5 replies to this topic

[Jiten_process]

Hello everyone...

This question is regarding the natural gas flow from gas wells.

There is 65kg/cm2(g) natural gas coming from gas wells with approx. flowrate 0.01MMSCMD (million standard cubic meter per day). The pressure of this gas needs to be reduced to 15kg/cm2(g). We are thinking of to use choke valve for above application since it is being used in existsing facility.

Now our client is asking whether we can use angle choke valve instead of horizontal choke valve due to dilivery issue.

my questions are
1) what is the difference between horizontal inline choke valve and angle choke valve and what difference it makes in design and operation?

2) anybody has experience of using choke valve in similar application? prons and cons of it?

Plz suggest...

[JoeWong]

Gas from well potentially contains sand particle and it is erosive. Choke valve with harden trim and large body (induced low velocity) is normally used for throttling the well flow.

This question is best answer by choke valve supplier i.e. MOKWELD.

[Art Montemayor]

Jiten:

Funny you should mention choke valves. I have just been working in applying them on an offshore platform. Attached, you will find specific information on the type and model of choke that I have had a lot of success with and would recommend.

A choke is usually employed as the angle design because it has been found to be more convenient in its installation out in the field in gas and oil well production applications. The resulting mixed phase, low pressure product of the choke valve is usually headed to a processing unit or a separator and the choke valve is traditionally located immediately prior to the target. Therefore, a 90 degree angle is preferred in order to facilitate the inlet and outlet of the choke valve with easy access to its handle.

I hope this helps out.
 Cameron_Willis_Choke_Valves.xls   532.5KB   389 downloads

[aliraza]

Dear Jiten,

I have sized and select the choke for my natural gas processing project. Choke is located at the well head dropping the pressure of 1600 psig down to 1000 psig. And it is designed on maximum flow of 35 MMSCFD. That choke is 90 degree angled.

I must second Art's comments that angle choke is easy in installation. Choke basically drops the well head flowing pressure from its upstream connection down to the required operating pressure at downstream of its connection. But it regulates the flow within your mininum and maximum flow rate by keeping the operating pressure same.

For example in my project I can regulate the flow rate within 15 MMSCFD and 35 MMSCFD at its fixed 1000 psig operating pressure at downstream only in that situation when I am having volume more than the operating flow rate at the upstream of the choke.

And that's how a flow rate is controlled through a choke. And one more important thing is that almost all the vendors recommend the choke with 60% open at its maximum flow rate.

Regards,

Ali Raza

[Jiten_process]

Thank you very much art, aliraza...

Now confusion is clear....actually i have never dealt with choke valve so that was the question. We have also consult some vendors WONK, TYCO, MOKWELD (suggested by joe)

that excel sheet was also very helpful to understand the choke valve.

neways thanks once again to all.

[ashetty]

Hello Jiten,

I happen to have a fair deal of experience with well head chokes,when i was working as production engineer for a gas production facility,so i thought i could contribute my 2 pence...in addition to the useful comments posted by the other members.
In my case what happened was that...our wells had started cutting water. Soon the water also started bringing in sand (which is the normal phenomenon in such a case).Soon the choke valves of 2 of our wells had failed. Subsequent investigation revealed that the choke internals as well as the casing body were severely eroded due to increased water and sand and also due to high differential pressure across the choke (high velocity with sand content/high erosion rate).
We could do well to keep in mind the that lead time for automated chokes is fairly long so failure of chokes invariabbly leads to downtime and loss of revenue.So (If possible)consulting the reservoir engineering about how the well/wells may be expected to behave over the lifecycle may be a good idea.
Next some care may need to be excercised while procuring the chokes.More realistically it may be wise to consider liquid/water production along with the gas which would ask for a greater Cv.If cost is not so much of an issue you may also allow some Cv upsides in future, because swapping of choke valves and other instrumentation or piping is not so uncommon in the oilfield.
Also make sure the vendor is well informed of water slugging & sand production problems (If any)
Last and most important, check the trim material .Almost always ...it has to be Tungsten Carbide.

Shetty.