Comparative Assessment of the Protective Efficiency of Co2 Corrosion Inhibitors for Gas-Field Equipment Based on Laboratory and Field Trial Results

The purpose of the article is a comparative assessment of the protective efficiency of CO2 corrosion inhibitors for gas-field equipment used to protect downhole equipment of gas-condensate wells, based on jointly interpreted field trial and laboratory results. The results of the industrial application of the corrosion inhibitors "Unicor-3", "INCO-S" and "Pachem C101G" in eight wells of two gas-condensate fields are analysed through the dynamics of total iron content (Fe2+ + Fe3+) in produced water. It is shown that the use of inhibitors reduced the iron ion content from 110–313 to 13–71 mg/dm3 in most of the studied wells, although a positive effect was not achieved in some cases. The laboratory evaluation of protective capacity was performed by gravimetric and electrochemical (linear polarization) methods in a NACE model medium and in an averaged model of formation water saturated with carbon dioxide at 50 °C for eight corrosion inhibitors of different chemical nature. It was established that most of the inhibitors provide a protection degree of 86–94 % at concetrations of 150–200 mg/L, whereas the inhibitor "KHOSP-10" showed insufficient efficiency (38.5–68.9 %) and is not recommended for further testing. For the first time, laboratory and field results for the same products were compared, showing that cases of failure to achieve the protective effect under field conditions correspond to inhibitors with the steepest conce-?tration dependence of the protection degree, which suggests under-dosing rather than the fundamental unsuitability of the product. The ability of inhibitors to form stable emulsions in the "gas condensate – formation water" system was investigated, and the dependence of emulsion separation time on the mineralization of the aqueous phase was established: separtion is slower in low-mineralized waters than in high-mineralized brines. The inhibitor "Dodicor V-4712" was found to form stable emulsions in low-mineralized wells despite its high protective efficiency, which substantiates the need for a two-tier selection criterion – protective efficiency and technological compatibility with condensate treatment. Recommendations on the optimal concentration, gas-rate-based dosing method and monitoring frequency of inhibitor protection efficiency for gas-field equipment were develped.