Method for controlling inorganic fluoride scales

1. A method for enhancing the productivity of a hydrocarbon-bearing calcareous or siliceous formation which comprises:

(A) introducing into a wellbore penetrating the formation an aqueous well treating composition comprising:

(a) a boron containing compound selected from the group consisting of (i.) fluoroboric acid and (ii.) boron compounds capable of forming a BF 4 − complex when exposed to F 4 − or a hydrofluoric acid source;

(b) a phosphonate acid, ester or salt thereof, wherein the phosphonate is of the formula:

wherein R1, R2 and R3 are independently selected from hydrogen, alkyl, aryl, phosphonic, phosphonate, phosphate, aminophosphonic acid, aminophosphonate, acyl, amine, hydroxy and carboxyl groups and R4 and R5 are independently selected from hydrogen, sodium, potassium, ammonium or an organic radical; and

(c) a hydrofluoric acid source; and

(B) preventing and/or inhibiting the formation of inorganic fluoride scales in the wellbore and/or formation by forming a BF 4 − complex and thereby enhancing the productivity of the formation

wherein the combination of boron containing compound and the phosphonate acid, ester or salt creates a synergistic effect such that the amount of inorganic fluoride scales precipitated in the presence of the combination is less than the amount of inorganic fluoride scales precipitated when either the boron containing compound or phosphonate acid, ester or salt is used alone.

2. The method of claim 1 , wherein the aqueous well treating composition prevents and/or inhibits the formation of scales of at least one inorganic fluoride selected from the group consisting of calcium fluoride, magnesium fluoride, sodium fluorosilicate, potassium fluorosilicate and fluoroaluminate.

3. The method of claim 1 , wherein the phosphonate acid, ester or salt thereof is selected from the group consisting of aminotri (methylene phosphonic acid) and its esters and pentasodium salt, 1-hydroxyethylidene-1,1-diphosphonic acid and its esters and tetrasodium salt, hexamethylenediaminetetra (methylene phosphonic acid) and its esters and hexapotassium salt, and diethylenetriaminepenta (methylene phosphonic acid) and its esters and sodium salt.

4. The method of claim 3 , wherein the phosphonate acid, ester or salt thereof is selected from the group consisting of aminotri (methylene phosphonic acid), 1-hydroxyethylidene-1,1-diphosphonic acid, hexamethylenediaminetetra (methylene phosphonic acid), diethylenetriaminepenta (methylene phosphonic acid) and diethylenediamine penta (methylene phosphonic) acid.

5. The method of claim 3 , wherein the phosphonate acid, acid, ester or salt thereof is selected from the group consisting of 1-hydroxyethylidene-1,1-diphosphonic acid and diethylenediamine penta (methylene phosphonic) acid.

6. The method of claim 1 , wherein the boron containing compound is a boron compound capable of forming a BF 4 − complex when exposed to a hydrofluoric acid source.

7. The method of claim 6 , wherein the hydrofluoric acid source provides between from about 0.25 to about 10 weight percent of HF to the aqueous well treatment composition.

8. The method of claim 1 , wherein the pH of the aqueous well treating composition is between from about 0.5 to about 2.5.

9. The method of claim 1 , wherein the formation contains dolomite.

10. A method of increasing the permeability of a hydrocarbon-bearing calcareous or siliceous formation which comprises

(A) introducing into a wellbore penetrating the calcareous or siliceous formation an aqueous well treating composition comprising:

(a) a boron containing compound selected from the group consisting of (i.) fluoroboric acid and/or (ii.) boron compounds capable of forming a BF 4 − complex when exposed to F 4 − or a hydrofluoric acid source;

(b) a phosphonate acid, ester or salt thereof, wherein the phosphonate is of the formula:

wherein R1, R2 and R3 are independently selected from hydrogen, alkyl, aryl, phosphonic, phosphonate, phosphate, aminophosphonic acid, aminophosphonate, acyl, amine, hydroxy and carboxyl groups and R4 and R5 are independently selected from hydrogen, sodium, potassium, ammonium or an organic radical; and

(c) a hydrofluoric acid source; and

(B) preventing and/or inhibiting the formation of inorganic fluoride scales upon formation of BF 4 − in the calcareous or siliceous formation and/or wellbore and thereby increasing the permeability of the calcareous or siliceous formation

wherein the combination of boron containing compound and the phosphonate acid, ester or salt thereof creates a synergistic effect such that the amount of inorganic fluoride scales precipitated in the presence of the combination is less than the amount of inorganic fluoride scales precipitated when either the boron containing compound or phosphonate acid, ester or salt is used alone.

11. The method of claim 10 , wherein the aqueous well treating composition prevents and/or inhibits the formation of scales of at least one inorganic fluoride selected from the group consisting of calcium fluoride, magnesium fluoride, sodium fluorosilicate, potassium fluorosilicate and fluoroaluminate.

