Long-Term Biocide Efficacy and Its Effect on a Souring Microbial Community

Area of Science:

• Microbial Ecology
• Petroleum Geochemistry
• Environmental Microbiology

Background:

• Reservoir souring, caused by sulfate-reducing microorganisms (SRM), is a persistent challenge in the oil industry, leading to infrastructure corrosion and safety risks.
• Current biocide treatments offer temporary solutions, with limited understanding of their long-term efficacy and the microbial community's response, hindering effective souring control.

Purpose of the Study:

• To investigate the long-term effectiveness of glutaraldehyde (GA) and aldehyde-releasing biocide (ARB) treatments against reservoir souring.
• To analyze the impact of biocide treatments on microbial community structure, diversity, and abundance over one year.
• To identify microbial indicators for predicting biocide treatment failure in oil reservoirs.

Main Methods:

• Application of single biocide treatments (GA and ARB) at low (100 ppm) and high (750 ppm) doses to a complex SRM community.
• One-year monitoring of chemical parameters (souring indicators) and microbial community succession using molecular techniques.
• Analysis of microbial community metrics, including abundance, diversity (alpha diversity), and structure.

Main Results:

• Low-dose biocide treatments (100 ppm) failed to control souring beyond 7 days, irrespective of biocide type.
• Sustained souring control for one year was only achieved with ARB at a high dose (750 ppm).
• High-dose biocide treatments significantly reduced microbial and SRM abundance (by one order of magnitude) and altered community structure.
• Recurrence of souring correlated with reduced alpha diversity and long-term microbial community shifts.
• Spore-forming sulfate reducers (Desulfotomaculum, Desulfurispora) were enriched in GA-treated groups, posing challenges for future control strategies.

Conclusions:

• High-dose ARB treatment at 750 ppm provides effective long-term souring control, while low-dose treatments are insufficient.
• Monitoring microbial community dynamics, particularly diversity and structure changes, can serve as an early warning system for biocide treatment failure.
• The enrichment of spore-forming SRM after GA treatment necessitates the development of novel, long-lasting souring control strategies.