You can buy the best shakers, the sharpest cones and the biggest centrifuge on the market and still run a poor solids-control system — if they are plumbed in the wrong order. Solids control is a sequence, not a collection of machines. Each stage is designed to take the particle the stage before it could not, and getting the order — and the tank arrangement — right matters more than raw capacity.
The correct order, and why each step sits where it does
| # | Stage | Removes | Why here |
|---|---|---|---|
| 1 | Shale shakers | Coarse cuttings | First, so nothing downstream sees solids it wasn’t built for — and before any centrifugal pump. |
| 2 | Sand trap / settling | Fast-settling solids that bypass | A safety net under the shakers; never the primary tool. |
| 3 | Degasser | Entrained gas | Before the cyclone feed pump — gas-cut mud can’t be pumped or cut properly and destabilises the cone’s air core. |
| 4 | Desanders | Sand-sized solids | Coarse cyclone stage before the fine one, so desilters aren’t flooded with sand. |
| 5 | Desilters / mud cleaner | Silt-sized solids | Finer cyclone cut; the mud cleaner adds a fine screen to save barite on weighted mud. |
| 6 | Decanter centrifuge | Ultra-fine / barite duty | Last — the finest cut, and the only stage that can recover barite or strip colloidal fines. |
The principle: remove each solid once, at the first stage that can
A drilled solid that escapes the shaker doesn’t just cost you that stage — it gets ground finer with every trip around the system, until it is too small for any cone and only the centrifuge or dilution can touch it. The whole point of the sequence is to catch each particle at the coarsest stage capable of removing it, while it is still big and cheap to remove. Miss it early and you pay for it repeatedly, in a harder form.
The arrangement mistakes that quietly defeat good equipment
- Short-circuiting. Processed (clean) fluid leaking back into the dirty suction — usually a removed weir or an open equalising valve — so the same fluid is “cleaned” twice while new dirty fluid passes through unprocessed. The classic open gate valve.
- Processing in the wrong compartment. Each stage should draw from the compartment ahead of it and discharge to the one behind it; cross-plumbing blends clean and dirty and collapses efficiency.
- Running cyclones off the wrong pump. Feeding desilters from a pump sized for transfer, not for cone head — the cones never see their design feed head.
- Under-agitated compartments. Solids settle out of suspension and never reach the next stage — the centrifuge pit is the usual offender (see turnover/TOR).
Tanks are equipment too
The tanks are not just storage; their compartmentalisation is the sequence. Dirty (settling/suction) compartments feed the removal stages; clean (active) compartments hold processed fluid ready to pump downhole. Agitators and mud guns keep everything in suspension so it actually reaches the equipment instead of dropping out and being lost. A correctly arranged tank with modest equipment will out-clean a powerful spread that is cross-plumbed.
Key takeaways
Sequence beats horsepower. Coarse to fine, surface to centrifuge; degasser ahead of the cyclones; each stage on its own compartment with no short-circuit back to the suction. Get the order and the plumbing right and ordinary equipment performs; get it wrong and the best equipment on the market quietly under-delivers.