Microbial enhanced oil recovery is a tertiary recovery approach in which reservoir-dwelling microorganisms produce the gas, surfactant or polymer that moves oil that waterflooding has already left behind. It applies only where the reservoir temperature and salinity let the relevant organisms survive, where the remaining oil can be mobilised by reduced interfacial tension or improved conformance, and where nutrients can be delivered and the result monitored. In most fields it is a slow, incremental technique rather than a step change.
This note is written for production engineers and for the buyers evaluating a bio-based oilfield product against a conventional polymer flood. It sets out what the mechanism actually is, the reservoir conditions that decide whether it is worth screening at all, and how it compares with the alternatives you are probably also weighing.
Product referenced in this article
Bio-based Oilfield Additive for Viscosity Reduction and Wellbore Cleanup — application notes, specification table and document downloads for this range.
The mechanism, in the order it actually happens
In a waterflooded reservoir the microorganisms are already there. MEOR works by steering an existing population, or by adding organisms together with the nutrients they need. The first effect is usually gas: organisms metabolising residual hydrocarbons produce carbon dioxide, nitrogen or hydrogen, which swell the oil, lower its viscosity and reduce the pressure needed to displace it.
The second effect is surfactant. Several organisms produce glycolipids or lipopeptides that lower the interfacial tension between oil and water, and that is what releases oil held in place by capillary force rather than by pressure. The third is polymer. Extracellular polysaccharide raises the viscosity of the water phase, which slows the fastest path through the reservoir and pushes water into rock that had been bypassed.
The fourth effect is the least obvious and often the most valuable: biomass and biofilm. A growing population occupies pore throats, plugs the most permeable channels and diverts flow into unswept layers. This is a conformance effect that no amount of additional water would have achieved on its own, and it is also the effect most likely to cause trouble in the wrong place.
The reservoir conditions that decide whether MEOR is worth screening
Temperature comes first, because it is the hardest limit. The organisms used in oilfield work are drawn from mesophilic and moderately thermophilic cultures. As reservoir temperature rises the viable population narrows sharply, until the organisms that would normally be introduced become difficult or impossible to maintain. A reservoir hot enough to suppress the target organisms is not a candidate, whatever the reserve figures say.
Salinity is the second. Seawater salinity is manageable for a number of halotolerant strains, but there is a limit, and there is a further complication in formations where the brine carries sulphate. Sulphate-reducing bacteria are already established in most waterflooded reservoirs, and an intervention that deliberately increases overall microbial activity gives them more room to work. Reservoir souring is covered in our separate note on microbial corrosion in oil and gas systems, and it belongs in the screening rather than in the post-mortem.
The third factor is the oil itself. Light and medium crude oils respond more readily than heavy oils, and heavy oils need more than one mechanism at once. Waxy and asphaltenic crudes complicate the picture further, because fouling risk rises and the surfactant has more to contend with in the pore throats.
The fourth factor is whether nutrients can be delivered and the result can be monitored. MEOR programmes usually run through an existing waterflood, which is an advantage, because it provides both a distribution route and a sampling programme. Where there is no waterflood, or where reinjection is impossible, the logistics of supplying nitrogen and phosphorus in a controlled way become the limiting factor rather than the biology.
How MEOR compares with polymer flooding
Polymer flooding is the benchmark, and it is a benchmark in a different sense: its behaviour is predictable because you know what you inject. The polymer is a manufactured product with a known concentration, and the response in the reservoir follows from how it interacts with the rock and the brine. Its weaknesses are well documented, among them adsorption onto the formation, shear degradation in the injection equipment and the injectivity decline that follows from it.
MEOR trades predictability for flexibility and a lower chemical cost. There is no single product to meter at the pump; there is a population, a nutrient regime and a monitoring obligation. Where the reservoir is well understood and a synthetic polymer would perform acceptably, polymer flooding remains the more defensible choice. MEOR earns its place where the formation is heterogeneous enough that mobility control is needed selectively, where polymer adsorption and retention would be severe, or where a microbial route fits a waterflood and biocide programme that already exists.
| Approach | What is injected | Main driver | Main limitation |
|---|---|---|---|
| Polymer flooding | A manufactured polymer | Mobility control at a known concentration | Adsorption, shear degradation, injectivity decline |
| MEOR | Nutrients and organisms, sometimes with a surfactant | A growing population that changes the flow pattern | Slow response, temperature and salinity limits, monitoring load |
| Both | Water | Conformance and displacement | Both require a functioning waterflood |
Where our products sit in a MEOR programme
Our bio-based oilfield additive is the general option, covering the microbial side of the problem, so gas production, surfactant production and polymer production can be addressed as one programme rather than three separate products.
If the mechanism you are relying on is surfactant, our rhamnolipid biosurfactant delivers the interfacial tension reduction without waiting for a population to establish. If it is mobility control, the BK Bio Gum microbial polysaccharide thickener supplies the viscosity increase directly. Each is a defined product with a defined application, and each can be used alongside a biological programme or instead of one.
