The pressure upstream the choke valve

I would ask you to rephrase your question because I am not sure that I am understanding it correctly....

but there is significant pressure drop between the reservoir pressure and the choke valve. Line losses are present in every section of the piping, casings, though the christmas trees etc. So yes the resevoir pressure should be significantly higher than a point just upstream of the choke valve, then there is pressure drop after the choke valve through the piping as well.

Part of my confusion with your question is where exactly in the system are you measuring 309 barg? And why are you concerned about it?

Hi Heita

so what I am concerned about is that, is this pressure constant all through the way -coming from the reservoir all through the casings and then the Xmas trees and reaching the choke valve-?

Well, yes it will be provided that the choke valve is closed and there is no flow in the upstream line elsewhere!

No flow = no pressure drop = constant pressure = 309barg back to source!

Hope this confirms your suspicions!

Hi Beej50

But the choke valve is not closed! Choke valve is there suddenly reducing the pressure from 309 barg to 139 barg. So there is a flow through it.

I just don't get this point: We keep saying the pressure upstream the choke valve is 309 barg and downstream it, is 139 barg. as for the lines at the downstream, it is understandable, 'cause the pressure is kept constant through the different vessels used, but for the upstream part I don't see how the pressure is kept constant!?

Hi Heita

OK then, if you have any flow through the choke valve (that I am now taking as a Pressure Reducing Valve) you will have sustained pressure drop upstream coming towards the choke valve and arriving at it, at 309barg. This means that the pressure way, way upstream of the choke valve must be a measurable amount above 309barg!

This also means that the pressure downstream of the choke valve will not be universally at 139barg as the same sort of restrictions and pipe losses will be occurring!

P > 309barg............P @ 309barg....Choke Valve....P_R @ 139barg.........P_R < 139barg

If you see what I mean!

Regarding any two points along the piping system, the pressure will be varied from point to point. The pressure at downstream point will be lower than the pressure of upstream point due to the friction loss.

The amount of friction loss is a function of Reynolds Number which depends on the fluid and its kinematic viscosity, velocity, pipe material and its roughness, pipe diameter and flow rate.

I get it now!

Thank you all...

do not forget to add fluid head as you go under sea and down the tubing to the formation. Its probabilly 600 bar or more bottom hole.