Determination of Field Chemicals: Corrosion Inhibitor (CI) and Kinetic Hydrate Inhibitor (KHI) in Produced Water

摘要

Corrosion inhibitors (CI) and hydrate inhibitors are among the few but essential field chemicals added in oil and gas production operations as a part of fluid flow assurance. While CI is added regularly to prevent corrosion, hydrate inhibitors are used only during cold season in order to prevent the formation of gas hydrates. A new generation of hydrate inhibitors, namely kinetic hydrate inhibitors (KHI), is becoming more attractive than thermodynamic inhibitors, since lower dosage of KHI is typically needed. Monitoring of residual field chemicals in produced water is essential for flow assurance issues; and is also of particular concern to better understand the needs for water treatment options, and to evaluate their environmental impacts. The corrosion and hydrate inhibitors bring several challenges associated with their determination and characterization in produced water. The challenges include identification of the interferences and enhancing the selectivity and sensitivity for these chemicals. This paper evaluates selective analytical methodologies for the analyses of CI and KHI in produced water. The paper also addresses improvements in enhanced detection and accuracy of these field chemicals. The CI is analyzed by high performance liquid chromatography (HPLC) with UV detection. The brine composition and pH of the eluting solutions have to be adjusted to minimize the associated matrix effects. Besides, CI analyses suffer from low UV-absorption of key components, which limits their quantitation. The use of a Corona detector in conjunction with HPLC to achieve desired sensitivity is evaluated, with emphasis on peak separation of key CI components. The methods evaluated for KHI analyses are colorimetric, iodine complexation, and size exclusion chromatography (SEC). The colorimetric method is subject to intense interference by CI, limiting its application for KHI determination in the presence of CI blends. The iodine complexation method is chosen as a practical wet chemical method for KHI analysis.lt is modified to minimize the interferences due to brine concentration, corrosion inhibitor, condensate, and sulfide. However, the selectivity of the iodine complexation method is still not at the desired level. As an improvement to selectivity and accuracy, the SEC method is evaluated. The SEC method offers better selectivity and characterization of KHI. The characterization of molecular weight distribution is critical in the evaluation of treatment and removal efficiency of KHI in produced water streams.