Simulation of sour-oxic-nitrite chemical environment in oil and gas facilities

The nature of the chemical environment in oil and gas fluids such as produced water (PW) and soured oil or low-oxygen environments plays a vital role in microbiologically influenced corrosion (MIC). H2S and/or other forms of sulphur species in soured oils and PW are key factors in the corrosion and growth of microorganisms. To mitigate reservoir souring and subsequent corrosion, nitrate is injected to displace sulphate-reducing bacteria with nitrate reducers. However, nitrates and the associated nitrogen species (eg, nitrite) impact the chemistry and microbial activity, and hence the corrosion potential in the system. This study investigates the PW chemical environment in light of sulphide and nitrite chemistry, and provides information towards understanding the chemical transformations and microbial relationships. The sulphide-nitrite environment was studied as a function of temperature, pressure, nitrite level, oxygen-using equilibrium, and kinetic model approaches. Equilibrium simulation predicted the formation of FeS, FeO(OH), and Fe2O3 as the key corrosion products, the amount of which varied depending on the chemistry and operating conditions. In experiments where nitrite was very low or absent, S-0 was favoured over SO42- as the inlet H2S concentration increased and FeS dominated with an increase in temperature. In the presence of nitrite, Fe2O3 was formed instead of FeO(OH) at temperatures above 50 degrees C. The trend of the kinetic simulation of the sulphide-oxygen reaction in seawater was in good agreement with the wet-lab experiment in PW. The models can serve as tools to better understand and describe the chemical environment in PW systems.

Automated summary

The nature of the chemical environment in oil and gas fluids, such as produced water and soured oil, plays a crucial role in microbiologically influenced corrosion. The study investigates the effects of sulphide and nitrite chemistry on the corrosion potential and microbial relationships within the system. Equilibrium and kinetic models provide insights into the formation of corrosion products and the impact of nitrate on the system's chemistry and microbial activity.