Abstract
Microbially Influenced Corrosion is primarily caused by sessile microbes found within a biofilm. The ultimate goal of many biocide treatments is the removal of any biofilm within that system. These cells may be killed but remain in place, be removed but not killed, or may be both killed and removed. Many of the factors that determine the fate of sessile cells are poorly understood. For example, deciding to treat a system with a low dose of biocide for a long period of time or to treat with a high dose of biocide for a short period of time may yield drastically different results in terms of reducing the risk of microbially influenced corrosion. In this study, we show a comprehensive approach to growing in vitro biofilms to conduct sessile kill studies for product qualification.
Introduction
Microbiologically Influenced Corrosion (MIC) is a major cause of corrosion failures in oilfield production and water injection systems. Microbes thrive in the anaerobic conditions encountered in these systems and are supported by nutrients and metabolites found in produced water.
Some biocides possess surface active properties which make them more suitable to kill the free floating planktonic bacteria and facilitate penetration and removal of the biofilm from metal surfaces. A biocide’s ability to penetrate and loosen a biofilm is a key factor when selecting the correct chemistry to combat MIC for a particular application. Despite the importance of the characteristics described above, it is still rare for biocide decisions to be based off of credible techniques that accurately measure biocide performance. To gauge efficacy of a biocide in oilfield production systems, it is common practice to conduct a time kill study against planktonic bacteria using culture dependent methods (serial dilution). Kill studies aimed at sessile microbes are performed far less often despite the fact that the most serious issues posed by oilfield microbes are associated with biofilms. Previous research has established that it is substantially easier to kill planktonic microbes than microbes found in a biofilm ¹. For example, Costerton et al. have demonstrated that some species of bacteria are 500 to 5000 times less susceptible to biocide treatment in biofilm form than that same species of bacteria found in planktonic form ².
