Method for extending time of activity of chlorite-based biocides
This invention relates to the use of chlorite-based antimicrobials in a manner where the time of biocidal activity is extended for the microbial control in the water used for drilling, completion and remediation of wells. The invention involves mixing of a compatible extender in the form of sodium chlorate with sodium chlorite to form an antimicrobial formulation. This combination is used with an acid on the site to generate chlorine dioxide which is injected into the water used for hydraulic fracturing or remedial workover. The formulation is a much more effective bactericide for the subterranean oil and gas rich formations. The potency and longevity of biocidal activity is controlled by varying the ratios of chlorate and acid which provide different profiles of the antimicrobial activities.
1. A composition useful for treating water used in oil and gas operations comprising an aqueous solution of sodium chlorite and sodium chlorate in the weight ratio of from about 2:1 to about 1:1 and citric acid wherein the acid to sodium chlorite and sodium chlorate ratio is from about 1:20 to about 1:2, said composition providing chlorite activity in the water for a time period of about 4-7 days.
2. The composition of claim 1 further comprising salinity adjusting compound of from 1 to 20% by weight.
3. The composition of claim 2 further comprising a corrosion inhibitor.
4. The composition of claim 2 further comprising an ionic or non-ionic surfactant.
5. The composition of claim 2 wherein the salinity adjusting compound is sodium chloride.
6. The composition of claim 2 wherein the salinity adjusting compound is potassium chloride.
7. A method for treating water used in oil and gas operations comprising:
providing an aqueous precursor solution of sodium chlorite and sodium chlorate in the weight ratio of from about 2:1 to about 1:1;
adding citric acid to the precursor solution in a ratio of from about 1:20 to about 1:2 and allowing the solution to react for a period of time to generate chlorine dioxide; and
adding the reacted solution to the water to be treated for use in the well;
wherein the reacted solution provides chlorite activity in the water for a time period of about 4-7 days.
8. The method of claim 7 further comprising the step of adding a salinity adjusting compound selected from the group consisting of sodium chloride and potassium chloride.
9. The method of claim 8 wherein the salinity adjusting compound is added to a concentration of from about 1 to about 10% by weight.
10. The composition of claim 1 comprising 8-50% by weight citric acid.
11. The composition of claim 1 comprising only one Bronsted-Lowry acid.
12. The method of claim 7 whereby the reacted solution comprises 8-50% by weight citric acid.
13. A composition useful for treating water used in oil and gas operations comprising an aqueous mixture of sodium chlorite and sodium chlorate in the weight ratio of from about 25:1 to about 1:5 and citric acid wherein the acid to sodium chlorite and sodium chlorate ratio is from about 1:20 to about 1:2, wherein the composition comprises from 8-50% by weight citric acid, said composition providing chlorite activity in the water for a time period of about 4-7 days.
14. The composition of claim 1 , wherein said composition provides chlorate activity in water for a time period of at least 22 days.
15. The composition of claim 1 , wherein said composition provides chlorate activity in water for a time period of about 22 to 40 days.
16. The method of claim 7 , wherein said composition provides chlorate activity in water for a time period of at least 22 days.
17. The method of claim 7 , wherein said composition provides chlorate activity in water for a time period of about 22 to 40 days.
18. The method of claim 13 , wherein said composition provides chlorate activity in water for a time period of at least 22 days.
19. The method of claim 13 , wherein said composition provides chlorate activity in water for a time period of about 22 to 40 days.