Bacteria Control in Unconventional High Temperature Dopwnhole Conditions During Completions

Abstract

Comparative biocidal efficacy studies were conducted using field water samples. Biocide stock solutions were made up in field waters and tested before and after thermal aging to simulate downhole thermal conditions. Biocidal efficacy was measured by serial dilution vials and ATP. Tributyl tetradecyl phosphonium chloride (TTPC) provided rapid biocidal activity against sulfate-reducing and acid-producing bacteria in multiple field water samples. It was also thermally stable and retained all of its biocidal activity through 7 days of heat aging at downhole temperatures of 85-90°C. In contrast, non-oxidizing biocides based on 2-bromo-2-nitropropane-1,3-diol, 2,2-dibromo-3-nitrilopropionamide, and glutaraldehyde/quaternary ammonium chloride lost significant biocidal activity after exposure to these same downhole temperatures. TTPC also showed excellent compatibility with anionic friction reducers. Once the efficacy and compatibility of TTPC was confirmed in lab tests, it was used on several multi-well fracs. Results of the flowback testing gave zero viable sulfate-reducing and acid-producing bacteria and ATP values of <100 pg/ml in several wells, indicating that TTPC was highly effective at controlling microbial contamination in the harsh field environment.