Résumé : Microbiologically influenced corrosion (MIC) and CO2 corrosion are the common types of corrosion in shale gas fields. In this study, the effect of quaternized polyacrylamide inhibitor on MIC was studied in the produced water from a shale gas field using a circulating loop system with CO2. The result shows that polyacrylamide can inhibit CO2 corrosion. However, in the presence of microorganisms, polyacrylamide failed to inhibit MIC. Microorganisms formed biofilm on the coupon surface. Pitting nucleated underneath the biofilm and developed into cavity-type due to the local acidification. According to crystal structure and chemical composition of matters in the biofilm, the mechanism of microbial acidification leading to pitting corrosion was proposed. The prevention and control strategy for MIC in CO2 environment was discussed.