On an unweighted water-based mud, running a bank of desilters is straightforward — the cones cut silt-sized drilled solids and discard them, and the only solids in the underflow are the ones you wanted to remove. On a weighted mud, the same bank becomes a liability: barite is ground to pass 200 mesh (roughly 74 microns and finer), which puts it squarely in the desilter's cut range. Run bare desilters on weighted mud and you discard weight material you paid for, then immediately have to add more to rebuild the density. The mud cleaner exists to solve exactly this problem.
What a mud cleaner is
A mud cleaner is not a separate piece of equipment — it is a desilter bank with an underflow screen added beneath the cone discharge. The cones process the full circulating rate at normal feed head and make their usual silt-sized cut. Instead of falling to a discard pit, the combined underflow — barite and drilled silt together — drops onto a fine vibrating screen, typically in the 150–200 mesh range (74–100 microns). That screen makes the final separation:
- Barite (finely ground, passing 74 µm) passes through the screen and drops back into the active system — recovered.
- Drilled silt (coarser than the screen cut, or agglomerated) is retained on the screen and discharged as waste.
When to use it — and when not to
| Mud type | Use bare desilters? | Use mud cleaner? |
|---|---|---|
| Unweighted WBM (no barite) | Yes — the underflow is all drilled solids | Not needed |
| Weighted WBM or OBM with barite | No — you will discard barite | Yes — protects the weight material |
| Lightly weighted, barite modest | Marginal — depends on mud cost vs removal need | Preferred when solids removal is needed |
The crossover point is usually around the mud weight where the barite you would lose through bare desilters costs more than the mud cleaner's operating inconvenience. In practice, most weighted programmes switch to a mud cleaner well before that — because losing barite also means adding make-up barite to hold weight, compounding the cost.
Screen selection for the underflow
The screen beneath the cones has to be fine enough to pass barite but coarse enough to retain the drilled silt you are trying to remove. The standard range is 150–200 mesh (roughly 74–100 µm cut per API RP 13C), but the right choice depends on the barite grind and the silt distribution in the active mud:
- Too fine a screen — barite starts to be retained with the silt; you lose weight material and the screen loads up quickly.
- Too coarse a screen — drilled silt passes with the barite; the cleaner removes less than it should.
Watch the underflow discard under a hand lens: if you see bright, heavy particles (barite) in the discard, the screen is too coarse or the cones are not making a clean cut. If the barite recovery is good but LGS is still climbing, the screen may be too fine and holding drilled silt back into the active system.
Feed head still rules
The mud cleaner's performance lives or dies on the same variable as any cyclone — feed head. The desilter cones need roughly 75 ft of head to make their cut; below that, the separation degrades regardless of the screen beneath them. Check manifold pressure every tour, calculate head (h = 19.2 × p ÷ ρ), and treat a falling head as a worn feed-pump impeller until proven otherwise.
Key takeaways
The mud cleaner is the answer to the weighted-mud desilter problem: it lets you make the fine solids cut you need without throwing away the barite you are paying to keep. The cones separate by density and size; the underflow screen finishes the job by size alone, returning barite to the active system. Use bare desilters only on unweighted mud — on any programme with barite, the mud cleaner is not optional, it is the only way to run fine cyclone separation without eroding your own mud weight.
