Implications of Limited Thermophilicity of Nitrite Reduction for Control of Sulfide Production in Oil Reservoirs

What is it about?

Nitrate is injected into high temperature oil reservoirs to prevent sulfide formation (souring) by sulfate-reducing bacteria, which are strongly inhibited by nitrite. However, injection of cold seawaters creates mesothermic zones where nitrate is reduced through denitrification to N2 or through dissimilatory nitrate reduction to ammonium, causing inhibition of sulfate reduction by nitrite to be only transient. We found that thermophilic nitrate reducers reduce nitrate to nitrite, but that nitrite was not reduced further at and above 50oC. As a result, souring could be controlled with a low concentration of nitrate injection in high temperature oil reservoirs.

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Why is it important?

The performance of nitrate as a souring control agent could be improved if the temperature of any part of the near injection wellbore region is not allowed to drop below 50oC. This can be achieved by reinjection of hot produced water, which is not yet commonly done in offshore seawater flooded reservoirs.