BACKGROUND Microbial corrosion is a serious challenge for the oil and gas industry worldwide, leading to huge economic losses and production issues. Successful mitigation of microbial corrosion requires a complete characterization of the microbial community present in the system. This paper deals with the extensive microbial analysis and study of performance of biocide formulations for different water types in an oilfield. RESULTS Water, solid and coupon samples were collected at various points in the production system and analyzed for total microbial numbers by quantitative polymerase chain reaction (qPCR) and microbial diversity using next-generation sequencing (NGS). A high-throughput multi-well system was used to screen eight different biocide formulations at various dosage levels. A pipeline simulator reactor was developed and used to represent field conditions such as temperature, flow and shear rates. The tests showed that the dominant microbial species causing corrosion were sulfate-reducing Desulfovibrio spp. in seawater and brackish water systems and acid-producing fermentative Halanaerobium spp. in effluent water. The results showed that different biocide treatment strategies have to be adopted for treating different water types. Biocide formulations containing ADBAC and THPS + surfactant showed the most promising results for seawater, whereas biocide formulations of ADBAC and THPS + glutaraldehyde performed better for brackish and effluent waters. CONCLUSION The study has shown that molecular methods such as qPCR and NGS provide better and accurate evaluation of the microbial community in the field compared with conventional growth-based methods, leading to optimized mitigation strategies. (c) 2019 Society of Chemical Industry