Every barrel of oil a mature field produces comes up with water, and that water has to go somewhere — discharged to the environment or reinjected. Before it can be, the oil carried in it must be brought under a legal limit measured in milligrams of oil per litre of water (mg/L). In Nigeria the limit is tiered by where the water is discharged, it is stricter inland than offshore, and many stations currently miss it. This page explains the framework, the commonly cited numbers, and the honest uncertainty about which exact figures are current.
The controlled number is the concentration of oil and grease left in the produced water at the point it is discharged or reinjected — how much oil the water still carries after treatment. It is reported in mg/L. Other parameters travel with it in the regulations (salinity, total dissolved solids, chemical and biological oxygen demand, pH, temperature), but oil-in-water is the number that continuous chemical treatment and the separation train are trying to hit.
The framework comes from EGASPIN — the Environmental Guidelines and Standards for the Petroleum Industry in Nigeria — and sets the oil-and-grease limit by discharge location. The values most commonly cited from the published EGASPIN tables are:
| Discharge location | Oil & grease limit | Note |
|---|---|---|
| Inland waters | ~10 mg/L | The strictest tier — sensitive inland and shoreline waters (secondary-source figure). |
| Nearshore / continental shelf | ~20 mg/L | Intermediate tier (secondary-source figure; some tabulations cite ~30 mg/L). |
| Offshore / deep offshore | ~40 mg/L | The most consistently cited value — a monthly average, with a higher daily maximum around 72 mg/L. |
Treat these as the right order of magnitude and the right structure, not as final, confirmed figures. The most consistently cited single value is the offshore 40 mg/L monthly average with a ~72 mg/L daily maximum; the inland and nearshore tier values vary more between published tabulations — some cite the tiers as roughly 30 mg/L on the continental shelf and 40 mg/L deep offshore — and the exact boundaries depend on the specific water body. The reliable takeaways are the shape of the rule (tiered, stricter inland) and the scale (single tens of mg/L). For a compliance number you will act on, read it off the current regulation for your specific discharge point.
NUPRC — the current upstream regulator — administers produced-water discharge through the Upstream Petroleum Environmental Regulations 2022, which sit on top of the older EGASPIN framework that the former DPR issued. In practice operators still work to EGASPIN-style, location-tiered oil-in-water limits, and treatment chemicals must be approved through NUPRC (with toxicity testing at accredited laboratories).
The consolidated gazette text of the 2022 Regulations is not, at the time of writing, hosted at a stable public address, and the figures circulating in academic papers and secondary summaries do not perfectly agree. So we state the framework and the commonly-cited values, and we flag that whether the 2022 Regulations restated, tightened, or re-tiered the specific numbers is something to confirm directly with NUPRC or a NUPRC-accredited laboratory before you rely on a figure. We would rather mark the uncertainty than publish a precise number we cannot stand behind.
Field measurements tell the real story. Studies of Niger-Delta onshore flow stations and terminals have reported oil-and-grease in discharged water well above the applicable limits — figures in the range of roughly 40–80 mg/L have been published, which is several times over an inland or nearshore limit. Three things drive the gap:
| Cause | What happens |
|---|---|
| Rising water cut | Aging fields lift far more water per barrel of oil; the water-treatment load climbs even when oil output is flat, and undersized separation trains fall behind. |
| Low treating temperature and short residence time | Gravity separation needs time and, for tight droplets, heat; where both are short, fine oil droplets stay suspended and carry over into the water. |
| No, or the wrong, water-side chemistry | The oil-in-water emulsion in the water leg needs its own treatment — a reverse demulsifier or water clarifier — which is a different product from the crude-side demulsifier. If it is absent or mismatched, the water leaves dirty. |
The gap between the measured number and the legal one is the commercial opening for produced-water treatment: it is a compliance problem with a chemical answer, and it grows on its own as fields age.
Not the crude-side demulsifier. The water leaving the separators carries a dilute oil-in-water dispersion, and it is cleared with a reverse demulsifier or water clarifier — chemistry that neutralizes the charge holding the fine oil droplets apart and flocculates them so they float off or filter out, in a skim tank or flotation unit. The two jobs are usually tuned together, because the crude-side and water-side treatments act on the same separation train. The difference between them is the subject of a separate explainer.
Regulatory values on this page are compiled from published secondary sources and are presented as indicative, not as legal advice or a current official figure. Confirm the limit for your discharge point against the current NUPRC regulation before acting.