1 reply to this topic

[ekar]

Dear Friends,

I am having a problem with pipeline hydraulic simulation and hoping to get some advice..

I am currently working on a pipeline hydraulic study of a gas lift line. The gas lift departs from the source platform (let's call it A) to the destination platform (let's call it about 6 km away through a subsea pipeline. Between platform A and B, the subsea pipeline resurfaces at platform C, which serves only as a transit platform. So from platform A subsea pipeline, the gas lift goes up the riser at platform C, into a topside piping, and down the riser again into subsea pipeline going to platform B. The gas lift is drawn from the compressor at platform A at around 650 psig, and once arriving in B, it goes to gas lift separator. The study itself is conducted in OLGA, as we want to simulate pigging and come up with slug volume, and lastly check the adequacy of the gas lift separator and its LCV. These are all existing pipelines and platforms over 15 years old.

The way we do it is to first validate the pressure information. We build a pipeline model from A to C and from C to B separately, having the actual pressure information on each platform. The resulting flowrate is then compared with the information on actual flowrate - if there is any significant difference, we may adjust the pipeline ID to match the actual flowrate, or just use the resulting flowrate, depending on client's input. The second step is to build a complete pipeline network model - from A to C to B - and run it at steady state mode. We expect the resulting pressure, temperature, and flowrate to be close to the validation model. Lastly, we will run the model at pigging mode.

The problem we run into right now is this - the flowrate obtained from the complete network model is different from the flowrate obtained from validation model - the first one is about 4.9 MMSCFD, while the one from validation model is about 4.2 MMSCFD. I cannot think of any valid reason why it is so, and the model parameters and input data have been correctly set. Could you please give your thoughts/advice on this...?

Actually, my colleague is dealing with a similar issue using PIPESIM (although for a different pipeline). Is this kinda common when doing pipeline simulation??

Appreciate any input you can give. Thanks!

=ekar

[ankur2061]

ekar,

Since you have already have a model in OLGA, I believe you possess a license for the same. SPT Group who are the licensors of OLGA should provide you the required services for resolving your flow assurance queries related to your specific problem. They are responsive and if you write a mail to them and maybe send them your model they might be able to clear your issues related to the variation in flow rate in the validation and network model. Following is the link to contact them:

http://www.sptgroup....ontact-offices/

Regards,
Ankur.