An experimental study of microbiologically influenced corrosion (MIC) was conducted involving online, real-time monitoring of a biofilm loop under controlled conditions simulating oilfield water handling and injection. Biofilm growth, MIC and biocide efficacy were monitored using an automated, multi-technique monitoring system including linear polarization resistance, electrochemical noise and harmonic distortion analysis. This data was correlated with conventional off-line methods to differentiate conditions of varying MIC activity in real-time to facilitate quick assessment and operator intervention.
In a previous investigation, an evaluation of electrochemical techniques were conducted involving the use of linear polarization resistance (LPR), harmonic distortion analysis (HDA) and electrochemical noise (EN) for evaluation of microbiologically influenced corrosion (MIC) ? See Appendix I for a review of these techniques. These electrochemical techniques were used to study the corrosion of carbon steel due to the activity of sulfate reducing bacteria (SRB) in simulated seawater injection environments using North Sea water in a laboratory flow loop. The effects of SRB activity on the electrochemistry of the corroding interface and the effects of biocide treatments were examined. [1] While electrochemical monitoring provided certain advantages for detecting corrosion due to SRB activity and the effectiveness of biocide treatments, the capability to deliver a field-ready solution for online, real-time monitoring was not complete at the time of this previous investigation. However, this study provided an initial look at bacterial metabolic activity and the associated corrosion activity on carbon steel as determined by multiple electrochemical corrosion monitoring techniques. In these experiments, (It is difficult to tell if there were several previous experiments or investigation or just one.) it was shown that SRB activity resulted in the corrosion of carbon steel, primarily due to the formation of hydrogen sulfide.
Currently, in sea-water injection systems, bacterial activity is usually monitored by biological sampling involving everything from a variety of quick checks to culturing techniques to define the presence and activity of SRB populations. Furthermore, these methods do provide critical information such as biofilm community composition and specific populations numbers. The biological activity of SRB?s can usually be controlled using several methods. The application of biocides is the most widely accepted method used to control bacterial activity. Another method that is gaining acceptance is the application of nitrate which stimulates the growth of nitrate reducing bacteria which reduces the activity of SRBs. However, if the improper biocide is used or inadequate concentrations of either biocides or nitrate are applied, SRB activity may persist resulting in catastrophic corrosion of water injection system piping and facilities. Thus to respond to bacterial activity in a manner that would prevent or reduce MIC, there exists a need for immediate monitoring of bacterial activity so an appropriate response can be implemented.
Electrochemical corrosion monitoring techniques have the ability to provide real-time monitoring to address the needs of operators of field facilities to control bacterial activity. Although quick checks and culturing techniques are critical to fully understand that the microbiological component of corrosion, they are generally time consuming manual processes that are not easily amenable to the online, real-time needs of operators. Electrochemical corrosion monitoring techniques provide the distinct advantage of a quick response time
