Gas behaves differently from fluid therefore you cannot use a simple hydrostatic formula to determine reservoir pressure. Gas is compressible but fluid is incompressible.

The formula to determine the bottom hole pressure of dry gas well is shown below;

Where; **Pbh** = bottom hole pressure in psia (absolute pressure)

**Pwh** = wellhead pressure in psia (absolute pressure)

**H** = true vertical depth of the well

**Sg** = specific gravity of gas

**R** = 53.36 ft-lb/lb-R (gas constant for API standard condition air)

**Tav** = average temperature in Rankin (Rankin = Fahrenheit + 460) Continue reading