Optimization of the Biocide(s) Selection and Application for Water Treatment in Oil Field

Abstract Biocides have become critical components in hydraulic fracturing fluids to inhibit or kill bacteria encountered in unconventional shale gas and oil production. Due to the unique downhole environment of each oilfield, the bacteria community varies. This often requires the further optimization of a biocide package to deliver the best performance. To address this need, we have developed a systematic biocide optimization method which comprises of DNA mapping technology, internal MBC (Minimal Biocidal Concentration) database and cATP (cellular Adenosine TriPhosphate) validation. Anaerobic sulfate/thiosulfate reducing (SRB/TRB) and acid-producing (APB) bacteria are isolated and identified as common oil field bacteria in produced water from DNA mapping. Internal MBC database of key biocides is then developed against 4 representative oil field bacteria, from which glutaraldehyde (Glut) and quaternary ammonium compounds (Quat) are selected for biocide formulation due to their complementary efficacies against SRB and TRB bacteria. The ratio between Glut and Quat is further adjusted for optimal performance efficacy and good thermal stability under oil well temperature. The new Glut/Quat biocide is then compared to Quat and oxidizing biocides, which demonstrates its faster killing rate and higher efficacy in oil field produced water, especially after repeated inoculation. The study results provide a guideline for biocide product selection for various water treatment in O&G application conditions.