12. The method of claim 10 , wherein the phosphonate acid, ester or salt thereof is selected from the group consisting of aminotri (methylene phosphonic acid) and its pentasodium salt, 1-hydroxyethylidene-1,1-diphosphonic acid and its tetrasodium salt, hexamethylenediaminetetra (methylene phosphonic acid) and its hexapotassium salt, and diethylenetriaminepenta (methylene phosphonic acid) and its hexasodium salt.

13. The method of claim 10 , wherein the boron containing compound is a boron compound capable of forming a BF 4 − complex when exposed to a hydrofluoric acid source.

14. The method of claim 13 , wherein the hydrofluoric acid source provides between from about 0.25 to about 10 weight percent of hydrofluoric acid to the aqueous well treating composition.

15. The method of claim 10 , wherein the pH of the aqueous well treating composition is between from about 0.5 to about 2.5.

16. A method of preventing and/or inhibiting the formation of calcium fluoride and/or magnesium fluoride scales in a hydrocarbon-bearing calcareous or siliceous formation which comprises:

(A) introducing into the formation a well treatment composition comprising:

(a) a boron containing compound selected from the group consisting of (i.) fluoroboric acid and/or (ii.) boron compounds capable of forming a BF 4 − complex when exposed to F 4 − or a hydrofluoric acid source;

(b) a phosphonate acid, ester or salt thereof, wherein the phosphonate is of the formula:

wherein R1, R2 and R3 are independently selected from hydrogen, alkyl, aryl, phosphonic, phosphonate, phosphate, aminophosphonic acid, aminophosphonate, acyl, amine, hydroxy and carboxyl groups and R4 and R5 are independently selected from hydrogen, sodium, potassium, ammonium or an organic radical; and

(c) a hydrofluoric acid source; and

(B) forming a BF 4 − complex and thereby preventing and/or inhibiting the formation of inorganic fluoride scales in the wellbore and/or formation

wherein the combination of boron containing compound and the phosphonate acid, ester or salt thereof creates a synergistic effect such that the amount of inorganic fluoride scales precipitated in the presence of the combination is less than the amount of inorganic fluoride scales precipitated when either the boron containing compound or phosphonate acid, ester or salt is used alone.

17. The method of claim 1 , wherein the amount of phosphonate acid, ester or salt thereof in the aqueous well treating composition is between from about 0.1 to about 10 percent by volume based on the total volume of (b) and (c) and water.

18. The method of claim 1 , wherein the boron containing compound is of the formula R 6 R 7 R 8 BO 3 wherein each of R 6 , R 7 and R 8 are independently hydrogen or a unsubstituted or substituted alkyl or alkylene group.

19. The method of claim 18 , wherein each of R 6 , R 7 and R 8 is independently selected from hydrogen or C 1 -C 4 alkyl group, optionally substituted with one or more —OH groups.

20. The method of claim 1 , wherein the boron containing compound is of the formula:

wherein each of R 9 , R 10 , R 11 , R 12 , R 13 , R 14 , R 15 and R 16 is independently selected from hydrogen or a substituted or unsubstituted alkyl or alkenyl group.

21. The method of claim 20 , wherein each of R 9 , R 10 , R 11 , R 12 , R 13 , R 14 , R 15 and R 16 is independently selected from hydrogen or a C 1 -C 4 alkyl group, optionally substituted with one or more —OH groups.

22. The method of claim 1 , wherein boron containing compound is boric acid or a salt thereof.

23. The method of claim 1 , wherein the amount of boron containing compound in the aqueous well treating composition is that sufficient to render between from about 0.5 to about 10 g BF 4 − complex per 100 cc of (b), (c) and water.

24. The method of claim 1 , wherein the aqueous well treating composition further comprises at least one member selected from the group consisting of corrosion inhibitors, mutual solvents, alcohols, iron control agents, non-emulsifiers, clay stabilizers and water-wetting surfactants.

25. The method of claim 1 , wherein the aqueous well treatment composition is introduced into the wellbore during a fracturing operation.

26. The method of claim 1 , wherein the aqueous well treatment composition is introduced into the wellbore during a remedial workover operation.

27. The method of claim 1 , wherein the aqueous well treatment composition is introduced into the wellbore during a matrix acidizing operation.

28. The method of claim 10 , wherein the amount of phosphonate acid, ester or salt thereof in the aqueous well treating composition is between from about 0.1 to about 10 percent by volume based on the total volume of (b) and (c) and water.

29. The method of claim 16 , wherein the well treating composition further comprises at least one member selected from the group consisting of corrosion inhibitors, mutual solvents, alcohols, iron control agents, non-emulsifiers, clay stabilizers and water-wetting surfactants.

30. The method of claim 16 , wherein the pH of the aqueous well treating composition is between from about 0.5 to about 2.5.