Microbial corrosion in oil and gas is driven mostly by sulphate-reducing bacteria that live in biofilms on metal surfaces and create localised, low-pH cells that pit steel. It is managed rather than eliminated: by controlling the biofilm and the sulphate source, by measuring corrosion rates with coupons and probes, and by treating any deliberate bio-based programme as part of the same surveillance activity that tracks souring and corrosion.
Product referenced in this article
Bio-based Oilfield Additive — application notes, specification table and document downloads for this range.
What microbial corrosion actually is
Most corrosion attributed to microbes is the work of sulphate-reducing bacteria, or SRB, that colonise the biofilm on a metal surface. In the low-oxygen pocket a biofilm creates, SRB use sulphate as an electron acceptor and, in doing so, remove the protective film that would otherwise slow corrosion. The result is not uniform thinning but localised pitting, and pitting is the expensive kind: a pipe can look sound on the outside and fail suddenly at a pit.
This is why the term microbially influenced corrosion, or MIC, is used rather than simply microbial corrosion. The organisms rarely corrode metal directly; they change the local chemistry — oxygen, pH, sulphide — in ways that accelerate the electrochemistry already present. Understanding that the biofilm is the environment, not just a coating, matters for every control option that follows.
Where it shows up in oil and gas
The same mechanism appears across the asset. In water injection systems, SRB grow in the water leg and seed the whole network, so a single contaminated source can distribute the problem field-wide. In pipelines carrying water and hydrocarbon together, the water phase at the bottom is where biofilms establish. Topside, stagnant equipment and temporary lay-up are common sites. And in the reservoir itself, SRB sour the oil by generating hydrogen sulphide, which then corrodes the steel it contacts and creates a safety hazard on top of a materials one.
Because the reservoir and the surface system share the same microbiology, a change made downhole — including a deliberate bio-based programme — moves the surface corrosion and souring risk at the same time. That coupling is the single most overlooked point in oilfield corrosion management.
Why it costs more than it looks
Pitting fails equipment before wall-loss calculations predict, which means inspections scheduled against uniform corrosion miss it. The consequence is unplanned downtime and, where hydrogen sulphide is involved, a toxic-gas exposure path that has to be engineered around rather than merely monitored. The cost is therefore rarely the metal itself; it is the failure mode being unpredictable and, in sour service, dangerous.
This is also why a treatment that only reduces the average corrosion rate can still fail to prevent failures, if the localised pitting mechanism is left running. The objective of any control programme is to act on the biofilm and the sulphate source, not only on a bulk number.
How it is actually monitored
Corrosion is measured where it happens. Coupons left in the stream give a direct, if slow, rate and a visible pitting record. Electrical-resistance and linear-polarisation probes give a faster, continuous signal but a less physical one. Biofilm and sessile-bacteria sampling answers a different question — whether the organisms driving the mechanism are present — which a metal coupon alone cannot tell you.
For MIC specifically, the useful programme combines a metal-loss signal with a microbiology signal and treats them as one dataset. A rising corrosion rate with a rising SRB count is a different problem from a rising corrosion rate with a falling count, and the two call for different responses. The monitoring has to be designed before the treatment, not added afterwards.
Control options and their limits
Biocides — oxidising and non-oxidizing — are the standard first response, and they work when the biofilm is reachable and the dose is sustained. Their limit is that biofilms protect the organisms inside them, so a programme that only nudges the bulk count leaves the pitting site intact, and repeated dosing builds both cost and resistance. Mechanical and chemical cleaning reaches the surface directly but does not keep it clear.
Bio-based options are best understood as part of the same programme rather than a replacement for it. A biological additive that changes the population also changes the conditions for SRB, which is why it must be run with the corrosion and souring monitoring described above rather than as a standalone product. Our broader note on deciding whether bio-based oilfield additives fit your well covers the screening question, and the same monitoring discipline applies here.
A short checklist
- Is the failure pitting or uniform loss — and is the local chemistry being measured?
- Where is the water phase, and is the injection source screened for SRB?
- Are metal-loss probes and biofilm sampling run as one dataset?
- Does any bio-based programme include souring and corrosion surveillance by design?
- Is hydrogen sulphide present, and is the safety case built around it?
Frequently asked questions
- What is the difference between MIC and ordinary corrosion?
- Ordinary corrosion is an electrochemical reaction between metal and its environment. Microbially influenced corrosion is that same reaction accelerated and localised by a biofilm, most often driven by sulphate-reducing bacteria that change the local oxygen, pH and sulphide conditions at the metal surface. The practical difference is that MIC produces pitting rather than uniform loss, so it fails equipment sooner than a wall-loss calculation predicts.
- Can biocides alone solve microbial corrosion?
- Biocides reduce the bulk bacterial population and are the standard response, but a biofilm shields the organisms within it, so dosing that only lowers a bulk count can leave the pitting site active. Repeated or rising dosing also builds cost and can select for resistance. They are most effective as part of a programme that also measures the biofilm and the corrosion rate, rather than as a standalone fix.
- How does a bio-based oilfield additive relate to corrosion?
- Because oilfield microbiology couples the reservoir and the surface system, a deliberate bio-based additive changes the same population that drives souring and corrosion. It should therefore be run inside the corrosion and souring surveillance programme, not as a separate product, so that any shift in the microbial environment is measured rather than assumed.
- What should be monitored before treating microbial corrosion?
- Combine a metal-loss signal — coupons and electrical-resistance or polarisation probes — with biofilm and sessile-bacteria sampling, and treat them as one dataset. Whether hydrogen sulphide is present also has to be established up front, because sour service changes both the failure mode and the safety case. Monitoring designed before treatment is what lets a control programme show it worked against a baseline.