Methods and systems for removing geothermal scale

1. A method comprising:

introducing a descaling agent comprising an N-(phosphonoalkyl)iminodiacetic acid or any salt thereof into a wellbore of a geothermal well, the geothermal well having a bottom-hole temperature of about 300° F. or greater and having geothermal scale present therein;

contacting the geothermal scale with the descaling agent; and

removing at least a portion of the geothermal scale from the geothermal well using the descaling agent,

wherein removing at least a portion of the geothermal scale comprises dissolving at least a portion of the geothermal scale with the descaling agent to produce a metal ion, and complexing the metal ion with the N-(phosphonoalkyl)iminodiacetic acid or any salt thereof, and wherein the geothermal scale comprises a siliceous material and a metal-containing compound.

2. The method of claim 1 , wherein the metal ion comprises at least one metal ion selected from the group consisting of an iron ion, a copper ion, a silver ion, a magnesium ion, a calcium ion, an aluminum ion, a manganese ion, a nickel ion, a barium ion, a strontium ion, a zirconium ion, a zinc ion, a titanium ion, a tin ion, a beryllium ion, an antimony ion, an arsenic ion, and any combination thereof.

3. The method of claim 1 , wherein the descaling agent further comprises hydrofluoric acid or a hydrofluoric acid-generating compound.

4. The method of claim 3 , wherein the descaling agent is introduced into the wellbore in a treatment fluid that contains about 1 wt. % or less alkali metal ions.

5. The method of claim 1 , wherein the geothermal scale comprises up to about 50 wt. % of the siliceous material.

6. The method of claim 1 , wherein the siliceous material comprises silica, a silicate, an aluminosilicate, or any combination thereof.

7. The method of claim 1 , wherein the geothermal scale is present in the wellbore, in a fracture of a subterranean formation penetrated by the wellbore, on a tool present in the wellbore, or any combination thereof.

8. The method of claim 1 , wherein the descaling agent further comprises hydrofluoric acid or a hydrofluoric acid-generating compound.

9. The method of claim 1 , wherein the N-(phosphonoalkyl)iminodiacetic acid has a structure of

wherein n is an integer ranging between 1 and about 5.

10. The method of claim 9 , wherein the N-(phosphonoalkyl)iminodiacetic acid comprises N-(phosphonomethyl)iminodiacetic acid or any salt thereof.

11. A method comprising:

introducing a treatment fluid comprising a descaling agent into a wellbore of a geothermal well, the geothermal well having a bottom-hole temperature of about 300° F. or greater and having geothermal scale comprising a metal-containing compound present therein, the descaling agent comprising an N-(phosphonoalkyl)iminodiacetic acid or any salt thereof;

dissolving at least a portion of the geothermal scale with the descaling agent to produce a metal ion; and

complexing the metal ion with the N-(phosphonoalkyl)iminodiacetic acid.

12. The method of claim 11 , wherein the treatment fluid contains about 1 wt. % or less alkali metal ions.

13. The method of claim 11 , wherein the metal ion comprises at least one metal ion selected from the group consisting of an iron ion, a copper ion, a silver ion, a magnesium ion, a calcium ion, an aluminum ion, a manganese ion, a nickel ion, a barium ion, a strontium ion, a zirconium ion, a zinc ion, a titanium ion, a tin ion, a beryllium ion, an antimony ion, an arsenic ion, and any combination thereof.

14. The method of claim 11 , wherein the geothermal scale further comprises a siliceous material.

15. The method of claim 14 , wherein the descaling agent further comprises hydrofluoric acid or a hydrofluoric acid-generating compound.

16. The method of claim 14 , wherein the geothermal scale comprises up to about 50 wt. % of the siliceous material.

17. The method of claim 11 , wherein the descaling agent further comprises hydrofluoric acid or a hydrofluoric acid-generating compound.

18. The method of claim 11 , wherein the N-(phosphonoalkyl)iminodiacetic acid has a structure of

wherein n is an integer ranging between 1 and about 5.

19. The method of claim 18 , wherein the N-(phosphonoalkyl)iminodiacetic acid comprises N-(phosphonomethyl)iminodiacetic acid or any salt thereof.

20. The method of claim 11 , wherein the N-(phosphonoalkyl)iminodiacetic acid or any salt thereof is present as a solid in the treatment fluid and is introduced to the geothermal well in a slurry form.

21. A method comprising:

contacting geothermal scale with a descaling agent comprising an N-(phosphonoalkyl)iminodiacetic acid or any salt thereof;

dissolving at least a portion of the geothermal scale with the descaling agent to produce a metal ion; and

complexing the metal ion with the N-(phosphonoalkyl)iminodiacetic acid or any salt.

22. The method of claim 21 , wherein the descaling agent further comprises hydrofluoric acid or a hydrofluoric acid-generating compound.

23. The method of claim 21 , wherein the geothermal scale is present in a wellbore, in a fracture of a subterranean formation penetrated by the wellbore, on a tool present in the wellbore, on a surface structure in fluid communication with the wellbore, or any combination thereof.

24. A system comprising:

a pump fluidly coupled to a tubular, the tubular containing a treatment fluid comprising a descaling agent comprising an N-(phosphonoalkyl)iminodiacetic acid or any salt thereof,

wherein the tubular extends into a wellbore of a geothermal well, the geothermal well having a bottom-hole temperature of about 300° F. or greater and having geothermal scale present therein, wherein removing at least a portion of the geothermal scale comprises dissolving at least a portion of the geothermal scale with the descaling agent to produce a metal ion, and complexing the metal ion with the N-(phosphonoalkyl)iminodiacetic acid or any salt thereof, and wherein the geothermal scale comprises a siliceous material and a metal-containing compound.