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Method and composition for sealing a borehole. A chemically bonded phosphate ceramic sealant for sealing, stabilizing, or plugging boreholes is prepared by combining an oxide or hydroxide and a phosphate with water to form slurry. The slurry is introduced into the borehole where the seal, stabilizat

Method and composition for sealing a borehole. A chemically bonded phosphate ceramic sealant for sealing, stabilizing, or plugging boreholes is prepared by combining an oxide or hydroxide and a phosphate with water to form slurry. The slurry is introduced into the borehole where the seal, stabilization or plug is desired, and then allowed to set up to form the high strength, minimally porous sealant, which binds strongly to itself and to underground formations, steel and ceramics.

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1. A method of treating a borehole, comprising the steps of:(a) preparing slurry comprising oxide or hydroxide, phosphate, water, and an additive; (b) applying the slurry at a selected depth in a borehole; and (c) allowing the slurry to set up to form a sealant, wherein the additive decreases the po

1. A method of treating a borehole, comprising the steps of:(a) preparing slurry comprising oxide or hydroxide, phosphate, water, and an additive; (b) applying the slurry at a selected depth in a borehole; and (c) allowing the slurry to set up to form a sealant, wherein the additive decreases the porosity of the sealant. 2. The method of claim 1, wherein the oxide or hydroxide is selected from the group consisting of MgO, MnO, Al(OH)3, Al2O3, FeO, Fe2O3, Fe3O4, ZnO, Zr(OH)4, ZrO2, Y2O3, La2O3, VO3, CrO, CoO, PbO, Nd2O3, TiO2, CaSiO3, and mixtures thereof.3. The method of claim 1, wherein the oxide comprises magnesium oxide.4. The method of claim 1, wherein the oxide comprises zinc oxide.5. The method of claim 5, wherein the phosphate comprises theformula A(H2PO4)n wherein A=hydrogen, alkali metal, calcium, aluminum or ammonium;wherein n is a number from 1 to 3.6. The method of claim 1, wherein the phosphate is selected from the group consisting of phosphoric acid, NaH2PO4, KH2PO4, (NH4)H2PO4, AlH3(PO4)2, and mixtures thereof.7. The method of claim 1, wherein the phosphate comprises KH2PO4.8. The method of claim 1, wherein the phosphate comprises NaH2PO4.9. The method of claim 1, wherein the oxide comprises calcium oxide and the phosphate comprises Ca(H2PO4)2.10. The method of claim 1, wherein the oxide or hydroxide is present in a stoichiometric amount relative to the phosphate.11. The method of claim 1, wherein the oxide or hydroxide is present in an amount in the range from about 18 to about 60 weight percent and the phosphate is present in an amount in the range from about 40 to about 82 weight percent based upon total weight of the oxide or hydroxide and the phosphate.12. The method of claim 1, wherein the oxide or hydroxide is present in an amount in the range from about 20 to about 50 weight percent and the phosphate is present in an amount in the range from about 50 to about 80 weight percent based upon total weight of the oxide or hydroxide and the phosphate.13. The method of claim 1, wherein the oxide or hydroxide is present in an amount in the range from about 22 to about 34 weight percent and the phosphate is present in an amount in the range from about 66 to about 78 weight percent based upon total weight of the oxide or hydroxide and the phosphate.14. The method of claim 1, wherein the water is present in an amount in the range from about 25 to about 60 weight percent based upon total weight of the slurry.15. The method of claim 1, wherein the water is present in an amount in the range from about 30 to about 50 weight percent based upon total weight of the slurry.16. The method of claim 1, wherein the water is present in an amount in the range from about 30 to about 35 weight percent based upon total weight of the slurry.17. The method of claim 1, wherein the slurry further comprises a retardant that retards the set up of the slurry.18. The method of claim 17, wherein the retardant is selected from the group consisting of boric acid, citric acid, oleic acid, and organic retardants containing at least one inorganic component.19. The method of claim 1, wherein the slurry further comprises reinforcing material.20. The method of claim 19, wherein the reinforcing material is selected from the group consisting of glass fibers, chopped glass strands, mica, silica, aramids, carbon fibers, alumina, hollow glass spheres, hollow silica spheres, perlite, vermiculite, metal fibers, polymer fibers, copolymer fibers, silicate containing materials, and mixtures thereof.21. The method of claim 20, wherein the reinforcing material is present in an amount in the range from about greater than 0 to about 15 weight percent, based upon total weight of the slurry.22. The method of claim 1, wherein the additive is selected from the group consisting of glass-forming silicates, sodium compounds, fly ash, polymers and mixtures thereof.23. The method of claim 22, wherein the additive comprises calcium silicate.24. The method of claim 22, wherein the additive comprises fly ash.25. The method of claim 1, wherein the additive to decrease porosity is present in an amount in the range from greater than 0 to about 80 weight percent based upon total weight of the non-aqueous slurry components.26. The method of claim 1, wherein the additive to decrease porosity is present in an amount in the range from about 10 to about 70 weight percent based upon total weight of the non-aqueous slurry components.27. The method of claim 1, wherein the additive to decrease porosity is present in an amount in the range from about 2 to about 20 weight percent based upon total weight of the non-aqueous slurry components.28. The method of claim 1, wherein the slurry further comprises a surfactant.29. The method of claim 28, wherein the surfactant is selected from the group consisting of gas generating agents, metal oxide expanding agents, calcium sulfate hemihydrates and mixtures thereof.30. The method of claim 29, wherein said surfactant is present in an amount in the range from greater than 0 to about 10 weight percent based upon total weight of said slurry.31. The method of claim 1, wherein the water comprises salt water.32. The method of claim 1, wherein the water comprises seawater.33. The method of claim 1, wherein the water comprises brine.34. The method of claim 1, further comprising the step of:(d) drilling through the sealant. 35. The method of claim 1, wherein the slurry is applied by lowering a canister containing the slurry down the borehole and then extruding the slurry from the canister into the borehole.36. The method of claim 35, wherein the canister is lowered into the borehole on an electric wire line.37. The method of claim 35, wherein the canister is lowered into the borehole on coiled tubing.38. The method of claim 37, wherein the coiled tubing is in fluid communication with the canister.39. The method of claim 35, wherein the canister is lowered into the borehole through drill pipe.40. The method of claim 35, further comprising withdrawing the canister from the borehole.41. The method of claim 35, further comprising drilling through the canister after forming the sealant.42. The method of claim 1, wherein the slurry is applied by pumping it down the borehole through coiled tubing.43. The method of claim 1, wherein the slurry is pumped down the borehole through drill pipe.44. The method of claim 1, wherein the slurry is pumped directly down the borehole.45. The method of claim 1, further comprising repeating steps (a) and (b).