On a non-aqueous well, retention-on-cuttings above the limit (EPA 40 CFR 435: 6.9% NAF) turns recoverable fluid into reportable waste and haul-off cost. Every point of OOC left on the cuttings is base oil bought and thrown away.
Likely causes
Screen basket too coarse, worn or holed — fluid not spun off.
Worn rotor tips / wide screen gap — cake not scraped and re-exposed.
Low effective G / bowl speed — belt slip, motor or VFD fault.
Feed rate too high — the bed is too thick for the residence time.
Effluent line backing up — floods the bowl and re-wets the cake.
Feed too cold or too viscous — base oil won't release in time.
Solids loading beyond the dryer's drying capacity.
How to diagnose it
Retort the discard for oil / water / solids %.
Read the cake — free-flowing dry granules vs a wet smear.
Confirm bowl speed / G and check for belt slip.
Inspect the basket for wear, holes or near-size blinding.
Check rotor-tip / screen clearance and the effluent line.
The fix — step by step
Set the feed to a steady, rated rate — surging and over-feeding are the usual cause.
Restore full G: fix belt slip, confirm VFD speed, clear mechanical drag.
Replace a worn or holed basket; match aperture to the cuttings size.
Reset rotor tips / clearance so the cake is scraped and re-dried.
Clear the effluent line so recovered fluid leaves and the bowl doesn't flood.
Confirm it's fixed
✓ Verify: Retort confirms OOC under target and the discharge limit; discard leaving as dry, free-flowing granules.
Field note. The dryer is the single biggest recovery on an oil-based well — every point of OOC you leave is base oil you bought and then pay again to haul away. Measure it with a retort, not the eye: ‘looks dry' has signed off a lot of barrels that weren't.
The 10 Solids-Control Numbers Every Engineer Must Track — what to measure, the formula, the field target and the red flag. Grounded in API RP 13B-1, RP 13C, EPA 40 CFR 435 & OSPAR.