Traditional biocide treatment for control of sulfate reducing prokaryotes (SRPs) and acid producing bacteria (APB) in oil and gas operations typically targets topside operations and often neglects the reservoir. Often, the efficacy of these biocide program is limited and do not extend for longer periods into the reservoir. This study evaluates the performance of glutaraldehyde, the most widely used effective biocide, for reservoir protection along with a synergistic combination of oxazolidine biocides. This combination provides medium to long term protection of the system and thereby controls both mesophilic and thermophilic bacteria in the reservoir.

Produced water samples from a conventional reservoir from the Middle East and Africa and unconventional reservoir from the United States were collected and a novel microbial control program was tested under heat-aged conditions with a combination of glutaraldehyde and oxazolidine type biocides. This combination provided protection (3 log10 reduction of viable counts) against repeated APB/SRP inoculation over a 30 to 64 days’ time frame at varied biocide concentrations. Th results from the heat-aging of the produced water and biocide at 75°C showed that the effectiveness of this combination can be successfully applied to achieve long term protection against biological souring in the reservoir.