Lecture 15 Flashcards
Biofilms are surface attached microbial communities encased in EPSs.
What are some examples of EPSs?
EPS: Extracellular polymeric substances
- Polysaccharides
- proteins
- nucleic acids
- lipids
- inorganic particles from the fluid phase
- water
- corrosion products
What do non uniformly distributed biofilms do for microbes?
They provide protection from the outside environment and access to energy sources.
In a pipeline biofilm with an organized consortium where are the anaerobic and aerobic microbes going to be located?
aerobic on top, anaerobic near the metal.
between general and pitting corrosion, which is the better indicator of MIC?
pitting corrosion
Compare Chemical MIC to Electrical MIC.
Indirect or CMIC is when a metabolite of a microbe is a corrosive product. e.g., sulfide will react with Fe2+ to form FeS.
Direct or EMIC is when the microbes take up electrons from a metal electron donor itself.
What overall reaction did cathodic depolarization theory propose?
pg 5
When will FeS passivate/ protect metal from corrosion?
When it is in a uniform layer. A non-uniform layer will accelerate corrosion.
What are three mechanisms of EMIC?
- Direct Iron-to-Microbe electron transfer (DIMET)
- H2-mediated Iron-to-microbe electron transfer (HIMET)
- Shuttle-Mediated Iron-to-microbe electron transfer.
which method, CMIC or EMIC, usually has a faster corrosion rate?
- EMIC has an average corrosion rate of 0.9mm/ year
- CMIC has an average corrosion rate of 0.4mm/ year
What are the three lines of evidence required to diagnose MIC?
- Microbiological
- Chemical
- Metallurgical
What needs to occur during sampling and sample preservation of both sessile and planktonic samples?
- Sterile vessels and sampling tools
- Preservation of genomics analysis
- Maintenance of anaerobic conditions
- Rapid shipping times
What is the most common approach to measuring oilfield microbes? What are some of its limitations?
Culture based “bug bottles” (BART and MPNs)
targets <1% of microbes in a sample. Usually only measures planktonic cells rather than sessile cells.
what kind of chemical measurements are taken when trying to measure particular microbes?
- Compounds (VFAs, acetate, propionate, butyrate are good at detecting APB)
- Salinity
- pH
- Sulfate, nitrate, nitrite, sulfide, total Fe, NH4+
- composition of corrosion products.
List three corrosion products which can be measured to allow us to understand corrosion in a particular system?
- FeS - severe overlapping pits (MIC)
- Fe2<Osub>3</sub> - classic rust pitting</Osub>
- FeCO3 - benign general anaerobic corrosion
pg 5
What is a sign of microbial corrosion during a metallurgic analysis?
While some corrosion will occur through abiotic means, microbes will tend to make small, bacteria-shaped pits in the metal. This can be identified with light or SEM microscopy.
