The change in pressure (pressure gradient) of a fluid column per unit of true vertical depth.
Normal hydrostatic pressure gradient of popular petroleum fluids at Standard Conditions
| Fluid | Normal density range | Hydrostatic pressure gradient range | |
|---|---|---|---|
| g/cc | kPa/m = bar/100m | psi/ft | |
| Natural Gas | 0.007 – 0.30 | 0.69 – 2.94 | 0.003 – 1.130 |
| Gas Condensate | 0.200 – 0.40 | 1.95 – 3.92 | 0.090 – 0.174 |
| Oil | 0.400 – 1.12 | 3.92 – 11.0 | 0.174 – 0.486 |
| Water | 1.000 – 1.15 | 9.81 – 11.28 | 0.433 – 0.500 |
The most common value of hydrostatic pressure gradient is ~ 10.1 bar/100m which corresponds to rocks saturated by 1.03 g/cc density water.
Formation pressure at a given depth calculated with hydrostatic pressure gradient is called Hydrostatic pressure.
If the actual formation pressure is more than 10% higher than hydrostatic pressure then it is called anomalously higher pressure deposit.
If the actual formation pressure is more than 10% lower than hydrostatic pressure then it is called anomalously low pressure deposit.
See Also
Petroleum Industry / Upstream / Petroleum Engineering / Subsurface E&P Disciplines / Reservoir Engineering