During drilling, the drill bit breaks rock into small fragments called drill cuttings. These particles travel upward through the well with the drilling fluid and eventually reach surface equipment. A shale shaker removes larger cuttings, while hydrocyclone-based equipment such as desanders and desilters separates smaller particles that remain in the fluid.

The two machines perform similar functions but are designed for different particle sizes. A desander generally targets coarser sand-sized solids, while a desilter handles finer silt-sized particles. OSHA describes a desander as a centrifugal device for removing sand from drilling fluid and a desilter as a similar device used for very fine particles or silt.

Why Solids Control Is Needed

Drilling fluid, commonly called drilling mud, performs several important functions inside a well. It helps cool and lubricate the drill bit, carries rock fragments toward the surface, helps control formation pressure, and supports the open wellbore.

As drilling continues, solid particles continuously enter the circulating fluid. If too many unwanted solids remain in the mud, they can change its physical properties and increase abrasive loading on pumps and other equipment.

The solids-control system therefore separates particles at different stages so that the drilling fluid can continue circulating with appropriate properties.

Basic Drilling-Fluid Circulation

A simplified drilling-fluid path can be described as:

Well → Return line → Shale shaker → Desander → Desilter → Mud tank → Mud pump → Well

Actual configurations can differ according to the drilling method, mud type, equipment arrangement, and operating requirements.

OSHA's drilling-fluid circulation diagram shows drilling mud returning from the well to the shale shaker, followed by equipment including the desander, desilter, and degasser before the mud returns to the tank and is pumped back into the well.

Main Components

A typical hydrocyclone solids-control arrangement can include several components.

• Feed pump: Moves drilling fluid into the hydrocyclone under pressure.

• Hydrocyclone cones: Create the centrifugal separation effect.

• Feed manifold: Distributes drilling fluid to multiple cones.

• Overflow outlet: Allows the lighter fluid fraction to leave the upper part of the cyclone.

• Underflow outlet: Releases concentrated solids and a portion of the liquid.

• Support structure: Holds the cones, manifolds, piping, and related equipment.

• Valves and pressure gauges: Help control and monitor operating conditions.

Importance

Removing Abrasive Solids

Drilled solids can contain hard and abrasive mineral particles. Keeping these particles under control can help reduce unwanted wear within pumps and other circulating equipment.

This is one reason desanders are positioned within the solids-control sequence. OSHA specifically notes that desanders remove sand from drilling fluid to help prevent pump abrasion.

Maintaining Drilling-Fluid Properties

Drilling fluid is formulated with particular physical and chemical characteristics for a specific drilling environment. Excessive unwanted solids can influence properties such as density, viscosity, and flow behavior.

Desanders and desilters help remove selected portions of these solids so that the mud system can be monitored and adjusted according to drilling requirements.

Supporting Downstream Equipment

Solids-control equipment normally works as a sequence rather than as isolated machines. Larger particles are removed earlier, while progressively finer particles can be handled by later equipment.

A desander can therefore reduce the solid load reaching a desilter. The desilter then handles finer material that remains after earlier separation.

Improving Mud Circulation

A controlled solids concentration can help maintain predictable drilling-fluid behavior. This is important because the mud must travel through pumps, drill pipe, the annular space around the drill string, and surface equipment.

Maintaining appropriate fluid properties is also connected with well-control considerations. OSHA notes that drilling-fluid pressure helps counter formation pressure and that maintaining the mud system is part of well-control activity.

Desander vs. Desilter

Particle ranges are not universal because separation depends on cone design, pressure, fluid properties, solids characteristics, and operating conditions. The figures often quoted for desanders and desilters should therefore be treated as typical ranges rather than fixed limits.

Recent Updates

Updated Drilling-Fluid Processing Guidance

A significant recent development is the sixth edition of API RP 13C, published in December 2023. The recommended practice covers procedures for assessing and modifying the performance of solids-control equipment systems used in petroleum and natural-gas drilling-fluid processing.

In 2026, an erratum was issued for API RP 13C:2023. Current standards information identifies the amended version as API RP 13C:2023/ERR 1:2026.

This is relevant because solids-control performance is increasingly evaluated as a complete processing system rather than by looking at one piece of equipment in isolation.

More Focus on System Performance

Modern drilling operations can involve high circulation rates, complex well profiles, different drilling-fluid formulations, and changing formation conditions. These factors increase the importance of evaluating how the entire solids-control sequence behaves.

API RP 13C specifically addresses evaluation of solids-control systems rather than simply comparing individual machines.

Improved Hydrocyclone Design

Hydrocyclone technology continues to develop through changes in cone geometry, materials, manifold arrangements, pressure management, and equipment layout.

A hydrocyclone has no conventional rotating mechanical assembly. Instead, drilling fluid enters the cone tangentially, creating a strong swirling motion. Centrifugal effects move denser solids toward the outer wall and downward, while a cleaner fluid stream moves upward through the central vortex.

Monitoring and Data Collection

Modern drilling systems increasingly collect information about mud density, flow rate, pressure, solids concentration, equipment condition, and other operating variables.

Combining this information with automated controls can help drilling teams identify changes in solids loading and operating conditions. However, automated monitoring still requires appropriate calibration, inspection, and human interpretation.

