The tank system is where the whole removal train either gets a fair chance at the solids or doesn't. This is the deep reference: compartment order and routing, surface volume and sand traps, structural and valve failures, dead zones and settled beds, the pit-volume instrumentation that underpins kick detection, and the day-to-day routing failures that waste the equipment you already have.
Where it sits: the active tank system holds the mud between trips through the well and routes it through each removal stage in sequence before it returns to the suction. Its arrangement, volume and agitation decide whether the shakers, cyclones, centrifuge and degasser can actually do their jobs — and its pit-volume measurement is a front-line kick/loss indicator.
The tank system is the stage everyone ignores — but the order of compartments, the routing and the surface volume decide whether every removal unit even gets a fair chance at the solids.
Wrong compartment order (removal vs addition sequence)
Mechanism
Solids-removal equipment must process mud in the right order — shaker → degasser → desander → desilter → centrifuge — each drawing from and returning to the correct compartment, before chemicals/weight are added.
Shows as
Equipment re-processing treated mud or untreated mud bypassing a stage; removal effectiveness collapses.
Detect / inspect
Trace the actual flow path against the intended removal sequence; check suction/discharge compartments for each unit.
Consequence downstream
Solids that should have been removed reach the active and the suction; dilution rises.
Correction
Arrange compartments so mud flows through each removal stage in order, then to addition/suction; correct mis-routed suction/discharge lines.
Insufficient surface (active) volume / no buffer
Mechanism
Too little surface volume gives mud no residence time and no buffer, so removal equipment can't keep up and properties swing.
Shows as
Fast property swings, equipment overwhelmed at high rate, no settling time.
Detect / inspect
Compare active surface volume to circulation rate and the removal train's capacity.
Consequence downstream
Poor removal, unstable mud, more dilution.
Correction
Provide adequate surface/active volume for the rate; add buffer capacity; don't run the system starved.
Dead compartments / poor interconnection (short-circuiting)
Mechanism
Bad equalisation or routing lets mud short-circuit from inlet to suction, skipping treatment compartments.
Shows as
Untreated mud reaching the suction; treated mud sitting unused.
Detect / inspect
Dye/flow-trace the path; check equalisation gates and overflow arrangements.
Consequence downstream
Solids and gas reach the pumps; treatment wasted.
Correction
Fix equalisation and routing so mud must pass through treatment; eliminate short-circuit paths.
No sand trap / settling section after the shaker
Mechanism
A settling compartment (sand trap) right after the shaker catches solids that bypass screening; without it they go straight into the active.
Shows as
Sand accumulating in the active and at the suction.
Detect / inspect
Check for a sand trap downstream of the shaker; inspect for solids carry-through.
Consequence downstream
Solids load the hydrocyclones, centrifuge and pumps.
Correction
Provide and regularly clean a sand trap/settling section after the shaker.
Mechanical & structural failures
Tanks corrode, leak, and accumulate solids; their valves, gates and lines fail in the abrasive, weather-exposed environment.
Settled-solids beds in tank bottoms / dead zones
Mechanism
Where agitation doesn't reach, solids settle into beds that reduce active volume and barite sags out.
Shows as
Hard beds in tank corners/bottoms; lost volume; barite sag; weight variation.
Detect / inspect
Sound the tank bottoms; inspect dead zones; watch for weight stratification.
Consequence downstream
Lost volume, inconsistent mud weight, barite loss.
Correction
Improve agitation coverage (agitators/mud guns); clean out beds; eliminate dead zones (see agitators page).
Tank corrosion, cracking and leaks
Mechanism
Steel tanks corrode and crack at welds and the bottom; leaks lose mud and create hazards.
Shows as
Weeping/leaking welds and seams; lost mud; corroded plate.
Detect / inspect
Inspect welds, seams and the underside; check for wet spots and corrosion.
Consequence downstream
Mud loss, environmental and structural risk.
Correction
Repair welds, treat corrosion, coat where needed; inspect tanks on schedule.
Valve, gate and equalisation-line failures
Mechanism
Gate valves and equalisation lines seize, leak or block, breaking the intended routing.
Shows as
Stuck/leaking gates; lost control of compartment routing.
Detect / inspect
Operate valves/gates for free movement; inspect equalisation lines for blockage.
Consequence downstream
Mis-routing and short-circuiting.
Correction
Service/replace valves and gates; clear lines; keep routing controllable.
Mud gun / distribution line erosion and plugging
Mechanism
Mud guns and their lines erode at nozzles and plug with solids, losing the agitation/blending they provide.
Shows as
Weak or dead mud guns; local settling; uneven blending.
Detect / inspect
Check mud-gun flow and nozzles; inspect lines for erosion/plugging.
The tank system carries the pit-volume measurement that is central to kick detection, plus level and density instruments — failures here are well-control as well as process issues.
Pit-volume (PVT) sensor drift or failure
Mechanism
Pit-volume totaliser sensors are central to kick/loss detection. Fouling, coating or calibration drift makes them unreliable.
Shows as
Pit-volume readings disagreeing with reality; missed gains/losses.
Detect / inspect
Cross-check pit levels manually; verify calibration; inspect sensors for coating.
Consequence downstream
Missed kick/loss indication — a well-control risk.
Correction
Clean and calibrate PVT sensors on schedule; verify against manual checks; keep alarms live.
Level sensors / alarms fouled or mis-set
Mechanism
Tank level sensors foul in the coating mud and alarms drift or are disabled.
Shows as
Wrong levels, nuisance/missed alarms; overflow or run-dry risk.
Detect / inspect
Verify level readings vs physical; check alarm set points; inspect for coating.
Consequence downstream
Overflows, run-dry suction, lost early warning.
Correction
Maintain/calibrate level instruments; keep alarms enabled and correct.
Density / flow instrumentation unreliable
Mechanism
Inline density and flow instruments foul and drift, undermining mud-weight and balance control.
Shows as
Inaccurate weight/flow data; control decisions on bad numbers.
Detect / inspect
Cross-check against manual mud checks; calibrate.
Consequence downstream
Poor mud-weight control.
Correction
Calibrate/clean instruments; confirm against manual checks.
Operational & process failures
How the system is run day to day — routing, cleaning, transfers — decides whether the designed-in capability is actually realised.
Removal equipment lined up to the wrong compartments
Mechanism
Crews line up cyclones/centrifuge suction and return to convenient rather than correct compartments, so units re-process or bypass.
Shows as
Units running but solids still rising; treated mud re-processed.
Detect / inspect
Audit each unit's actual suction/discharge against the intended sequence.
Consequence downstream
Wasted removal capacity; LGS up.
Correction
Line every unit up to the correct compartments in sequence; lock and label the routing.
Tanks not cleaned / solids accumulation tolerated
Mechanism
Settled beds are left to build, shrinking active volume and sagging barite.
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 and mud-system practice and field references (drilling-fluid handbooks; rig surface-system arrangement 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.
Is your tank system helping the equipment — or fighting it?
Wrong routing, dead zones and short-circuits quietly waste every removal unit on the rig and force dilution. An independent evaluation audits the compartment sequence, the volumes and the agitation as one system.
