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