desander, Oil & Gas Glossary

What Is a Desander?

A desander is a solids control device that removes coarse drilled solids — primarily sand-sized particles in the range of 45 to 75 microns — from drilling mud using hydrocyclone centrifugal separation, processing the overflow from the shale shaker screens to reduce the fine-solids loading that would otherwise accumulate in the recirculating mud system and degrade mud properties.

Key Takeaways

Desanders use hydrocyclones with cone diameters of 15-20 cm to develop centrifugal forces that separate particles denser than the fluid.
Cut point is typically 45-75 microns; particles above this size are discharged in the underflow; finer particles pass with the overflow back to the active system.
Desanders are positioned downstream of shale shakers and upstream of desilters in the solids control train.
Desanders process up to 500-1,500 LPM and are used only in unweighted or lightly weighted muds; barite in weighted mud would be removed with the solids.
Regular desander operation maintains low-gravity solid concentrations that protect pump liners, bit nozzles, and tool components from abrasive wear.

How Desanders Work

A desander uses one or more hydrocyclone units — conical devices with no moving parts in which centrifugal separation is driven by the tangential feed of mud under pressure. Mud is pumped tangentially into the top of the cylindrical upper section of the hydrocyclone, creating a rotating vortex. Centrifugal force drives denser particles (drilled sand and silt) toward the outer wall, where they spiral downward and exit through the apex underflow discharge. The cleaned mud, with finer particles and liquid, travels inward to form an inner upward-spiralling vortex that exits through the vortex finder at the top (overflow) and returns to the active mud pits.

The cut point of a hydrocyclone (the particle size at which 50% is removed versus 50% passes through) depends on the hydrocyclone diameter, feed pressure, and feed fluid properties. Larger diameter units (15-20 cm for desanders) produce coarser cut points because the centrifugal acceleration is lower for a given rotation speed in a larger-radius cone. Desanders are optimised for the 45-75 micron range corresponding to coarse silt and fine sand. The downstream desilter uses smaller cones (5-10 cm diameter) for a finer cut point of 15-30 microns. Together, desander and desilter remove the full range of drilled solids that cannot be captured by the shale shaker screens alone.

Desander Applications Across International Jurisdictions

In Canada, desanders are standard equipment on WCSB drilling rigs drilling surface and intermediate hole sections through soft Tertiary and Cretaceous formations where the rate of penetration is high and the volume of fine drilled solids generated per unit time can overwhelm shale shaker capacity alone. AER Directive 050 governs onshore drilling mud waste handling; desander underflow (wet cuttings and separated solids) requires management under the same regulations as shaker cuttings, typically road spreading on approved lease locations for unweighted water-based mud cuttings. Montney horizontal wells with high-volume slick water fracturing during completion sometimes use desanders on flowback fluid handling systems to protect pump equipment from produced formation sand.

In the United States, desanders are included in the standard solids control equipment specification for Gulf of Mexico drilling vessels and jackup rigs. EPA NPDES general permits for OCS drilling operations allow discharge of desander underflow solids from water-based mud systems meeting toxicity and physical criteria. In Norway, NORSOK D-010 and OSPAR zero-discharge requirements for OBM systems require containment of all desander underflow from oil-based mud drilling on NCS wells; desander underflow from OBM must be containerised and shipped to shore for treatment. In the Middle East, Saudi Aramco's drilling engineering standards specify desander equipment requirements for onshore and offshore wells; desander cut points and processing capacity are matched to the expected solids loading from the formation types being drilled.

Fast Facts

A single 15 cm (6-inch) diameter desander hydrocyclone processes approximately 500-750 litres per minute and removes particles above approximately 74 microns at typical drilling mud densities and viscosities. Desander units typically consist of 2-8 cones arranged in parallel manifolds to handle the total mud return flow rate from the well. The centrifugal force at the wall of a 15 cm cone operating at typical feed pressures is approximately 50-100 times gravitational acceleration, far exceeding the 1g settling force in a conventional open pit and enabling rapid separation of sand-sized particles that would settle only very slowly under gravity.