Products in this family are specified against reservoir data rather than bought off a shelf; the selection criteria are set out in our guide to deciding whether bio-based oilfield additives fit your well.
What we do not promise
MEOR is routinely oversold, and the overselling is usually about speed. Microbial processes in a reservoir are slow. The population has to establish, the nutrient regime has to be tuned, and the flow redistribution shows up in the production history gradually. Anyone quoting a step-change uplift from a single treatment is describing something that does not happen reliably.
It is also incremental. A realistic expectation is improved recovery at the margin and better conformance, not a transformation of the asset. It does not replace waterflood management, and it does not remove the need for conformance control.
We are a National High-Tech Enterprise with 10+ granted patents and run our own fermentation pilot plant, so a blend can be reviewed against your data rather than taken from a catalogue. We are ISO9001, ISO14001 and ISO45001 certified, with a certificate of analysis per batch. We do not quote an uplift percentage or a fixed timeline, because both vary more between reservoirs than any product attribute can cover.
How to judge whether it is working
Monitor what moves first. Produced water chemistry and produced gas composition change before the oil rate does. A shift in the gas-oil ratio, a change in the water cut pattern, and the appearance or disappearance of specific compounds in the gas all tell you the population is active before the production history does.
On the injection side, track the nutrient balance, the injection rate and the pressure response. A well that takes injectant more readily after a period of dosing is telling you something about conformance. If nothing moves at all, with no gas change, no chemistry change and no pressure response, the population is not establishing and the programme should be reviewed rather than extended.
Keep a control where you can. Comparisons against an offset pattern or a group of neighbouring wells tell you more than a before-and-after comparison on one well, because reservoirs are not static and the oil rate moves for reasons unrelated to the programme.
What to send us for a screening opinion
Send the reservoir temperature at the target interval, the salinity and brine composition including sulphate, the oil type with its viscosity and composition, the permeability and completion configuration, the current waterflood or injection scheme, and the nutrients available for delivery. Add what has already been tried and what went wrong.
Our technical team replies with a screening view: whether the temperature and salinity envelope admits the organisms you would need, which mechanism the oil and rock support, what a nutrient and monitoring programme would look like, and where a chemical route would be more defensible.
Frequently asked questions
- What is microbial enhanced oil recovery?
- Microbial enhanced oil recovery is a tertiary approach in which reservoir-dwelling microorganisms produce the gas, surfactant or polymer that moves oil waterflooding has left behind. Gas lowers oil viscosity, surfactants reduce the interfacial tension holding residual oil in place, and extracellular polymer slows the fastest flow path through the reservoir. It is a route to incremental recovery, not a replacement for the waterflood it rides on.
- How long does it take for MEOR to show a response?
- Longer than most buyers expect, and that is the most common disappointment. The population has to establish, the nutrient regime has to be tuned, and the flow redistribution shows up in the production history gradually rather than as a step. We do not quote a fixed timeline, because it varies more between reservoirs than any product attribute can cover, and it depends on temperature, on distribution, and on whether the target interval is actually being swept.
- Is MEOR better than polymer flooding?
- Not in the general case. Polymer flooding is predictable, because you know what you are injecting and can meter it at the pump, and it is a mature technique with a large body of field experience behind it. Its known weaknesses are adsorption onto the formation, shear degradation and injectivity decline. MEOR trades that predictability for flexibility and a lower chemical cost, and earns its place where the formation is heterogeneous enough to need selective conformance, where polymer retention would be severe, or where a waterflood and biocide programme already carries the distribution.
- What reservoir temperature and salinity allow microbial activity?
- Temperature is the first and hardest limit. The organisms used in oilfield work come from mesophilic and moderately thermophilic cultures, and as temperature rises the viable population narrows sharply until the target organisms become hard to maintain. Salinity is the second: seawater salinity is manageable for a number of halotolerant strains, but there is a limit beyond which the population does not perform. These are the first two screening questions, and a reservoir that fails them is not a candidate whatever the reserve figures suggest.
- Does MEOR risk souring the reservoir or corroding steel?
- It deserves the question, and the risk has to be assessed during screening rather than discovered afterwards. Sulphate-reducing bacteria are already established in most waterflooded reservoirs, and an intervention that deliberately increases microbial activity gives them more room to work. Souring and microbiologically influenced corrosion are covered in our note on microbial corrosion in oil and gas systems, and any MEOR programme should be designed with the monitoring both require.
- What information do you need to assess an MEOR opportunity?
- Reservoir temperature at the target interval, the salinity and brine composition including sulphate, the oil type with its viscosity, the permeability and completion configuration, the current injection scheme, and what nutrients are available for delivery. Add what has already been tried. Our technical team replies with a screening view: whether the temperature and salinity envelope admits the organisms you would need, which mechanism the oil and rock support, what a nutrient and monitoring programme would look like, and where a chemical route would be more defensible.