Poor hole cleaning doesn't just risk a pack-off — it dumps a surge of solids on the shakers the moment you circulate bottoms-up. Annular velocity is the first check: is the mud moving fast enough to carry cuttings out faster than they fall back?
Why solids control cares about hole cleaning
Cuttings that aren't transported out settle, accumulate and then arrive at surface all at once as a slug — overloading screens, spiking the centrifuge feed and driving dilution. Hole cleaning and solids control are the same problem seen at two ends of the well: what the annulus fails to carry, the shakers pay for later.
Velocity versus slip
Annular velocity is how fast the mud travels up the annulus. Against it works the cutting's slip velocity — the speed it falls back through the mud (the Stokes idea, scaled up). Net transport is the difference. Express it as a transport ratio: the fraction of annular velocity that actually moves cuttings upward.
The equation
Annular velocity from flow rate and geometry:
AV (ft/min) = 24.5 × Q ÷ (Dh² − Dp²)
Cuttings transport ratio:
Transport ratio = (AV − Vslip) ÷ AV
Q = flow rate in gpm; Dh, Dp = hole and pipe OD in inches; Vslip = cutting slip velocity (ft/min).
A transport ratio comfortably above ~0.5 is good in vertical wells; in high-angle sections cuttings beds form even at higher velocities, so treat annular velocity as necessary but not sufficient, and watch the shaker for the slug that says the hole finally cleaned up.
Common questions
What annular velocity is enough?
There's no single number — it depends on hole angle, mud rheology and cutting size. Judge it by the transport ratio and by what arrives at the shaker, not by velocity alone; deviated wells need more than the vertical rule of thumb.
How does hole cleaning show up at the shakers?
As timing and load. A poorly cleaned hole holds cuttings back, then releases them as a heavy slug on bottoms-up that floods the screens and spikes the centrifuge feed — a solids-control problem that started thousands of feet down.
