When you said ( hydraulic pressure ), Do you mean hydrostatic pressure ?
Pressure @ any elevation inside the well depends mainly on the fluid level inside the well & casing head pressure.
Casing head pressure is caused by the trapped gas in the casing between fluid level & well head.
For static wells :
pressure @ any elevation inside the casing
hydrostatic pressure of liquid existing above this elevation
CSG head pressure
concerning dynamic wells, I am not sure if this equation is applicable, or other factores affect the pressure.
hydrostatic pressure of any liquid column = density x 9.81 x column height
Any corrections on my words r welcomed.
I hope I could help you.
Forum administration member
Petroleum engineering B.Sc
3-2010 : 3-2011
Assistant petroleum production consultant
3-2011 till now
Well completion & workover supervisor