

16. The process of claim 1 , wherein the consolidating agent is cured at a temperature of at least 40° C. and a pressure of at least 8 bar.

17. The process of claim 1 , wherein the proppant is consolidated after it has been placed in a fracture by subsequent injection of the consolidating agent and subsequent curing.

18. The process of claim 1 , wherein the consolidating agent comprises a hydrolysate or precondensate of (i) a vinyl-, acryloyl- or methacryloylsilane, (iv) an alkylsilane, (ii) an orthosilicic acid ester and (iii) a metal alkoxylate.

19. The process of claim 1 , wherein the consolidating agent is prepared by a sol-gel process using a substoichiometric amount of water, based on the hydrolyzable groups present.

20. The process of claim 1 , wherein prior to mixing with the proppant the consolidating agent is present in particle-free form.

21. The process of claim 1 , wherein the proppant comprises pellets and/or particles of one or more of sand, ceramic, walnut shell, aluminum, or nylon.