Integration With Other Solids-Control Equipment

Desanders and desilters are increasingly considered as components of broader solids-control systems that can include shale shakers, mud cleaners, centrifuges, degassers, pumps, tanks, and automated monitoring systems.

The appropriate configuration depends on the drilling-fluid system and operating conditions. A single equipment arrangement cannot be applied universally to every well.

Laws or Policies

International Standards

There is no single worldwide law that governs every desander and desilter installation. Drilling operations are subject to the laws, regulations, technical standards, environmental requirements, and workplace rules applicable in the country or offshore jurisdiction where the operation takes place.

For petroleum drilling-fluid processing, API publications are widely used as technical references. API RP 13C provides procedures for evaluating drilling-fluid processing systems and solids-control equipment.

Workplace Safety

Drilling-fluid systems contain pumps, pressurized piping, rotating equipment, tanks, chemicals, electrical systems, and other hazards.

For example, OSHA identifies hazards around mud circulation systems including being struck by equipment, slips and falls, fluid exposure, and drowning hazards around mud tanks. Its guidance also points to measures such as lockout/tagout, appropriate personal protective equipment, guards, and guardrails.

Other countries have their own occupational-safety authorities and requirements.

Environmental Requirements

Drilling fluids and separated solids must be managed according to the environmental rules applicable to the drilling location.

Requirements can address waste handling, fluid containment, discharge, transportation, storage, and disposal. Offshore operations can also be subject to additional marine and environmental requirements.

Equipment Inspection

Desanders and desilters operate with pressurized drilling fluid. Their cones, manifolds, valves, hoses, pumps, tanks, and connections therefore require inspection according to the applicable equipment specifications and operating procedures.

Inspection frequency and procedures depend on equipment design, manufacturer instructions, drilling conditions, and local regulatory requirements.

Well-Control Requirements

Solids control is connected with the broader drilling-fluid system, but desanders and desilters themselves are not well-control devices.

Well control depends on maintaining appropriate drilling-fluid pressure, monitoring the mud system, using appropriate barriers, and applying established procedures. OSHA identifies drilling-fluid pressure monitoring and blowout preventers as components of well-control activity.

Tools and Resources

Hydrocyclone Pressure Gauges

Pressure measurements at the hydrocyclone feed can help operators understand whether the equipment is receiving the intended operating conditions.

Changes in pressure can influence separation performance, so pressure monitoring is an important part of operating a hydrocyclone system.

Mud Testing Equipment

Drilling-fluid testing equipment can measure properties such as density, viscosity, filtration characteristics, and other parameters.

API maintains recommended practices covering field and laboratory testing of drilling fluids, including API RP 13B-1, API RP 13B-2, and API RP 13I.

Particle-Size Analysis

Particle-size analysis helps identify the distribution of solids within drilling fluid. This information can be useful when evaluating whether a desander or desilter is removing the intended fraction.

The particle size of removed solids is also part of the evaluation procedures described within API RP 13C.

Mud-Tank Monitoring

Mud tanks are central parts of many circulating systems. Monitoring tank levels, flow conditions, density, and fluid characteristics can help operators identify changes within the mud system.

Solids-Control Performance Evaluation

API RP 13C provides a structured approach for evaluating drilling-fluid processing systems. Such evaluation can examine how the different pieces of equipment work together rather than looking only at one cone or machine.

Manufacturer Documentation

Equipment manuals contain important information about operating pressure, flow requirements, cone configuration, maintenance procedures, inspection points, and replacement components.

These documents should be used alongside applicable regulations, technical standards, and site-specific operating procedures.

FAQs

What are desanders and desilters in drilling?

Desanders and desilters are hydrocyclone-based solids-control equipment used to remove unwanted solid particles from drilling fluid. Desanders generally handle coarser particles, while desilters target finer solids.

How does a desander work?

A desander sends drilling fluid into a hydrocyclone under pressure. The fluid begins to rotate, causing denser solid particles to move toward the cone wall and downward toward the underflow outlet while the cleaner fluid moves upward.

What is the difference between a desander and a desilter?

The primary difference is the particle size each device is designed to separate. Desanders generally use larger hydrocyclones for coarser solids, while desilters use smaller cones to separate finer particles.

Where are desanders and desilters installed?

They are normally integrated into the surface drilling-fluid circulation system. A common arrangement places them after the shale shaker, with the desander ahead of the desilter, although actual layouts can vary by drilling operation.

Why are desanders and desilters important in drilling?

They help control unwanted sand and silt-sized solids in drilling fluid. This can support appropriate mud properties, reduce abrasive loading, and help downstream solids-control equipment operate within its intended role.

Conclusion

Desanders and desilters are important components of drilling-fluid solids-control systems. Both use hydrocyclone principles, but they are designed to handle different portions of the solid-particle distribution, with desanders generally targeting coarser material and desilters handling finer particles. Recent developments include updated API RP 13C guidance, improved hydrocyclone designs, greater system-level evaluation, and increased use of monitoring technologies. Their operation must be considered together with drilling-fluid management, workplace safety, environmental requirements, and the regulations applicable to each drilling location.