Claims
- 1. A method for removing alkaline earth sulfate scale comprising contacting the scale with an aqueous solution having a pH of about 8 to about 14 and comprising a chelating agent comprising a polyaminopolycarboxylic acid present in a concentration of from 0.1 M to 1.0 M or salt of such an acid, and a synergist which comprises oxalate anions present in a concentration of from 0.1 M to 1.0 M to dissolve the scale.
- 2. The method as recited in claim 1 where the chelating agent comprises DTPA.
- 3. The method as recited in claim 1 where the pH of the solution is from 11 to 13.
- 4. The method as recited in claim 1 where the pH of the solution is about 12.
- 5. The method as recited in claim 1 where the scale is contacted with the solution at a temperature from 25.degree. C. to 100.degree. C.
- 6. The method as recited in claim 1 where the scale comprises barium sulfate scale.
- 7. The method as recited in claim 1 where the scale is contacted with the solution for a time of up to 4 hours.
- 8. The method as recited in claim 1 where the pH of the solution is provided by the use of a potassium base.
- 9. The method as recited in claim 8 where the potassium base is potassium hydroxide.
- 10. The method as recited in claim 1 where the scale comprises barium, strontium, or calcium sulfate and mixtures thereof.
- 11. The method as recited in claim 1 where about 80% to about 90% of a saturation level of barium, strontium or calcium sulfate is dissolved from the scale in about 10 minutes at a temperature of about 100.degree. C.
- 12. The method as recited in claim 1 where the solution is directed down a cased wellbore, from which the scale is dissolved and subsequently dissolved scale is removed from the wellbore.
- 13. The method as recited in claim 1 where the solution is contacted with a subsurface formation to remove scale from the formation.
- 14. The method as recited in claim 1 where the sulfate scale contains radium.
CROSS-REFERENCE TO RELATED APPLICATIONS
This application is a continuation part of prior co-pending application Ser. No.07/332,147, filed Apr. 3, 1989, of J. M. Paul and R. L. Morris.
US Referenced Citations (6)
Foreign Referenced Citations (2)
Number |
Date |
Country |
61-174990 |
Jan 1985 |
JPX |
63-178199 |
Jan 1987 |
JPX |