Method of removing calcareous or siliceous deposits or scales

1. A method of removing calcareous or siliceous deposits from hydrocarbon-producing wellbores and/or downhole screens while preventing and/or inhibiting the formation of inorganic fluoride scales, the method comprising:

(A) pumping into the wellbore penetrating a siliceous or calcareous 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;

(B) forming a BF 4 − complex; and

(C) removing inorganic or siliceous deposits from the hydrocarbon-producing wellbore and/or downhole screen and preventing and/or inhibiting the formation of inorganic fluoride scales

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 pH of the well treatment composition is between from about 0.5 to about 2.5.

3. The method of claim 1 , wherein the inorganic fluoride scales are selected from the group consisting of calcium fluoride, magnesium fluoride, sodium fluorosilicate, potassium fluorosilicate and fluoroaluminate.

4. The method of claim 1 , wherein the well treatment 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.

5. 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.

6. 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.

7. The method of claim 6 , 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.

8. 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.

9. The method of claim 8 , 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.

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

11. The method of claim 1 , wherein the amount of boron containing compound in the aqueous well treatment 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.

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

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

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

15. A method of removing calcareous or siliceous deposits while preventing and/or inhibiting the formation of inorganic fluoride scales from hydrocarbon-producing wellbores, well casings, downhole assembly, downhole screens, production equipment, recovery equipment, well tubular or pipelines which comprises:

(A) pumping into the wellbore, well casing, downhole assembly, downhole screen, production equipment, recovery equipment, well tubular or pipeline an aqueous 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;

(B) forming a BF 4 − complex; and

(C) removing the calcareous or siliceous deposits from the wellbore, well casing, downhole assembly, downhole screen, production equipment, recovery equipment, well tubular or pipeline and preventing and/or inhibiting the formation of inorganic fluoride scales

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.

16. 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, diethylenetriaminepenta (methylene phosphonic acid) and its hexasodium salt and diethylenediamine penta (methylene phosphonic) acid and its esters and sodium salt.

17. The method of claim 16 , 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.

18. The method of claim 17 , 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.

19. The method of claim 1 , wherein the hydrofluoric acid source provides between from about 0.25 to about 10 weight percent of HF to the well treatment composition.

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

21. The method of claim 15 , wherein the inorganic fluoride scales are selected from the group consisting of calcium fluoride, magnesium fluoride, sodium fluorosilicate, potassium fluorosilicate and fluoroaluminate.

22. The method of claim 15 , wherein the aqueous well treatment composition is introduced into the wellbore during a remedial workover operation.

23. The method of claim 15 , wherein the aqueous well treatment composition is introduced into the wellbore during a matrix acidizing operation.

24. A method of removing calcium fluoride, magnesium fluoride, sodium fluorosilicate, potassium fluorosilicate and/or fluoroaluminate scales from hydrocarbon-producing wellbores and/or downhole screens which comprises:

(A) pumping into the wellbore a well treatment composition having a pH between from about 0.5 to about 2.5 and 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;

(B) forming a BF 4 − complex; and

(C) removing the scales from the hydrocarbon-producing wellbore and/or downhole screen

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