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Successfully modeling multi-phase flow in surface gathering lines

Successfully modeling multi-phase flow in surface gathering lines

Successfully modeling multi-phase flow in surface gathering lines

(OP)
Hello, I'm new to the site, so I thought I'd try to at least see if anyone had any advice on this ...

What I am wondering about is what tools and methodologies other oil and gas engineers might have utilized in an attempt to model multi-phase flow characteristics in a network of surface gathering lines.

I'm still trying to get my head wrapped around what is physically happening in this system in order to use some of the commercial modeling tools I have... but I fear that without the ability to correctly model accumulation of heavy liquid hydrocarbons and subsequent reduction in effective pipe diameter any network modeling tool I have will not produce desirable results.

Basically what is happening is, we have wells in our system that make water, and our gas stream is fairly rich (%91 methane, %9 C2 and heavier lets say) ... most of this system resides on the surface and daily temperature swings can be quite wide, say 0 degrees to 60 degrees depending on the weather.

I am relativley certain that a portion of the heavier hydrocarbons are liquefying during the night when it is cold and flashing off when the sun hits during the day ... What I am floundering on is modeling the accumulation and subsequent pressure increase in the system when this mass of heavier hydrocarbons vaporizes again ... Meaning, we might go from a 50 psig line pressure to a 150 psig line pressure over the course of 4 or 5 hours during the day.

Please offer any advice, thanks.

 

RE: Successfully modeling multi-phase flow in surface gathering lines

Modeling multi-phase flow is a very difficult and imprecise exercise.  The high-dollar multi-phase models don't do a very good job mostly because they assume a specific flow regime and don't change flow regimes as fast as the line does.  For people working with real problems in real systems, I recommend saving the cost of the much-touted multi-phase programs.

On the other hand it looks to me like you are trying to determine the "clean line" pressure drops so that you can see when you've had liquid accumulation that is hurting well performance.  That is a useful and very achievable goal.  Most commercial programs will predict the wellhead pressures in the gathering system very well.  When I was operating a gathering system I had a model that I would run each month with a currenet, instantaneous flow rate from each well and an off-system delivery pressure.  Wells that were too far ("too far" is a subjective value that you need to set for your system) off the dry-theoretical pressure caused a reevaluation of the pigging schedule on that line.

At the end of the day, the only intervention you have is to pig the line.  Knowing that your 100 psig pressure swings are caused by liquid accumulation is kind of worthless information if you don't do something about it (and you can't prevent the liquid accumulation, many people have tried and none have succeeded).  The model can tell you to run pigs, but that is about all.

David

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