Well acidizing treatments are conducted to enhance rock permeability, remove or bypass formation damage. During field applications, corrosion inhibitors are extensively used, among many other additives, to protect well tubulars against acid attack. The inhibitors are complex mixtures containing: quaternary salts, acetylenic alcohols, surfactants, solvents and impurities. Therefore, several analytical techniques and instruments are needed to characterize these compounds.

Capillary electrophoresis (CE) is a rapid and reliable analytical separation technique. It has significantly improved over the last two decades to include a wide range of analytical applications, such as: food, pharmaceutical and biomedical industries. Coupling CE to universal detectors, such as Mass Spectrometry (MS) can boost the analytical ability of this instrument in qualitative and quantitative applications.

In a previous work (SPE 58801) the authors adopted a CE technique to monitor the level of key oxygenated compounds in acid additives that are also used in deep, hot and sour gas wells. In the present work, the use of capillary electrophoresis-mass spectrometry (CE-MS), chromatographic and spectrometric techniques, to identify key nitrogen compounds in acid corrosion inhibitors was investigated. The inhibitors were selected from several commercial products that are commonly used in the field.

Capillary electrophoresis was also applied for quantitative measurement of the inhibitor's level in well fluids, based on the response of its key nitrogen compounds. A linear relationship was obtained for the inhibitors of interest. The cation selected was a quinoline-based quaternary salt. This cation was detected down to inhibitor's level of 0.023 wt% with an analytical precision of less than 10%.

The CE technique was used to determine the level of the corrosion inhibitors during acid fracturing treatments of deep gas wells.

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