Gas Line, Worst Case Discharge 1

[Pmatherne]

I am trying to do a worst case discharge on a pipeline that is primarily gas. there will be a little bit oil compared to the gas in the system. 135 MMSCF and only about 5500 BOPD
The problem I am having is you have to take the volume of the pipeline, which is a 36" OD and over 360,000 feet long in the last leg when it come in from offshore. So I am coming up with a WCD over 80,000 bbls when the most the line will hold is about 30,000 bbls (Assuming it takes the gas 5 days to get to shore)
Does anyone know if there is an alternative version to use for gas pipelines

Future PE Engineer
Pet project I am working on to help other engineers, not much yet hoping to get it grow as I learn more

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[LittleInch]

I'm sorry, but I really don't understand what and why you're trying to calculate here. Also some of your figures look a little odd - a 36" line for only 135 MMscfd would seem to be very big, if this is also a two phase line this implies a lot of liquid hold up.

You don't say anything about terrain or slopes or pressure or velocities or how you've calculated any of the figure so far

You will need to explain much more and attach a few sketches / profiles if you're going to get sensible responses.

My motto: Learn something new every day

Also: There's usually a good reason why everyone does it that way

 

[Pmatherne]

This pipeline system has originally laid down in the 70's. Back then there was a rate of 510 mmscfd (from the paperwork I have been able to find). I do have a MAWP of 1200, but not the actual working pressure. The pipe is in about 37 feet of water at its deepest and gradually rises as it gets near shore
For the WCD, you usually take the volume of the pipe and the amount that can flow through it before the shut down valves close and isolate the system. In a pure liquid line this is pretty easy. Now when a portion of that pipeline volume is gas how can I get a good estimate on the amount of liquid that is still in the pipeline

Future PE Engineer
Pet project I am working on to help other engineers, not much yet hoping to get it grow as I learn more

http://www.peexamquestions.com

 

[LittleInch]

you need to run at the least a steady state two phase flow analysis using if possible the composition of your fluids, (liquid and gas), start pressure, end pressure, nominal SS flow rates and profile and it will calculate the amount of liquid hold up in the line. As your fluid progresses along the line the actual velocity and pressure will change quite a lot and hence the amount of liquid in the pipe changes for every km. averaging this doesn't work very well.

However unless your line is incredibly gently sloping in a continuous manner this will give a much higher figure than what could ever leak out as liquid generally doesn't like flowing up hill and will sit in the low spots.

You could find that the liquid in the line exceeds by some multiples of what your steady state rate is. Big lines running quite slowly can fill up with a lot of liquid. If your actual gas velocity drops much below 3.5 m/sec - 12 ft/sec then as a general start point you start to run into increased liquid hold up.

Is this closer to your issues?

My motto: Learn something new every day

Also: There's usually a good reason why everyone does it that way