drilling · hydraulics
Cuttings Transport Ratio
click formula to derive ↑
Inputs
ft/s
ft/s
Description
Computes the cuttings transport ratio — the fraction of annular velocity that goes toward actually carrying cuttings out of the hole, after subtracting how fast those cuttings fall back through the fluid — from Annular Velocity and cuttings Slip Velocity. This is the combined hole-cleaning check that both of those calculators feed into; "Cuttings Transport" and "Hole Cleaning" are the same underlying question under two backlog names, closed here as one calculator rather than two near-duplicates.
Variables
| Symbol | Unit | Description |
|---|---|---|
| CTR | % | Cuttings Transport Ratio |
| Vnet | ft/s | Net Cuttings Rise Velocity |
| Va | ft/s | Annular velocity of the drilling fluid, from Annular Velocity. |
| Vs | ft/s | Cuttings slip (settling) velocity, from Slip Velocity. |
Assumptions
- Annular Velocity and Slip Velocity are evaluated at the same point in the wellbore, using consistent mud and cuttings properties
- A vertical or near-vertical well — in deviated or horizontal sections, cuttings beds form on the low side of the hole through a different mechanism (cuttings bed erosion/rolling transport) that this simple ratio does not model
- A single representative cuttings size and density, the same simplification already made by Slip Velocity
Limitations
- The commonly used 50% minimum threshold is a field rule of thumb, not a precisely derived universal value — actual required transport ratio varies with hole size, cuttings concentration, and rig-specific hole-cleaning history
- Does not model deviated or horizontal wellbore hole cleaning, where cuttings-bed formation and mechanical erosion (not simple slip-velocity subtraction) govern transport — a materially different physical problem
- Inherits both Annular Velocity's and Slip Velocity's own single-representative-value simplifications; does not account for a real cuttings size/density distribution or annular velocity profile
Use Cases
- → Real-time hole cleaning monitoring: Check whether current flow rate and mud properties provide adequate cuttings transport before continuing to drill ahead.
- → Hydraulics program design: Determine the minimum flow rate or mud rheology adjustment needed to bring transport ratio above the target threshold for a planned hole section.
- → Pack-off / stuck-pipe risk screening: Flag intervals where a low or negative transport ratio indicates cuttings accumulation risk before it develops into a pack-off or stuck-pipe event.
Related Calculations
Region Notes
Global
Large-diameter surface hole sections with high annular capacity often struggle to reach adequate annular velocity at normal flow rates — transport ratio should be checked explicitly in large-hole sections rather than assumed adequate from experience in smaller intermediate/production sections.
References
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