Microbiologically influenced corrosion has been attributed to the activity of sulfate reducing and acid producing bacteria. Advances in DNA isolation and sequencing have revealed that these classes of bacteria often represent only a small portion of the corrosive microbial population present in the oil and gas environment.
We have identified a class of inhibitory molecules that abrogate sulfidogenesis in oilfield produced fluids. Bottle tests and laboratory-scale bioreactors to mimic field conditions, found that very low doses of two versions of this class of compounds were found to effectively prevent H2S generation.
By far, the microbiological species most associated with corrosion has been Sulphate-Reducing Bacteria (SRB). Majority of Microbiologically Influenced Corrosion (MIC) research has focused on the activities of this type of bacteria. One of the primary reasons for this has been the presence of iron sulfides in corrosion products associated with MIC. SRB reduce sulfates to sulfides, which then react with iron and steel. However, an accepted fact is that MIC is also caused by the action of the biofilm produced by bacteria, in a similar way to under-deposit corrosion.
The primary method used to prevent MIC in the oil and gas industry is by use of biocides. The criteria used for selection of biocides is often their proficiency to kill SRB. The danger with this is that one can neglect the ability of other bacteria frequently found in oil and gas environment, such as general aerobes and general anaerobes to cause corrosion by biofilm production. This became evident when severe general & pitting corrosion was observed in two oil and gas separators in one of the facilities in Kuwait Oil Company (KOC), where SRB levels were zero but significant numbers of sessile and planktonic general aerobes and general anaerobes were found to be present in the process.
Using microbiological and chemical analysis, the mechanism of this type of MIC, specially the relationship between the quantity of various biofilm-forming bacteria and nature and magnitude of corrosion has been studied and the findings are presented in this paper.
Microbial contamination is a major concern in oil/gas system or industrial water operation where it can result in multiple major corrosion issues and efficiency losses. Chemical treatment is the primary means to control microbial contamination, but due to changes in temperature and water sources, this results in major shifts in the microbial levels and populations which can influence the efficacy of these treatments.
Due to the shifts in the number of bacteria and the change in the dominant microbial species, optimal dosage of biocide is very difficult. Inadequate dosage regimen will result in major losses, whilst excess chemical dosage will incur unnecessary costs whilst also increasing the environmental load. A quick, reliable microbial measurement will help identify critical control points in the process and will allow optimization of dosing of the treatment program.
Agar growth, ATP, and media bottle testing have long been the standard for microbial detection, but these can lack the specificity, sensitivity and response time needed to adequately address the changing conditions in the industrial system described. The molecular-based approach, quantitative polymerase chain reaction (qPCR), described in this article, provides a near real-time method to measure bioburden, allowing operational decisions to mitigate issues to occur more rapidly.