Hydrogen Cavern Cushion Gas Mass Calculator
Translate cavern volume, allowable pressure range, and temperature into the hydrogen cushion gas mass and deliverable working inventory.
Screening tool only; combine with geomechanical studies, cycling analysis, and HSE reviews before issuing design memoranda.
Examples
- 500,000 m³ cavern, 200 bar max, 60 bar min, 35 °C, Z = 1.05 ⇒ Cushion 2,248.18 t, working 5,245.76 t (ratio 2.33)
- 180,000 m³ cavern, 180 bar max, 70 bar min, 30 °C, default Z ⇒ Cushion 1,007.80 t, working 1,583.69 t (ratio 1.57)
FAQ
Why do I need cushion gas in a salt cavern?
Cushion gas keeps cavern pressure and brine displacement stable so the roof and walls remain supported. Without it, cycling to low pressures would reduce deliverability and risk salt sloughing or fresh water intrusion.
What temperature should I use?
Use the average bulk gas temperature expected during operation—typically close to the native rock temperature once equilibration occurs. Avoid inlet temperature because it swings during injection and withdrawal.
How do I obtain an appropriate compressibility factor?
Start with Z = 1.00 for scoping. For detailed design, use an equation of state such as GERG-2008 or a reservoir simulator tuned with laboratory PVT data across the planned pressure range.
Can the calculator handle brine compensation?
Yes, indirectly. The void volume input should reflect the free gas space after accounting for brine and any insoluble cavern debris so the pressure-volume relationship remains accurate.
Additional Information
- Mass is computed from the real gas equation m = (P·V)/(Z·R·T) using the hydrogen-specific gas constant (4,124.187 J·kg⁻¹·K⁻¹).
- Cushion gas equals the mass present at minimum pressure; working gas is the delta between maximum and minimum operating states.
- Optional compressibility lets you incorporate non-ideal behaviour from reservoir simulations or high-pressure lab data.