Quick answer: Emulsion stability is tested mainly by the bottle test — measured volumes of emulsion are dosed with candidate demulsifiers at set concentrations, held at process temperature, and watched over time for how much water drops out, how fast, how clean the interface is, and how bright the oil becomes. Centrifuge and water-drop tests give faster, quantitative BS&W-style readings, and simple conductivity checks confirm the emulsion type. Field screening does a rapid version at the wellsite; the lab does the controlled, comparative version. The results rank demulsifiers and set the dose before anything is deployed to the process.
Key figures at a glance
- Primary method: the bottle test (dose, mix, hold at process temperature, time water drop)
- Judged on: water drop rate, interface sharpness, oil brightness, water clarity
- Supporting tests: centrifuge test and water-drop (grind-out) for quantitative BS&W
- Samples: use freshest representative sample — emulsions age and stiffen
- Outcome: ranked demulsifiers and the minimum effective dose
Before you treat an emulsion you have to test it — both to confirm what you are dealing with and to choose the chemistry that will break it. This guide covers the test methods, distinct from the stability page that explains the factors that make emulsions stable. The bottle test is the workhorse, so most of this focuses there.
Why stability testing matters before treatment
Demulsifiers are crude-specific — a product that breaks one emulsion may do nothing to another. Testing stability and screening candidate chemistries first avoids deploying the wrong product at the wrong dose, which wastes chemical and can even stabilise the emulsion further. Testing turns treatment from guesswork into a ranked, evidence-based selection, and it establishes the baseline against which field performance is judged.
The bottle test step by step
The bottle test is the standard screening method:
- Sample fresh, representative emulsion and split it into equal, measured volumes in graduated bottles (prewarmed to process temperature).
- Dose each bottle with a different candidate demulsifier, or the same product at different concentrations, keeping one undosed as a blank.
- Mix consistently — a set number of shakes or a standard agitation — so every bottle sees the same energy.
- Hold at process temperature and record water drop-out volume at timed intervals (for example every few minutes, then longer).
- Assess the results: how much water dropped, how quickly, the sharpness and cleanliness of the interface, and the clarity/brightness of the separated oil and water.
The best demulsifier is the one that drops the most water fastest, leaves the cleanest interface, and produces bright oil and clear water at the lowest effective dose.
Centrifuge and water-drop tests
Complementary tests add speed and numbers. A centrifuge test spins a treated sample to force rapid separation and read a BS&W-style water-and-sediment figure — quick and quantitative. A water-drop (grind-out) test similarly quantifies water content. These are useful for fast comparison and for measuring the water still emulsified after treatment, alongside the visual bottle-test observations.
Field vs lab screening
There are two settings for the same logic. Field screening runs a rapid bottle test at the wellsite on the freshest possible sample to get a quick working answer and account for how the emulsion behaves right at source. Lab screening runs a controlled, comparative programme across many chemistries and doses under repeatable conditions, including ageing and temperature effects. Fresh field samples matter because emulsions age and change, so the two settings are complementary rather than alternatives.
Interpreting results and selecting a demulsifier
Reading the test is about more than water volume. Rank candidates on rate and completeness of water drop, interface quality (a sharp, clean interface with no rag layer beats a large but messy drop), and oil and water clarity (bright oil, clear water). Then confirm the minimum effective dose. The chosen product is the one that scores best across these together — which is why a purely numerical reading can mislead if the interface is dirty. This screening is a core part of laboratory support.
Reading a bottle test beyond the water drop
The volume of water dropped is only the headline result of a bottle test; the quality of the separation tells you which demulsifier will actually perform in the plant. A product that drops a lot of water but leaves a fuzzy, slow-clearing interface or a hazy oil is usually worse in service than one that drops slightly less water but gives a sharp interface, bright oil, and clear water. The interface quality is the single most telling observation, because a messy interface in the bottle becomes a rag layer in the separator.
Timing matters too. Recording water drop at intervals — early and late — separates fast-acting products from slow ones, which is important when the process gives the emulsion only limited residence time. A demulsifier that eventually drops all the water but only after an hour is no use in a separator with ten minutes of residence.
Finally, the minimum effective dose is part of the reading: the best product is the one that achieves a sharp interface and clean fluids at the lowest dose, because over-dosing not only wastes chemical but can re-stabilise the emulsion or cause carry-over. Interpreting all of these together — rate, interface, clarity, and dose — is what makes bottle testing predictive rather than merely indicative.
From bottle test to field programme
A bottle test ranks demulsifiers under controlled conditions, but translating that result into a working field programme takes a few more steps that are easy to skip. The laboratory ranking identifies the best chemistry and an approximate dose, but the field applies it at real temperatures, real residence times, and real injection points, so the initial field dose is set from the bottle test and then trimmed against the actual separator performance — BS&W and interface quality — over the first days of application.
Injection location and mixing matter as much as the product: dosing just upstream of the separator leaves the demulsifier too little residence time to work at the interface, while good upstream injection with adequate mixing lets a lower dose work. The field programme also has to track change — as water cut rises or crude character shifts, the emulsion evolves and the programme is re-screened rather than assumed to hold.
This is why laboratory screening and field optimisation are two halves of one process. The bottle test prevents deploying the wrong chemistry; the field trim gets the dose and injection right for the plant; and periodic re-testing keeps both matched to a changing fluid.
Frequently asked questions
How do you test emulsion stability?
Mainly with a bottle test: dose measured volumes of emulsion with candidate demulsifiers, hold at process temperature, and record how much water drops out, how fast, how clean the interface is, and how bright the oil becomes. Centrifuge and water-drop tests add fast quantitative readings.
What is a bottle test for demulsifiers?
It is a screening method where identical samples of an emulsion are dosed with different demulsifiers or doses, mixed the same way, and observed over time. The product that drops the most water fastest with the cleanest interface and clearest fluids at the lowest dose is selected.
Should emulsion samples be fresh?
Yes. Emulsions age and their films strengthen over time, so testing the freshest possible representative sample — ideally with a field screen at source plus controlled lab work — gives results that reflect how the emulsion actually behaves in the process.
Related Rodanco resources: See Rodanco’s water-in-oil emulsions overview and laboratory expertise page for bottle-test and screening support.
Where Rodanco fits: Rodanco runs bottle-test and laboratory screening to rank demulsifiers and set doses for your specific emulsion. See our Water-in-Oil Emulsions and Laboratory Expertise pages, or arrange testing through the Rodanco contact page.