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# Flow pressure from Gas well

## Flow pressure from Gas well

(OP)
Trying to calculate total pressure/flow numbers for a well that is producing 7 mmscfd gas, 2000 bbld water, 600 bbld oil. All will be seperated and sent to an oil tank, water tank, and gas line. I know that my gas output line needs to be 200 psi. Trying to calculate the inlet pressure that will go into a separator so that I can size it. Calculating for a temp of 60 deg and against standard pressure. Just not exactly sure how to add/account for all gas, oil, and water volumes/pressures coming out of well. Thanks
Replies continue below

### RE: Flow pressure from Gas well

The water and oil volumes will not change much with only 200 psig. You need a couple of thousand psi and more than 10F to start seeing any real volume change in them, but I can show you how to do that if you need to.

There will be 2-phase flow in the pipe going from the well head to the separator, so the elevation of the pipe may make some difference in the type of flow you will get there and the pressure drop in that line.

Some other questions we should ask now are ...

Is it pretty flat between well and separator?
How far from well to separator?
How far from separator to gas pipeline?
How far from separator to tanks?

Do you have a gas meter after the separator in the gas pipe going to the gas pipeline?
Do you know the gas composition? Or ... do you know the gas specific gravity?

What is the pressure at the well head when there is no flow for a week or so. Closed off pressure? That should be the max possible pressure at the well.

What is the pressure at the well head when flowing 7MMD gas and 2600 bbls of liquids?
And the gas/liquid temperature?

What is the maximum pressure allowed in the gas pipeline?
What is the gas pipeline's operating pressure at the tie-in connection point?

Yearly high and low air temperatures?

### RE: Flow pressure from Gas well

(OP)
Thank you for the response. Right now the distance from well to separator isn't something that needs to be considered just because of where we are in the design. The gas composition isnt important either because this is just the first phase of separation between oil gas and water. I do not know the pressure at the well head when it is flowing with these values, thats what I am confused on and need to find. The gas temp is lets say 120 and liquid is 60. As far as pressures go, really the only thing that is "known" at this point is that the gas tie in (output) line is 200 psi.

### RE: Flow pressure from Gas well

You should get the well pressure at max and when flowing ASAP. You're kind of stuck without that.
Gas design pressure makes a big difference in equipment size. Temperature too, but not so much. The higher the pressure, the smaller the equipment. 1000 psi design will half the size of a 500 psig design. 500 psig design pressure will be roughly half the size of a 250 psig separator. 200 half the size of 100 psig. If pressure can be higher than 200, you could then let pressure down before going to the gas pipeline. Large differences in size occur at lower design pressures, so design pressure is kind of really important.

You could assume 200 design pressure, but that might wind up being 2x or more as big as you will need in the end.

If the well is too low pressure, you may even need a field compressor to get into the gas line.

Come back as soon as you know the well pressures and temperature, or otherwise determine the separator design P & T.

### RE: Flow pressure from Gas well

I agree with Mr 44.

This isn't something you can calculate.

You could work out the separator size based on the liquid flows but not the upstream stuff.

But this isn't a big well so you are probably OK with 4 or 6 inch pipes.

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

### RE: Flow pressure from Gas well

You only know the volume of liquid. The total volume of the separator is determined by the gas velocity and that you cannot know until the operating pressure is decided. The area of gas flow through the separator (basically the diameter) must be sized so that liquid/gas velocity and transit time is slow and long enough such that the liquids will actually separate as intended.

Speaking of which, I just assumed that the gas pipeline is a gathering pipeline system and that there is no strict requirement to have dry gas at the connection. If the gas pipeline carries dry gas, you will need a dehydration system too.

Also ensure that the gas pipeline authority will allow all your gas stream components to be injected. If you have too much N2, CO2, or H2S there are more problems to solve here, so at least get a handle on the stream composition.

### RE: Flow pressure from Gas well

True, but also residence time for liquid separation is a start point also and if you assume the liquid part take say 40% of the volume of the separator you're probably not far off.

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

### RE: Flow pressure from Gas well

(OP)
Thank you all for the responses! So assuming the design pressure is 200 psi, and lets say gas and liquid each take up 50% of the volume coming from the well and going into the separator. What are next steps in sizing/designing the separator process and piping size. Looking at using either a high pressure 2 phase separator followed by a heated 3 phase lower pressure separator OR a single 3 phase heated separator which would have to buy high pressure. Thoughts?

### RE: Flow pressure from Gas well

(OP)
I did some calculations using the design pressure and volume flow rates that I have coming out of the well. I was getting somewhere around 12 ft/s of gas flow with a 12 inch pipe when pumping against standard pressures

### RE: Flow pressure from Gas well

(OP)
Again, this is still pretty early in the design process. The goal of this part of the process is to do first stage seperation, the seperated oil, gas, and water will be transported in trucks to another facility for further treating. I know there are some unknowns but im really just needing to get more of a broad preliminary design done at this point with the values given.

### RE: Flow pressure from Gas well

Whoa! Slow the gas down.
Separator design

### RE: Flow pressure from Gas well

Maybe this helps

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