Desander Versus Desilter

Desanders and desilters are functionally identical hydrocyclone separators distinguished only by their cone diameter and resulting cut point. Desanders use larger cones (15-20 cm) to cut at 45-75 microns, removing coarse silt and fine sand. Desilters use smaller cones (5-10 cm) to cut at 15-30 microns, removing medium and fine silt. In a properly configured solids control system, desanders process the full mud return flow first, removing the coarser particles; the overflow then passes to the desilters for fine particle removal; the desilter overflow then passes to the mud-gas separator and centrifuges as needed. This cascaded arrangement ensures that the desilter cones are not immediately plugged by the coarser particles that the desander should have already removed.

Tip: Never run a desander on a weighted mud system (density above approximately 1.32 kg/L or 11 ppg) without a weighting agent return system on the underflow. At higher mud weights, the barite weighting agent has a particle size distribution that overlaps the desander cut point; running desander underflow to the waste pit discards expensive barite along with the undesirable drilled solids. This mistake can increase mud cost by hundreds of thousands of dollars on a long well and reduce mud density below the required level for well control. If desanding is required on a weighted mud, use a centrifuge with dilution instead, which separates fine drilled solids at a cut point well below barite particle size while returning barite to the active system.

Desander is also referenced as:

Sand hydrocyclone — the descriptive term used in equipment catalogues and solids control system specifications when referring to the specific hydrocyclone size and cut point of the desander
Coarse hydrocyclone — used in some solids control system design documents to distinguish larger-diameter desander cones from smaller desilter cones in the same system
Scalping unit — informal operational term used on some rigs when the desander is used specifically to scalp (remove) coarse solids from a specific high-solids mud stream before other processing

Frequently Asked Questions

Why should desanders not be used with weighted drilling mud?

Weighted mud uses barite (barium sulfate, density 4.2 g/cm³) as the primary weighting agent to increase mud density above the density achievable with drilled solids alone. Barite particles have a size distribution largely in the range 2-74 microns, which overlaps with the cut point of desander hydrocyclones. Running a desander on weighted mud causes barite to be discharged in the underflow along with the unwanted drilled solids, progressively depleting the barite from the mud system and requiring expensive barite additions to restore density. When fine-solid removal is needed in a weighted mud, centrifuges are used instead — they can be operated at lower G-force to selectively remove ultra-fine drilled solids at cut points below 5 microns while retaining the larger barite particles in the centrate returned to the active system.

How does mud viscosity affect desander performance?

Higher mud viscosity reduces the centrifugal separation efficiency of hydrocyclones because the viscous drag on particles in the rotating fluid increases, requiring larger centrifugal forces to move particles toward the outer wall at the same rate as in lower-viscosity mud. As yield-point-dominated muds with high gel strength enter the hydrocyclone, the yield point effectively inhibits particle settling, reducing separation efficiency and increasing the cut point above the design value. Desanders are most effective in low-viscosity, low-gel muds with yield points below approximately 20 lb/100 ft²; high-viscosity, high-gel muds should be diluted before desanding or processed at reduced flow rates to achieve the design separation efficiency.

Why Desanders Matter in Oil and Gas

Drilled solids accumulation in the active drilling mud system is one of the leading causes of preventable drilling problems, including high equivalent circulating density from excess solids loading, reduced ROP from re-grinding of fine solids under the bit, stuck pipe from filter cake thickening, and accelerated wear of pump liners, piston rods, and bit nozzles. Desanders are the second line of defence after shale shakers against fine-solid contamination, removing the particle size fraction that shaker screens with API 120-200 mesh cannot capture but that centrifuges would process slowly at excessive cost. The cost of a desander unit installation — a few thousand dollars per well — is recovered many times over in reduced pump liner wear, reduced chemical consumption to combat high-solids viscosity, and reduced bit runs required when clean mud is maintained throughout the drilling programme.