Chemically bonded phosphate ceramic sealant formulations for oil field applications

1. A sealant for an oil or geothermal well capable of setting within about 3 to about 6 hours at temperatures less than about 250° F. for shallow wells less than about 10,000 feet and deep wells greater than about 10,000 feet, said sealant being comprised of:

a) MgO present in the range of from about 9.9 to about 14.5% by weight of said sealant,

b) KH 2 PO 4 present in the range of from about 29.7 to about 27.2% by weight of said sealant,

c) class C fly ash present in the range of from about 19.8 to about 36.3% by weight of said sealant,

d) class F fly ash present in the range of from about 19.8 to about 0% by weight of said sealant,

e) boric acid or borax present in the range of from about 0.39 to about 1.45% by weight of said sealant, and

f) water present in the range of from about 20.3 to about 21.86% by weight of said sealant.

2. The sealant of claim 1 , wherein said MgO is present at about 10% and said KH 2 PO 4 is present at about 30% and said class C fly ash is present at about 20% and said class F fly ash is present at about 20% and said boric acid or borax is present at about 0.4% and fresh water if present is at about 20% and salt water if present is at about 22% of said sealant, said sealant being adapted for shallow wells less than about 10,000 feet and at temperatures of less than about 150° F.

3. The sealant of claim 1 , wherein said MgO is present at about 10% and said KH 2 PO 4 is present at about 30% and said class C fly ash is present at about 40% and said class F fly ash is substantially absent and said boric acid or borax is present at about 0.4% and fresh water if present is at about 20% and salt water if present is at about 22% of said sealant, said sealant being adapted for deep wells greater than about 10,000 feet.

4. The sealant of claim 3 , wherein at least some wollastonite is substituted for class C fly ash.

5. The sealant of claim 1 , wherein at least some sand is substituted for class C fly ash to adjust setting times.

6. The sealant of claim 1 and further comprising lightweight or heavyweight material added to said slurry to vary the density of said slurry from about 0.5 g/cm 3 to about 1.8 g/cm 3 .

7. The sealant of claim 6 , wherein said lightweight material is a plurality of hollow silica spheres.

8. The sealant of claim 6 , wherein said heavyweight material is a mineral such as haematite or magnetite or an equivalent thereof.

9. The sealant of claim 1 , wherein said MgO is calcined at a temperature not less than about 1300° C. for not less than about 3 hours.

10. The sealant of claim 1 , wherein class F fly ash is substantially free of excess calcium.

11. The sealant of claim 1 , wherein the sealant constituents other than water are powders having average sizes of about 10 microns.

12. A premixed powder for aqueous slurry of a sealant for an oil or gas well, said premixed powder comprising

a) MgO present in the range of from about 12.3% to about 18% by weight of said premixed powder,

b) KH 2 PO 4 present in the range of from about 37% to about 34% by weight of said premixed powder,

c) class C fly ash present in the range of from about 24.75% to about 45.3% of said premixed powder,

d) class F fly ash present in the range of from about 24.75% to about 0% by weight of said premixed powder, and

e) boric acid or borax present in the range of from 0.48 to about 1.81% by weight of said premixed powder.

13. The premixed powder of claim 12 , wherein at least some wollastonite is substituted for class C fly ash.

14. The sealant of claim 12 , wherein at least some sand is substituted for class C fly ash to adjust setting times.

15. The sealant of claim 12 and further comprising lightweight or heavyweight material added to said slurry to vary the density of said slurry from about 0.5 g/cm 3 to about 1.8 g/cm 3 .

16. The premixed powder of claim 12 , wherein the sealant constituents other than water are powders having average sizes of about 10 microns.