Corrosion risk associated with microbial souring control using nitrate or nitrite

Area of Science:

• Microbiology
• Corrosion Science
• Petroleum Engineering

Background:

• Souring, caused by sulfate-reducing bacteria (SRB), produces hydrogen sulfide in oil reservoirs.
• SRB activity leads to significant infrastructure corrosion.
• Nitrate and nitrite are potential inhibitors of SRB activity.

Purpose of the Study:

• To evaluate the impact of nitrate and nitrite addition on controlling souring.
• To assess the resulting effects on microbial corrosion rates and patterns.
• To determine the optimal strategy for corrosion prevention in oil reservoirs.

Main Methods:

• Metal coupons were placed in packed-bed bioreactors simulating oil reservoir conditions.
• Bioreactors were inoculated to induce biogenic hydrogen sulfide production.
• Treatments included nitrate (17.5 mM) and varying nitrite doses (up to 20 mM).
• Corrosion rates and patterns were analyzed under different treatment conditions.

Main Results:

• Untreated bioreactors showed high corrosion rates (up to 0.4 mm/year) near the outlet.
• Nitrate addition eliminated sulfide but caused pitting corrosion near the inlet.
• High-dose nitrite (20 mM) completely inhibited microbial activity and corrosion.
• Gradual nitrite addition retained microbial activity and caused localized pitting corrosion.

Conclusions:

• SRB control via nitrate/nitrite shifts corrosion from the outlet to the inlet.
• Continuous high-dose nitrite addition is the most effective strategy for corrosion prevention.
• Understanding these shifts is crucial for managing corrosion in production and injection wells.