The PSD Knowledge Center
PSD describes the size distribution of the sampled solids. Read it with solids concentration, material identity, stream flow and operating conditions before assigning a separation duty.
1What is PSD?
PSD reports a distribution on a stated number, mass or volume basis and within the method’s measurement range. Equipment separation bands overlap and vary with particle density, shape, fluid rheology and throughput; they are not fixed ownership boundaries.
2D10, D50, D90, D100 explained
PSD is read at percentile points — the size below which a given fraction of the solids lies:
| Value | Means | Tells you |
|---|---|---|
| D10 | 10% finer | The 10th percentile; size alone does not establish clay activity or material identity. |
| D50 | 50% finer (median) | The middle of the distribution — the single most-quoted size. |
| D90 | 90% finer | The 90th percentile; compare measured equipment separation, not a fixed stage boundary. |
| D100 | 100% finer | Sample D100 is a method-dependent upper percentile; API screen D100 is a separate laboratory separation test, not this sample percentile. |
Distribution width helps describe a sample, but does not by itself establish separation sharpness or the number of stages required. Test the actual fluid and separation duty.
3PSD vs the retort
Retort estimates oil, water and solids volumes with the required method corrections. Mud density and assumed component densities can estimate weighting material and low-gravity solids; salts, additives and density assumptions affect the result. PSD supplies size information, not solids identity. The retort test
A D50 of 20 µm is a sample median, not proof that a shaker removes none of the solids or that only a centrifuge can treat them. Check the complete PSD, concentrations, screen designation, stream balances and fluid properties before selecting a response.
4PSD vs dilution
A growing fine fraction can accompany increasing treatment and dilution demand, but PSD alone does not quantify that demand. Assess solids concentration, rheology, material identity, separation performance and the fluid/waste balance; no separator removes all colloidal material. High-dilution troubleshooting
Remove drilled solids early where practicable. Attrition and dispersion may increase the fine fraction, but clay activity is not determined by size alone. Evaluate mechanical treatment, fluid chemistry and dilution together.
5PSD vs centrifuge performance
A centrifuge preferentially separates particles according to settling behaviour. Its solids discharge and liquid discharge can have different PSDs, and the active-system response depends on which streams return. An effective separator need not shift the active mud coarser; an unchanged normalised PSD does not prove zero removal. Centrifuge recovery troubleshooting
Feed and liquid-effluent PSDs alone do not establish a device D50. Obtain representative feed and both discharge samples, stream rates and solids concentrations, close the solids balance, then calculate recovery by size class on one basis. Device D50 is the size at 50% recovery on that stated partition-curve basis. Decanter centrifuge guide
6Fine solids & LGS
LGS is a density/material category, not a particle-size fraction. It can include coarse and fine drilled solids and low-density additives. Barite may also occur in fine size classes. PSD alone cannot identify LGS, reactive clay or MBT response. Low-gravity solids and dilution The retort test
Trend comparable samples using the same preparation, instrument and reporting basis. Interpret changes with retort, density, rheology, MBT where applicable and solids mass balance; PSD is not a guaranteed leading indicator.
7PSD interpretation guide
Reading a PSD in the field comes down to a few questions:
- Where is D50? A falling median prompts checks of sample basis, material mix and solids concentration; it does not alone prove removal failure.
- Is the fraction below a fixed fine-size threshold increasing? Compare a fixed size threshold on the same reporting basis. D10 itself moves with the distribution and always denotes the 10th percentile.
- Is the coarse end (D90+) where it should be? Coarse particles prompt checks of sampling, screen designation and possible shaker bypass; the PSD alone does not establish the cause.
- Did the curve shift after the centrifuge? Compare concentrations and solids flow in feed and both discharges. An unchanged normalised PSD can coexist with solids removal.
Use size trends as investigation prompts rather than equipment diagnoses. Compare measured duty, bypass, throughput, material identity and the actual return/discard routing across the train. Hydrocyclone guide Decanter centrifuge guide
8PSD case studies
Illustrative scenario: D50 falls from 45 to 22 µm while dilution rises and a centrifuge runs six hours daily. Check sampling, solids concentration, actual fines-removal capacity, routing and rheology before attributing the change to hours. A longer run is justified only by a verified capacity balance and acceptable fluid losses. Centrifuge capacity and run hours
Illustrative scenario: coarse particles and abrasion prompt a check of screen integrity, bypass and sampling location. A coarse PSD tail alone does not prove a holed screen or establish its device cut point. Shaker screen-failure guide
Cases are illustrative of the method, not specific wells.
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Want your PSD read against the train?
Send representative PSD and retort results, sampling locations, stream rates and operating conditions for a scoped remote evaluation; findings depend on data quality and the agreed method.
