Retention on cuttings (ROC) is the mass of fluid clinging to discharged solids after the separation train has done its work. On a non-aqueous well it is the number that decides whether cuttings can be legally discharged or must be treated, re-injected or hauled. On any well it is the direct measure of fluid lost with the discard — money leaving on the back of every pound of cuttings.
The method used in the field and required by regulators is the gravimetric wet/dry method — a straightforward mass measurement anchored to API RP 13C and, on the regulatory side, to EPA 40 CFR 435.
What ROC measures
10% means that for every 100 g of dry solids discharged, the cuttings carry 10 g of fluid with them.
The procedure
- Collect fresh cuttings from the shaker discharge or dryer underflow immediately.
- Weigh the wet sample at once — delay causes drainage or evaporation.
- Dry to constant mass at 105 °C until successive weighings agree within 0.1%.
- Weigh the dried sample and calculate ROC.
The regulatory link
The gravimetric wet/dry method implements the measurement required under EPA effluent guidelines for offshore oil-and-gas (40 CFR Part 435). For SBF cuttings discharged offshore in US waters, the regulatory limit on base fluid retained on cuttings drives directly from this number.
What the numbers mean
| ROC / OOC result | What it tells you | Next step |
|---|---|---|
| Below 3–5% (OBM/SBM) | VCD performing well | Continue monitoring |
| 5–10% | Dryer underperforming | Inspect screen basket, check feed rate |
| Above 10% | Significant fluid loss; likely compliance issue | Stop-check dryer; consider thermal treatment |
Key takeaways
Collect fresh, weigh immediately, dry to constant mass. The result is both a compliance gate and a real-time read on how much base fluid is leaving on the cuttings. The difference between 4% and 12% OOC is usually a worn dryer screen and an unmonitored feed rate.