Long-standing techniques for alkalinity determination in oilfield brines were derived from analysis of potable water as given in standard methods guidebooks (APHA, 1985). Such traditional potable water methods are unable discriminate the contribution from the naturally occurring organic anions. This lack of sensitivity has led to higher scale-inhibitor costs than would be indicated using the technique presented here. Other industry-accepted methods have demonstrated the ability to parse the organic and inorganic alkalinity components but are time consuming and unsuited for the brisk pace of a production lab environment.

A rapid and robust method employing classical acid-base titration techniques has been developed to meet the requirements of advanced scale-prediction models. This method involves two separate titrations; one using 0.10 N hydrochloric acid followed by a back-titration using 0.10 N sodium hydroxide.

Standard solutions of bicarbonate and acetate blended at set proportions were employed to determine total alkalinity and organic acid content using this manual technique. The bicarbonate ion is estimated by subtracting organic acids from titrated total alkalinity.

The validation of the automated implementation of this method shows strong reproducibility and accuracy that is achieved in less than fifteen minutes. The new alkalinity method provides quality data for scale modeling.

More than one hundred runs of the newly developed method have shown excellent reproducibility from field locations in Texas, Louisiana, Utah, Colorado and Oklahoma. The laboratory adaptation using an auto-titrator has shown good correlation with the manual field method, and it can be automated for a high-throughput commercial laboratory. Concentrations of iron above 30 mg/l can interfere with the method if oxidation is allowed.

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