The single fact that reshapes a solids-control plan is not the formation — it is what the mud is made of. Water-based mud is cheap, so you remove solids aggressively and accept some fluid loss. Oil- and synthetic-based muds are expensive invert emulsions, so the strategy inverts too: protect the base fluid at almost any cost. Same equipment on the rig, very different way of running it.
Unweighted water-based mud: run the full train
On unweighted WBM the fluid is inexpensive and its solids tolerance is higher, so the job is simply to take out as much drilled solid as the train can catch. That means the full cascade run hard: shale shakers on the finest screen that conveys, then desanders, then desilters, then a decanter centrifuge for the fines. There is no barite to protect and the liquid phase is cheap, so the hydrocyclones can cut aggressively and the small fluid losses in their underflow do not matter much.
The enemy here is the fine, low-gravity silt that drives up plastic viscosity and gel strengths and abrades pumps, so the emphasis falls on the desilters and the centrifuge — and sometimes on flocculants added upstream to ‘grow’ the fines into a size the cones can catch. This is the one fluid type where the textbook order and the aggressive settings apply without caveat. Confirming that the removal efficiency is actually where it should be, tour over tour, is what Rig IQ is for.
Weighted mud: protect the barite
The moment the mud is weighted with barite, one stage becomes a liability. Because a hydrocyclone sorts by mass, a desilter on weighted mud sends dense barite (specific gravity 4.2) out the apex along with the drilled solids — so a bare desilter is now throwing away expensive weighting material. The fix is to bypass the bare desilter and recover the barite instead: a mud cleaner (desilter cones over a fine screen) returns the fine barite to the system, or a barite-recovery centrifuge does the same job on the finest fraction.
So on weighted mud the plan splits: shakers and a mud cleaner or barite centrifuge handle the balance between removing drilled solids and keeping barite, while a second high-speed centrifuge takes the ultrafines that would otherwise build up. This applies whether the base is water or oil — weighting changes the strategy independently of the base fluid. Working out whether the barite you would recover justifies the mud cleaner at your mud weight is a quick calculation in Rig IQ.
Oil- and synthetic-based mud: drop the cyclones, save the fluid
Non-aqueous fluids — OBM and SBM, both usually invert emulsions with the oil or synthetic as the external phase — change the economics completely, because the base fluid is expensive and every barrel lost is a barrel bought. Here the hydrocyclones become a problem: desanders and desilters discard a significant amount of the costly liquid phase in their underflow, so they are generally not cost-effective on NADF. The strategy shifts to fine shaker screens plus a high-performance decanter centrifuge to pull ultrafine and colloidal solids while keeping the fluid, and a vertical cuttings dryer to strip base fluid off the cuttings before disposal.
SBM behaves like OBM in the plant — same invert-emulsion handling, same base-fluid-recovery priority — with the added advantage that synthetic base fluids biodegrade more readily, which matters for offshore discharge limits. Either way the whole train is tuned around recovery, not aggression: the cuttings leave at 10–15% oil off the shakers and a dryer takes them below 5%, and the recovered fluid is rehabilitated on the centrifuge before it goes home. Modelling that base-fluid recovery and its cost against your fluid price is exactly the kind of decision Rig IQ is built to run.
Strategy by fluid type
Unweighted WBM (cheap): full aggressive train — shaker → desander → desilter → centrifuge. Cut hard; small fluid loss is fine.
Weighted mud (any base): bypass bare desilter → mud cleaner or barite-recovery centrifuge (save barite, SG 4.2) + high-speed centrifuge for fines.
OBM / SBM (expensive NADF): drop desanders/desilters (they dump base fluid) → fine screens + high-performance centrifuge + cuttings dryer. Recover the fluid; SBM biodegrades better.
Let the mud type set the strategy. Cheap unweighted WBM: run the full train hard and accept small fluid losses. Weighted mud: bypass the bare desilter and recover barite (mud cleaner or barite centrifuge), whatever the base. Expensive OBM/SBM: drop the cyclones (they dump base fluid), lean on fine screens, a high-performance centrifuge and a cuttings dryer, and tune everything around recovering the fluid.
Common questions
How does solids control differ between OBM and WBM?
On cheap water-based mud you run the full hydrocyclone-and-centrifuge train aggressively, because losing a little fluid to remove solids is worth it. On expensive oil-based mud the desanders and desilters discard too much costly base fluid, so they are generally dropped in favour of fine shaker screens, a high-performance centrifuge, and a cuttings dryer to recover the fluid.
Do you run desilters on oil-based mud?
Generally no. Desanders and desilters discard a significant amount of the expensive base fluid in their underflow, so they are not cost-effective on non-aqueous fluids. OBM and SBM instead rely on fine shaker screens and a high-speed decanter centrifuge to remove fine solids while keeping the base fluid.
Is solids control different for SBM versus OBM?
In the plant they are handled the same way — both are invert emulsions where the priority is recovering the expensive base fluid, so both use fine screens, a high-performance centrifuge and a cuttings dryer rather than hydrocyclones. The main difference is environmental: synthetic base fluids biodegrade more readily, which matters for offshore discharge.
