Porosity tells how much space a rock or filter has for fluid; permeability tells how easily fluid moves through it. Good oil reservoirs and aquifers need both.
How to use the Porosity and Permeability Calculator
- Flow rate Q
- Viscosity μ
- Sample length L
- Cross-section area A
- Pressure drop ΔP
- Mean residence time
Results update as you type, every field has its own unit menu, and everything is calculated in your browser.
How it works
Enter the measured flow, viscosity, sample length and area, the pressure drop and the mean residence time.
Inputs explained
| Field | What to enter |
|---|---|
| Flow rate Q | Units: mL/s, mL/min, m³/s |
| Viscosity μ | Units: mPa·s (cP), Pa·s |
| Sample length L | Units: cm, mm, m, in, ft |
| Cross-section area A | Units: cm², m² |
| Pressure drop ΔP | Units: kPa, Pa, bar, psi, atm, MPa |
| Mean residence time | Units: s, ms, min, h, days |
What each result means
- Permeability k = [Flow rate Q]×[Viscosity μ]×[Sample length L]÷([Cross-section area A]×[Pressure drop ΔP])÷9.869233e-13×1000
- In m² = [Flow rate Q]×[Viscosity μ]×[Sample length L]÷([Cross-section area A]×[Pressure drop ΔP])
- Porosity φ = [Flow rate Q]×[Mean residence time]÷([Cross-section area A]×[Sample length L])×100
Example values
How the main result changes when Flow rate Q changes and everything else stays at the example values above:
| Flow rate Q (mL/s) | Permeability k (mD) |
|---|---|
| 0.5 | 253.3125 |
| 0.75 | 379.9687 |
| 1 | 506.625 |
| 1.25 | 633.2812 |
| 1.5 | 759.9375 |
| 2 | 1,013.25 |
Formula
k = Q·μ·L/(A·ΔP), φ = V_pore/V_bulk = Q·t_res/(A·L)
Worked example
Inputs — Flow rate Q: 1 mL/s; Viscosity μ: 1 mPa·s (cP); Sample length L: 5 cm; Cross-section area A: 10 cm²; Pressure drop ΔP: 100 kPa; Mean residence time: 10 s.
Results — Permeability k = 506.62498 mD; In m² = 5.0000e-13 m²; Porosity φ = 20 %.
Key terms
- Porosity
- Fraction of volume that is pore space.
Frequently asked questions
Is high porosity always high permeability?
No – clay is porous but almost impermeable.
What is a millidarcy?
1/1000 darcy ≈ 9.87 × 10⁻¹⁶ m².
What porosity do sandstones have?
Typically 10–30%.
What is residence time?
Average time fluid spends in the sample.