Biocide Stability and Efficacy in Soured Oilfield Environments

摘要

One of the most problematic and costly microbial issues of the oil and gas industry is biotic reservoir souring. Reservoir souring can be minimized by proper treatment of injection water to control sulfate-reducing bacteria (SRB). However, control of this process is often lost due to unintended interaction of the biocidal active species with hydrogen sulfide resulting in the deleterious production of H_2S in production wells. This study investigates the stability and efficacy of commonly used oil and gas biocides in a soured environment to determine their suitability for use in souring remediation. Experiments were designed to measure biocide concentration as a function of time in the presence of dissolved sulfide using high performance liquid chromatography (HPLC) to determine the stability of various biocides. In these experiments, dissolved sulfide concentrations were also measured using the methylene blue assay to understand the interaction of biocide with sulfide. Furthermore, biocidal efficacy studies were performed against sulfate reducing bacteria to determine minimum cidal concentration (MCC) of each of these biocides in soured systems using 96-well plate most probable number assay. The panel of biocides showed varying stability when exposed to the soured environment. Depending on the biocide, decreases in the sulfide levels over time were also observed. Accordingly, the efficacy of various biocides against planktonic bacteria also changed with corresponding changes in MCC. These results offer guidance for selection of biocides that will remain stable and efficacious in soured systems.