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1. (WO2017137788) DELAYED-EXPANSION CEMENT AND CEMENTING OPERATIONS
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CLAIMS

We Claim:

1. A delayed-expansion cement mixture comprising:

particles of hydraulic cement; and

a finely-divided, hydratable expanding agent having hydrophobically modified surfaces comprising a hydrophobic film.

2. The cement mixture according to claim 1 comprising an aqueous slurry comprising the cement particles and from 0.1 to 25 weight percent of the expanding agent, by total weight of the cement particles and the expanding agent.

3. The cement mixture according to claim 1 or claim 2, wherein the expanding agent

comprises a hydratable compound selected from the group consisting of alkaline earth metal oxides and alkaline earth metal salts.

4. The cement mixture according to any one of claims 1 to 3, wherein the hydraulic cement particles have hydrophilic surfaces and comprise Portland cement, calcium aluminate cement, fly ash, blast furnace slag, a lime/silica blend, magnesium oxychloride, a

geopolymer, zeolite, chemically bonded phosphate ceramic, or a combination thereof.

5. The cement mixture according to any one of claims 1 to 4, wherein the expanding agent is surface-modified with a hydrophobic film precursor compound having the structure Y-Z-(CQ2)n-W-X wherein:

Y is H, a halogen, or a hydrophobic moiety having m carbon atoms where m is from 1 to about 40;

Z is a covalent bond or an organic linking group having m' carbon atoms;

Q is H or F;

n is from 1 to about 40, provided that m+m'+n is from about 6 to about 40; W is a covalent bond or an organic linking group; and

X is a moiety having an affinity for the expanding agent.

6. The cement mixture according to claim 5, wherein Y is H, F, or a perfluoroalkyl group of the formula (CmX2m+i) where m is up to about 10.

7. The cement according to claim 5 or claim 6, wherein X is selected from the group consisting of phosphonate, phosphonic acid, halosilyl, alkoxysilyl, and combinations thereof.

The cement mixture according to any one of claims 1 to 7, wherein the expanding agent surface-modified with an organophosphonic acid compound according to the formula R- P(0)(OH)2 wherein R is alkyl having from 6 to 32 carbon atoms.

9. The cement mixture according to any one of claims 1 to 7, wherein the expanding agent is surface-modified with a perfluoroalkyl-alkylene-phosphonic acid compound according to the formula (CmF2m+1)(CH2)n-P(0)(OH)2 wherein m is from 1 to 10, and m+n is from 6 to

32.

10. The cement mixture according to any one of claims 1 to 9, wherein the expanding agent is surface-modified with an organosilane compound according to the formula R-SiX3 wherein R is alkyl having from 6 to 32 carbon atoms and X is halogen or alkoxy having up to 4 carbon atoms.

11. The cement mixture according to any one of claims 1 to 9, wherein the expanding agent is surface-modified with a perfluoroalkyl-alkenyl-silane compound according to the formula (CmF2m+i)(CH2)n-SiX3 wherein m is from 1 to 10, m+n is from 6 to 32, and X is halogen or alkoxy having up to 4 carbon atoms.

12. A method to delay expansion of hydraulic cement, comprising:

treating particles of a hydratable expanding agent with a hydrophobic film precursor

compound to form a finely-divided hydratable expanding agent having

hydrophobically modified surfaces;

combining the treated expanding agent with water and particles of hydraulic cement to form a settable cement slurry comprising the cement mixture according to any one of claims 1 to 11;

hardening the slurry to a set cement; and

expanding the set cement.

13. A method to cement a subterranean well having a borehole, comprising:

(i) mixing particles of hydraulic cement with a finely-divided hydratable expanding agent having hydrophobically modified surfaces to form the cement mixture according to any one of claims 1 to 11 ;

(ii) placing the cement mixture in a downhole region of the well;

(iii) hardening the cement mixture to form a set cement; and

(iv) hydrating the expanding agent to expand the set cement.

14. The method according according to claim 13, further comprising:

placing the cement mixture in an annular region of the well between a first tubular body and a borehole wall or a second tubular body; and

transversely compressing the set cement between the first tubular body and the borehole wall or second tubular body to maintain bonding therewith.

15. The method according according to claim 14, further comprising maintaining the bond

between the first tubular body and the set cement while measuring an acoustic impedance, an amplitude, an attenuation, or a bond index, or a combination thereof.

16. The method according to claim 14 or claim 15, further comprising maintaining the bond between the first tubular body and the set cement, after fluctuating the dimensions of the first tubular body in response to a temperature change, a pressure change, or a mechanical disturbance resulting from a well intervention, or a combination thereof.

17. The method according to any one of claims 14 to 16, further comprising maintaining the bond between the borehole wall and the set cement to isolate a zone of the formation adjacent the expanded cement.

18. The method according to any one of claims 14 to 17, further comprising maintaining the bond between the borehole wall and the set cement, after fluctuating the dimensions of the first tubular body in response to a temperature change, a pressure change, or a mechanical disturbance resulting from a well intervention, or a combination thereof.