Novel MIC Mitigation Strategies and Improved Microbiological Monitoring Techniques

Abstract

Novel MIC Mitigation Strategies and Improved Microbiological Monitoring Techniques

Microbial induced or influenced corrosion (MIC) is estimated to result in billions of dollars of damage annually to world-wide oil and gas facilities. Although much work has been conducted identifying the principal bacteria involved in MIC, the importance of the role of archaea, e.g. sulfate-reducing archaea and methanogens in MIC, has only recently been understood. Little work has been carried out investigating the efficacy of traditional MIC mitigation strategies such as biocide application on archaea; however it is possible that archaea will be more resistant to biocidal action due to the very different biochemical composition of the cell wall and membrane seen in archaea.

A well managed biocide regime can greatly reduce the risk of MIC and maintain facilities integrity; however conventional biocides have drawbacks in that they are both highly toxic and harmful to the environment. With many governments introducing tougher legislation for discharge of waste water to the environment, there is increasing interest amongst oil and gas companies for more environmentally-friendly biocides.

One example of a ‘green biocide’ that has shown promise is nitric oxide. Nitric oxide is naturally generated by mature biofilms to stimulate dispersal of cells from the biofilm to colonize other locations. By application of exogenous nitric oxide via donor molecules, dispersal of mature biofilms can be induced. Application of nitric oxide at the attachment phase can minimize biofilm formation. Nitric oxide alone has been shown to remove 60% of a mature biofilm and acts synergistically in the presence of biocides, leading to enhanced biofilm removal. Furthermore, nitric oxide initiates the dispersal of biofilms at very low concentrations and has been shown to be effective against a broad range of micro-organisms. A second example of a ‘green’ biocide is modified chitosan. Chitosan, a deacetylated derivative of chitin, itself a constituent of crustacean shells, is a low-toxicity, biodegradable, antimicrobial polymer. Chemical modifications can produce a range of modified chitosan molecules with enhanced antimicrobial and surfactant properties. The potential use of nitric oxide and modified chitosan for MIC control will be discussed, but noting that these techniques need further developing and field trials.

Finally, the drawbacks of conventional microbiological monitoring using culture-based techniques are well known. Molecular microbiological based techniques are now ubiquitous in other industries but have yet to be fully integrated into the oil and gas industry. Novel monitoring techniques that have been shown to be robust, for use on-site will be discussed. The technologies should be quick, easy and add real value by allowing informed decisions to be made regarding issues such as biocide use, but again need extensive field trials.