Wellhead flowline hydraulic

[e43u8]

Hi,

Is the wellhead flowlines, handling multiphase oil and equipped with choke flange/choke valve, being normally designed such that the relevant flow to be in critical condition in order to not being affected by pressure flactuations at downstream?

 

[LittleInch]

Not that I've ever seen.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[e43u8]

Please see the content of the following link:

https://petrowiki.org/Flow_through_chokes

 

[LittleInch]

Your talking about chokes not flowliness, that's what is confusing me.

Chokes are usually for high pressure so critical flow is normal.

What exactly is your question/ issue

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[e43u8]

I'm asking, as mentioned in the link i provided, if the flow in flowlines terminated to a manifold has to be always critical?

 

[e43u8]

Any comment from others...?

 

[LittleInch]

I repeat, the flow in the flowline is not critical. It is the flow through the valve that is critical.

And no, there is no requirement to make the pressure drop across a choke valve always in the critical zone, but if you don't then back pressure from the manifold would impact on flow.

Perhaps if you gave some examples or numbers or something then we could see where you're coming from.

At the start of a filed, especially say a gas field, the flow might start off critical in a valve ( say 300 bar to 50), but then as time goes on and the FWHP dies, then you could end up at say 80 / 50 and then an increase in pressure of the manifold starts backing the well out.


Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[e43u8]

Thanks LttleInch,

Regarding the example refer to the one included in the link i provided...

You are right as the time goes the wellhead pressure decreases such that there would be no critical flow through the choke...

But i want to know if the flow through the choke at the start of an oil field has to be designed for critical, as the wellhead pressure is mostly more than two times of the choke downstream pressure?

 

[LittleInch]

It has to be designed for your particular circumstances.

In many cases the initial WFTP will be a lot higher than the downstream manifold needs to flow the well products to the processing facility, but not always. If that is > critical pressure then that's what you design the choke for, if it's not you don't. There's no "have to" here.

Unless you can provide some actual proper examples, not a petro woki page, I think we're going round in circles here.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[e43u8]

The oil wells have a maximum pressure of 1000 psia and the manifold is located around 5 km average far from the wells. The downstream separator operating pressure located after manifold is to be set around 20 barg and the flowlines are to be set having 8" size.

But at first i am going to know if the design flow through the chokes of such flowlines would basically set to be critical to avoid flow variation due to pressure variation at downstream?

 

[LittleInch]

In this case yes, flow in the choke is critical flow.

the flow variation bit is a bit overdone here as the arrival pressure should be maintained at a fairly fixed level.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[e43u8]

Please clarify your second sentence about flow variation...

If the flow across the chokes of flowlines would be critical, does it nedded having FCV at downstream before manifold (as it has considered by client in relevant design basis)?

Can you explain, in brief, the design basis of choke flange sizing in such flowlines?

 

[LittleInch]

A choke valve is a control valve by another name.

It's just a control valve designed for pretty brutal service.

To add another control valve is just a waste of money.

Copy or sketch the relevant bit of the P&ID, but is sounds like some one doesn't really understand what they are talking about.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[e43u8]

A choke flange with a fixed orifice area, which is applied in the system i am describing, isn't really a type of control valve.