The desilter is the fine hydrocyclone stage — banks of small cones making the finest hydrocyclone cut before the centrifuge. This is the deep reference: cone sizing and feed system, the discharge-read process failures (roping, plugging, feed head), and the fast mechanical wear of small cones, apexes and vortex finders.
Where it sits: after the desander on unweighted mud, ahead of the centrifuge. Its many small cones make a fine cut but plug and wear faster than larger cones, and like the desander it strips barite if run bare on weighted mud — where it should instead be a mud cleaner.
A desilter is a bank of small hydrocyclones making a finer cut than the desander — the last hydrocyclone stage before the centrifuge. Its faults are about cone size/number, feed head and duty.
Too few / too-large cones for the fine cut
Mechanism
Desilter cones (typically 2–4 in) make a fine cut (~15–44 micron). Fewer or larger cones than needed shift the cut coarse and overload the bank.
Shows as
Fine silt passing through to the centrifuge and active; high LGS.
Detect / inspect
Compare cone size/number and rated capacity to circulation rate and target cut; sample overflow.
Consequence downstream
Fine LGS loads the centrifuge and forces dilution.
Correction
Size the bank with enough small cones for the rate and fine cut; add cones where the silt load demands.
Run unprotected on weighted mud (barite to waste)
Mechanism
Like the desander, plain desilter cones discard solids finer than the desander cut — on weighted mud that strips barite.
Shows as
Barite in the underflow; expensive loss; dilution to rebuild weight.
Detect / inspect
Check whether the bare desilter runs on weighted mud; sample underflow for barite.
Consequence downstream
Costly barite loss.
Correction
On weighted mud, convert to a mud cleaner (cones over a fine screen) so barite is recovered; don't run a bare desilter on weighted mud.
No dedicated feed pump / wrong head
Mechanism
Small cones need adequate feed head from a dedicated pump; sharing or undersizing starves them.
Shows as
Weak spray, poor fine cut; carry-over.
Detect / inspect
Check for a dedicated, sized feed pump; measure feed pressure vs head target.
Consequence downstream
Poor fine removal; centrifuge overloaded.
Correction
Provide a dedicated, correctly sized feed pump for the desilter bank.
Wrong order in the train (ahead of the desander)
Mechanism
Desilters should follow desanders on unweighted mud; running them first overloads the small cones with sand.
This reference describes failure modes and engineering principles in general terms. Corrective actions must be matched to your actual equipment, fluid, formation and procedures, and carried out under the relevant rig and safety standards.
Grounded in standard solids-control practice and field references (drilling-fluid solids-control handbooks; hydrocyclone operating practice). SC DrillTech is independent and vendor-neutral.
Take it further
Tools and references built from the same field experience as this page — independent and vendor-neutral.
Are your desilters removing silt — or passing it to the centrifuge?
Fine cones that rope, plug or wear quietly send fine LGS to the centrifuge and into dilution. An independent evaluation reads every cone, checks the feed head, and balances the bank to the cut it should be making.
