choke valve in gas injection line 4

[pipexp]

In one of the offshore platform I found that in gas injection line choke valve is installed before pressure control valve in series. I think choke valve and flow control valve in parallel is better option in gas injection line. Can any body suggest other better options in the system?

 

[MortenA]

One should always remember that pressuredrop is pressuredrop. A valve does not "know" that its a flow and not a pressure control valve and does not have different operation anyway.

I assume that flow control is needed because the injection gas i routed to several wells at a time.

The flow control valves should actually then mean that the pressure drop in normal operation across the choke should be very minimal. Anya additional pressure drop across the choke is actually just unrequired work for your compressor (although is may be required for other reasons).

I dont really understand the "parallel" idear. If you mean that one well have and a second the flow control valve - this will work fine. Off course there will be only one well with the choke and the rest will have the flow control.

Best regards

Morten

 

[zdas04]

It is very common in a gas-lift configuration to use a very-high pressure header and take gas off at a reduced pressure. In that case you may be taking too much pressure drop for a single control valve to properly handle (they stand up better if your normal conditions are above 25% open) and a choke is commonly put upstream to take the first pressure reduction and allow the control valve to actually be in a range where it will work best.

Putting them in parallel would be a very bad idea because then each one would have to take the entire pressure reduction and your choke would have to be much smaller (more risk of cutting it out) and your control valve would have to be much further shut (again, increasing the amount of errosion).

David Simpson, PE
MuleShoe Engineering

http://www.muleshoe-eng.com

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

The Plural of "anecdote" is not "data"

 

[MortenA]

David

I agree with you with regards to having both a choke and a parallel flow for each well. This would not be a good idear.

Best regards

Morten

 

[brainstorming]

While I don't understand much in your field but I would suggest the parallel configuration provided that (if I am not wrong) chock valve can be used in some cases not normal operation.
this will save power if a compressor is located downstream !!

Regards

 

[DrillerNic]

In most gas lift systems you want to control the gas lift flowrate, and the injection pressure is what you get from the compressor (higher is always better as then your gas injection point is lower, resulting in more production, and youe usually stratching around trying to get more pressure for the same flowrate). So strictly speaking, a flow control valve is all you need (I've seen several gas lift system on different fields and platforms with a flow control valve only).

I'd say that if you've got an oversized compressor (giving you more pressure than you need to inject at the lowest gas lift valve), then you're very lucky (!!!) and you'd use a choke to drop the injection pressure to what you want, and then a flow control valve is series to get the flow that you want.

 

[MortenA]

Actually his not asking about gas lift but about injection. The problem is however the same - allthough the chance of having a compressor that is oversized to mee seems smaller

Best regards

Morten

 

[pipexp]

MortenA(Petroleum)

Thanks

I actually wrote about gas injection that is used as gas lift to increase oilproduction from wells.In this case pressure at the injection header is about 81 Kg/cm2 and pressure at inlet of well is about 65 Kg/cm2. And flow line is 2" size.

By the word parallel, I mean that, the operator has the option to flow to different wells either through flow control valve or through choke valve.

Regards

nirmalii

 

[MortenA]

allright my mistake. I would usually think that "gas injection" is where excess gas is re-injected into the reservoir. This is frequently done in the North Sea - allthough many places you just flare it.

Gas lift is gas lidt.

To me it then seems that you are looking for a system where you control the flow fairly accurately to n-1 wells - and then the last (with the choke) takes the excess.

Best regards

Morten

 

[DrillerNic]

nirmalli- well, you're a very lucky person to have more gas lift injection pressure available than you need! Why is the inlet pressure limited to 65kg/cm2? Is this due to a pressure rating? After all if the pressure is too much you just push the fluid level in the annulus below your lowest lift point....

I wouldn't recommend putting two valves in parallel, (too much cahce of the operator altering the wrong valve and changing the gas lift flow rate which is critical), but just fit flow control valves and then if you need to drop the pressure further, put a fixed choke in series.

By the way, if you're lifting lots of wells off one common gas lift manifold, do you model your gas lift gas allocation accurately? It's the kind of thing my company is alway doing- building Integrated Asset Models- and there's often a healthy increase in production....

 

[pipexp]

DrillerNic(Petroleum)

Thanks,

In fact there is no limitation to inlet pressure for the wells. Actually inlet pressure for individual well is limited by requirement of lift gas for that particular well for economical production from the well. There fore, in one platform there may be different wells with different gas injection pressure. Flow rate for a particular well is deceided by production engineer of the platform.

nirmalii

 

[DrillerNic]

nirmalii-

How does the production engineer on each platform decide the gas lift gas flow rate to each well? That was my question. In my company's experience, building an accurate model of a network of gas lifted wells, and modelling all the wells together, incorporating the inflow/ outflow modelling for each well, in addition to the surface lift gas flowrate modelling, (and even including reservoir modelling too if you can) into one single model almost always results in more production. There has been some startling reuslts- on one field the recommendation was to shut in all but one well until more gas was available. The model predicted that the one well would produce more oil than all the other wells combined, if that one well recieved all the lift gas that was available....and it did, when the oil company followed the recommendation!