Primary solids control is the shale shaker — the first, cheapest, full-flow removal stage that takes the coarse cut straight off the flowline. Secondary solids control is everything finer that follows: the hydrocyclones (desanders and desilters), the mud cleaner, and the decanting centrifuge, each removing a smaller particle the stage before it left behind. The system is a cascade, sorted coarse to fine.
Primary: the shale shaker
The shaker handles 100% of the flow returning from the well and is the only stage that sees the whole stream. It is mechanical, simple and the cheapest barrel of removal on the rig — every solid it takes out is a solid the finer, costlier stages downstream never have to touch. A shaker running the right API screen sets the ceiling for the entire system: if it leaks coarse solids, everything below it is overloaded.
Secondary: finer cuts, in order
Secondary equipment cleans the fraction the shaker could not. Each stage makes a finer cut than the last:
| Stage | Equipment | Rough cut point | Role |
|---|---|---|---|
| Primary | Shale shaker | ~74–150 µm (screen-dependent) | Full-flow coarse removal |
| Secondary | Desander (hydrocyclone) | ~45–74 µm | Coarse sand the shaker passed |
| Secondary | Desilter / mud cleaner | ~15–44 µm | Fine silt; recovers barite on weighted mud |
| Secondary | Decanting centrifuge | ~2–7 µm | Finest cut; barite recovery / fines removal |
Why the order is fixed
Each stage protects the one after it. The shaker keeps coarse solids off the cyclone feed pump; the desander keeps the desilter cones from plugging; the desilter or mud cleaner reduces the load on the centrifuge. Run a stage out of order — or skip one — and you push a particle load onto equipment that was never sized for it. The cut points only line up if the stream passes through them coarse to fine.
The rule
Build the system from the top down. Get the shaker right first — the correct API screen, intact and properly tensioned — then let each secondary stage do the finer job it is built for. The centrifuge is the polish, not the rescue. If your fine-end equipment is always overloaded, the problem is usually upstream.
Key takeaways
Primary solids control is the shaker: full flow, coarse cut, cheapest removal. Secondary is the cyclones, mud cleaner and centrifuge, each making a finer cut in a fixed coarse-to-fine order. Every stage protects the next, and every barrel removed early saves money downstream. Fix the primary stage first; the secondary stages can only do their job if the shaker does its.