A bottle test is the small-scale screening that decides which demulsifier a field will run. Candidate chemicals are dosed into fresh emulsion samples in graduated bottles, held at the temperature the field actually treats at, and ranked on how fast and how cleanly the water separates. It is at once the demonstration, the selection method, and — when a new product beats the incumbent — the switching decision. This page sets out a defensible procedure and gives a data-reporting template you can reuse, written with Niger-Delta conditions in mind: waxy, low-asphaltene crude treated at low temperature.
Demulsifier performance is specific to a crude, its water, and the conditions on the station — so it cannot be chosen from a datasheet. The bottle test reproduces the separation in miniature so several products, and blends of them, can be compared side by side against the current chemical on the same emulsion. The output is a ranked shortlist; the top one or two then go to a supervised field trial before any supply decision.
Take the sample from the point the treatment actually acts on — usually upstream of, or at, the inlet to the separation train (wellhead, manifold, or the free-water knockout inlet), not from a settled tank. Emulsions age: the interfacial film stiffens over hours to days, so a sample tested stale behaves differently from live production. Test as soon as practical, keep the sample near its production temperature in transit, and record the water cut and the exact sample point.
Where artificial lift or a choke has put the fluid through high shear (electric submersible pumps, gas lift, control valves), the water is dispersed into finer droplets and the emulsion is tighter. A sample taken after that shear represents the real treating problem; a gently handled sample can look easier than the field is.
Fill a row of graduated bottles (100 mL is standard) with equal, well-mixed volumes of the same emulsion. Reserve one as a blank with no chemical — it shows how much water, if any, drops on its own and is the baseline every product is judged against. Dose the remaining bottles across a ladder that brackets the expected field rate — for example 10, 25, 50, and 100 ppm — using a micro-syringe to add the small volumes involved. Run each candidate product across the same ladder so products are compared at equal dose.
Dose in parts per million of the total produced fluid. Optimized field rates commonly land in the 10–50 ppm range, though the useful screening window is wider; the test finds the rate, so bracket it rather than assume it.
Cap the bottles and agitate them the same way — a fixed number of inversions or shakes — so mixing energy is equal across the row; uneven mixing, not chemistry, is a common source of misleading results. Then place them in a water bath at the temperature the field treats at. This is the single most important setting for Niger-Delta work: measured effluent temperatures at some onshore stations are only around 36–40 °C, well below the 60 °C often used as a warm laboratory default. A product that wins at 60 °C can fail at 40 °C, because the wax that helps stabilize the emulsion is still crystallizing at the lower temperature. Test cold if the field runs cold.
Record four things, on a timed schedule (for example at 5, 10, 15, 30, 60, and 120 minutes):
| Reading | How to judge it | Good result |
|---|---|---|
| Water drop | Volume of free water fallen out, read off the graduations, at each time point | Fast, and reaching the full water cut |
| Interface | The oil–water boundary: sharp and level, or a loose, feathery band | Sharp and flat — no thick transition band |
| Water quality | Clarity of the dropped water: clear, hazy, or dirty with carried-over oil | Clear — little oil left in the water |
| Rag layer | Any stable emulsion pad sitting at the interface | None, or thin and collapsing |
The final check is residual BS&W in the treated oil — basic sediment and water — which is what the crude is actually sold against. A small spun-down sample (a field centrifuge) gives it. A product can drop water quickly and still leave the oil off-spec, so read the top phase, not just the water volume.
Rank the candidates on the readings above at each dose. Two failure modes matter as much as the winners. Underdosing leaves water undropped and the interface loose. Overdosing can re-stabilize the emulsion and build a rag layer — the fault that is most visible and most expensive in a real separator, and the one a new supplier is judged on hardest. The best product is the one that reaches clean separation at the lowest reliable dose, with a wide margin before overdosing begins to re-stabilize the emulsion.
Single products often do not win outright. It is standard to screen combinations — a primary demulsifier base plus, for a waxy low-asphaltene crude, a solids-wetting or paraffin-handling component — testing blends the same way across the dose ladder. The shortlist that goes to the field is usually a blend, not a ready-made single product.
The bottle winner is confirmed on the station, injected continuously at the chosen point and dose, with the operator watching interface level, water quality, and export BS&W over a set period. Published and tendered trial windows for this work commonly run from about two weeks to a month. The bottle test narrows the field cheaply; the trial proves it on real, continuously changing production.
Consistent recording is what makes one test comparable to the next and to a field trial later. Log every bottle on one sheet:
| Bottle | Product | Dose (ppm) | Water @30 min | Water @120 min | Interface | Water clarity | Rag | Residual BS&W |
|---|---|---|---|---|---|---|---|---|
| Blank | None | 0 | ||||||
| 1 | 10 | |||||||
| 2 | 25 | |||||||
| 3 | 50 | |||||||
| 4 | 100 |
Header the sheet with the fixed conditions — field and sample point, date and time drawn, water cut, test temperature, crude type, and the incumbent product as a reference bottle. Those conditions are why a result holds or does not, and they are the first thing a regulator’s or operator’s reviewer asks for.
Niger-Delta crudes are typically waxy and very low in asphaltene, and many onshore stations treat with little heat. Two consequences for the bottle: run it at the real treating temperature, not a warm lab default; and expect that a base chemistry designed for asphaltene-stabilized emulsions may underperform, because here the film is built more from wax crystals and fine solids. That gap is exactly why field-specific screening, not catalog selection, decides the winner.
This is a general method for comparing products, not a laboratory or regulatory standard. For an approval file in Nigeria, testing is done through a NUPRC-accredited laboratory; confirm the required protocol with the lab before you begin.