wellhead choke valves 3

[hassann]

I have some confusion regarding the choke valves on oil and gas wellhead.
A. Choked flow is a limiting condition where the mass flow will not increase with a further decrease in the downstream pressure environment for a fixed upstream pressure and temperature.
B. On the oil and gas wellhead and production facilities, decreasing the downstream of choke valve pressure (for example decreasing pressure on the production separator) can be caused the increasing the mass flow rate.
I think A and B are completely contradictory to each other.
Please share your ideas as possible.

 

[GBTorpenhow]

A and B can both be true if the flow through the choke valve is not actually experiencing choked flow.

 

[TiCl4]

Choke valve is a descriptive name, not an indication of fluid status.

Choked flow is a function of the critical pressure ratio of the fluid. If the choke valve is not inducing a pressure drop greater than the critical pressure ratio, then no choking is experienced.

 

[1503-44]

A "wellhead choake valve" only restricts, or "choakes", flow from the well. The flow may or may not be "choaked", in terms of maximum flow.

Reducing pressure downstream of any valve may cause choaked flow to occur, no matter what kind of valve it is. That depends only on the pressure drop across the valve and how open, or closed it may be at any given moment.

--Einstein gave the same test to students every year. When asked why he would do something like that, "Because the answers had changed."

 

[hassann]

This is the actual experiment in the one of the oil production platforms:
choke valve upstream pressure 70 barg,
choke valve down stream pressure 11 barg, it shows that flow is choked.
separator pressure 10.7 barg, -separator is near the wellhead-
In the field, after decresing the separator pressure, the inlet mass flow rate of separator had been increased!
We repeated this experiment many times and the results were the same. As the pressure of the separator increases, the mass flow rate decreases,and with decreasing of pressure of the separator, We could see the rising of the mass flow rate!
I am trying to sat that the flow was choked, however we encountered with changing of mass flow rate with changing of pressure in downstream! My question is, why does the actual experiment contradict the laws of thermodynamics?
thanks for any respond.

 

[EdStainless]

If lowering downstream pressure increases the flow that much then you aren't choked.
Go back and check SG, temps in and out, flow rates, and so on.
Thermo never lies.


= = = = = = = = = = = = = = = = = = = =
P.E. Metallurgy, consulting work welcomed

 

[georgeverghese]

Choke or sonic flow conditions apply to gas flow, but not to all liquid flow. In this oil well, flow upstream may be mostly liquid (?), two phase flow conditions downstream.
There is some discussion on the topic of choked two phase flow in Perry in chapter on fluid flow - see page 6-29 in the 7th edition.

 

[1503-44]

See Petrowiki on the 2 phase stream.

https://petrowiki.spe.org/Flow_through_chokes

And

https://www.academia.edu/16121401/P...low_Boundary_and_Mass_Flow_Rate_Across_Chokes

--Einstein gave the same test to students every year. When asked why he would do something like that, "Because the answers had changed."

 

[hassann]

Dear all
I think i found the solution of this paradox or ambiguity.
we missed an important issue. In all thermo books, upstream of the nozzle (or choke valve) is a reservoir (zero velocity) . all fomulas for choked flow are applicable when upstream of the choke valve has zero velocity. but in the actual oil /gas wellheads,there is not zero velocity on upstream of choke valve and also reservoir is far from the choke upsteram. in the other hand in spite of thermo books ,in actual, choke valve has not been connected directly to reservoir. for this reseons increasing /decreasing of separator could cause variation of flow rate inspite of choked flow. therefor i think there is no any conflict between thermo and our expriment (becauce the velocity upstream of the choke valve is not zero.
I would appriciate share your ideas as possible.

 

[hassann]

Thermo never lies.

agree. based on above post.

 

[hassann]

georgeverghese (Chemical)

Could you please give a brief explanation in a few lines about two-phase choke current?
Choke does not occur in two-phase flow?

 

[hassann]

1503-44 (Petroleum

i appreciate sharing the references.

 

[hassann]

...flow upstream may be mostly liquid...

yes. there is mostely liquid. what is you idea about zero velocity upstream of the choke valve?

 

[LittleInch]

Hassann,

There are many different types of "choke valve" and trims.

Some of the plug and cage types have multiple trims one inside the other to avoid choked flow.

Without knowing what type of valve and trim you have you won't get anywhere here.

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

 

[GBTorpenhow]

A zero velocity reservoir upstream is not required for choked flow behavior, likely just an easy way to show the math for a book example. Relief valves, control valves, and regulators often show choked flow behavior with considerable upstream piping velocities.

You aren't choked because of the liquid phase present, most likely. Classical choked flow behavior is seen in single phase compressible fluids. Two phase gets more complicated.

 

[hassann]

A zero velocity reservoir upstream is not required for choked flow behavior, ...

I completely agree. I want to say that because the speed above above choke valve is not zero; The pressure changes in the downstream of choke valve could caused the pressure changes in the upstream of the choke valve even in the choked flow regime. therefore the mass flowrate is not constant.

 

[GBTorpenhow]

The pressure changes in the downstream of choke valve could caused the pressure changes in the upstream of the choke valve

This is just a fancy way of saying that the flow isn't choked. In choked flow, it is not possible for downstream conditions to be communicated to the upstream.

 

[Compositepro]

Choked flow means that sonic velocity has been reached in the flow and thus cannot be any faster. But if the density of the fluid entering the choke gets higher, the mass flow will increase.

 

[hassann]

GBTorpenhow (Mechanical)

please let me to complete your sentence: In the choked flow, it is not possible to inform the downstream conditions to the upstream if upstream conditions are constant. For example, when a psv is opened; At first, the flowrate is high and gradually decreases. Because the pressure upstream of psv is decreasing.

 

[GBTorpenhow]

please let me to complete your sentence: In the choked flow, it is not possible to inform the downstream conditions to the upstream if upstream conditions are constant. For example, when a psv is opened; At first, the flowrate is high and gradually decreases. Because the pressure upstream of psv is decreasing.

I think I'll stick by my statement. In choked flow, flow is constant if upstream conditions are constant, but even if flowrate is changing due to upstream conditions, there is still no way to communicate downstream condition changes back upstream through the sonic flow.

In your example, the conditions downstream aren't in any way impacting the flow or pressure upstream, the mass flow depleting the source of upstream pressure is. Repeat the example with everything exactly the same except for the downstream pressure and temperature and you will get the exact same response in the choked regime.