Microbiologically Influenced Corrosion and Souring Control under Low and/or High Temperature Conditions.

Oil reservoir souring is a process through which sulfate-reducing microorganisms (SRM) produce sulfide, a toxic chemical responsible for endangering human and animal health, and causing environmental harm, corrosion of oilfield infrastructure, and devaluation of petroleum quality. Many souring control strategies have been studied, but bioaugmentation of a reservoir via nitrate reducing microorganism (NRM) culture injection along with nitrate is an understudied option that could provide souring control with fewer disadvantages compared to alternative treatments. Here, NRM injection was tested on simulated reservoir sand-packed sour columns at mesophilic and higher temperatures, with effective souring control after administration of a 30 mM (1920 ppm) nitrate NRM-containing treatment. 16S rRNA gene sequencing showed a shift to columns being dominated by NRM, while qPCR analysis showed sulfate-reduction-associated gene (aprA) copies decreasing and nitrate-reduction-associated gene (narG) copies increasing with successful NRM treatment of souring. While microbial sulfide production is linked to microbiologically influenced corrosion (MIC), some microbes are capable of the more corrosive process of electrical MIC (EMIC), where electrons are sourced from metal surfaces by direct contact or soluble redox mediators, causing severe corrosion. Here, oilfield enrichments under thermophilic conditions were evaluated for their EMIC capabilities by determining corrosion rates via weight loss and electrochemical techniques. Two thermophilic SRM cultures were found to be highly corrosive via electrochemical measurements in the absence of an electron other that carbon steel, suggesting their potential to carry out EMIC. These results contribute to knowledge of souring control and MIC under higher temperatures that characterize many oilfield operations.