Measurement of scale inhibitor in water systems

1. A method for determining a concentration of a scale inhibitor in a water system, the method comprising:

contacting a sample of water containing scale inhibitor with a dye in a capillary channel to form a complex effective to generate fluorescence;

measuring a fluorescence signal generated by the complex; and

determining a concentration of the scale inhibitor based on the fluorescence signal.

2. The method of claim 1 , further comprising separating the scale inhibitor from an inorganic salt contained in said sample of water in the capillary channel before forming the complex.

3. The method of claim 1 , wherein the scale inhibitor comprises an anionic scale inhibitor.

4. The method of claim 1 , wherein the scale inhibitor comprises a phosphate ester; a phosphonate; a polycarboxylate; a phosphine polymer; a sulfonate; polyvinyl sulfate; or a combination comprising at least one of the foregoing.

5. The method of claim 1 , wherein said sample of water comprises less than about 15 weight percent (wt %) of sodium chloride, sodium acetate, and sodium sulfate, or a combination thereof, wherein said wt % is based on a total weight of said sample of water.

6. The method of claim 1 , further comprising the step of diluting said sample of water so that the concentration of sodium chloride, sodium acetate, and sodium sulfate, or a combination thereof is less than 15 weight percent (wt %) before said measuring step, wherein said wt % is based on a total weight of said sample of water.

7. The method of claim 1 , wherein said water sample is from a water system that is an oilfield fluid comprising seawater, formation water, produced water, a drilling fluid, a completion fluid, a stimulating fluid, a squeezing fluid, or a combination comprising at least one of the foregoing.

8. The method of claim 1 , further comprising filling the capillary channel with an electrolyte, and introducing said water sample comprising the scale inhibitor to the capillary channel filled with the electrolyte.

9. The method of claim 8 , wherein the electrolyte comprises a buffer salt and a polymer.

10. The method of claim 8 , wherein the electrolyte has a pH of about 7 to about 10.

11. The method of claim 8 , wherein the electrolyte further comprises an amino acid.

12. A method for determining a concentration of a scale inhibitor in a water system, the method comprising:

providing a capillary channel having an inlet end and an outlet end, wherein the capillary channel is filled with an electrolyte comprising a buffer salt, a polymer, and a dye;

loading a sample containing a scale inhibitor into the capillary channel from the inlet end;

forming a fluorescent complex of the scale inhibitor and the dye;

measuring a fluorescence signal generated by the complex; and

determining the concentration of the scale inhibitor based on the fluorescence signal.

13. The method of claim 12 , further comprising separating the scale inhibitor from a salt in the sample before forming the complex.

14. A method of treating a water system, the method comprising:

introducing an effective amount of a scale inhibitor to a water system;

obtaining a sample of the water system containing the scale inhibitor;

contacting the scale inhibitor in the sample with a dye in a capillary channel to produce a complex effective to generate fluorescence;

measuring a fluorescence signal generated by the complex;

determining a concentration of the scale inhibitor based on the fluorescence signal; and

adding an additional quantity of a scale inhibitor to the water system if the measured concentration is below a given value.

15. The method of claim 14 , further comprising separating the scale inhibitor from a salt in the sample before forming the complex.

16. The method of claim 14 , wherein the scale inhibitor comprises an anionic scale inhibitor.