Non-aqueous drilling fluids (NADF) — OBM and SBM — change the solids-control job in fundamental ways. The equipment is mostly the same; the priorities, measurements and waste implications are not. A solids engineer who steps from a WBM job onto a NAF well without adjusting their thinking will measure the wrong thing, misread the dryer, and create a compliance problem without realising it.
The primary metric shifts from LGS to OOC
On WBM the number you manage is LGS. On NAF, oil-on-cuttings (OOC) takes equal or greater weight — it is simultaneously a fluid-cost metric and a compliance gate.
Equipment differences
| Stage | WBM | NAF (OBM/SBM) |
|---|---|---|
| Shaker | Standard | Oil-wet cuttings stickier; finer screens flood more easily |
| Drying stage | High-G shaker adequate | VCD needed to drive OOC below 5% |
| Centrifuge | LGS removal / barite recovery | Same duties, plus processes recovered base oil from dryer |
| Retort | API RP 13B-1 | API RP 13B-2; reads OWR — more involved to interpret |
Waste — the most different part
OBM cuttings are classified oily waste and typically cannot be discharged offshore without treatment. The cuttings dryer, CRI or thermal treatment are not optional enhancements — they are the waste management system. A NAF well without a functioning VCD generates non-compliant waste from the first bit run.
Key takeaways
NAF changes the job in three ways: OOC joins LGS as a primary metric; the VCD becomes mandatory; and the waste stream is classified oily waste. Plan the NAF solids programme as its own job — not a WBM job with different mud.