Capillary Number Calculator
Enter the required velocity, viscosity, and interfacial-tension inputs. The calculator returns dimensionless capillary number.
Calculation context and source notes
Capillary number compares viscous forces with capillary forces and is commonly used as a rock-fluid screening parameter in displacement and recovery calculations.
Use it for reservoir engineering and enhanced-oil-recovery screening when velocity, viscosity, and interfacial tension are known.
Solves for
N_c (dimensionless)
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Formula, variables, and sourceRelated source-backed guides
Formula, variables, and default calculation
Reproducible default result
With the default values shown below, the calculation returns N_c = 0.000001 dimensionless. Defaults demonstrate the implementation; they are not recommended field values.
1
10
30
Input definitions
mu_w
cPViscosity of Displacing Fluid
V
ft/dayCharacteristic Velocity
sigma_ow
dyn/cmInterfacial Tension between Oil and Water
Output definitions
N_c
Capillary Number
mu_w
Viscosity of Displacing Fluid (rearranged)
V
Characteristic Velocity (rearranged)
sigma_ow
Interfacial Tension (rearranged)
Engineering use, assumptions, and limits
Use it for reservoir engineering and enhanced-oil-recovery screening when velocity, viscosity, and interfacial tension are known.
Assumptions
- Velocity, viscosity, and interfacial tension are representative of the displacement being evaluated.
- The selected equation form matches the units declared by the formula record.
- The result is interpreted as a screening ratio, not a complete displacement model.
Limitations
- Does not include relative permeability, wettability alteration, pore-scale heterogeneity, or phase trapping directly.
- Cannot by itself predict recovery factor or residual oil saturation.
Common mistakes
- Mixing viscosity and interfacial tension unit systems.
- Treating a dimensionless ratio as a standalone EOR design result.
- Comparing capillary numbers without confirming the same definition was used.
Frequently asked questions
What inputs does the Capillary Number calculator need?
The calculation uses Viscosity of Displacing Fluid (mu_w), Characteristic Velocity (V), Interfacial Tension between Oil and Water (sigma_ow). Enter values on the units shown beside each field.
What result does this calculator return?
The primary result is capillary number in dimensionless. The formula section shows the declared relationship, variables, and a reproducible default calculation.
What should I check before using the result?
Confirm the unit basis, source applicability, and input quality. Does not include relative permeability, wettability alteration, pore-scale heterogeneity, or phase trapping directly. Mixing viscosity and interfacial tension unit systems.
Source and record status
Source metadata identifies the relationship implemented by the calculator. Check the cited edition, unit basis, and scope against the engineering case before operational use.
Lake, L. W. (1989). Enhanced Oil Recovery. Prentice Hall, Chapter 4.
Open source reference