Why bypass Feed Gas Compressor System until later years of operation 1

[enggirl2014]

Hi,
I am a student currently doing a coop at an oil/gas company and am writing my term paper on our feed gas compressor system. So I’ve done a fair amount of research but I still don’t understand why in the industry the feed gas compression system is bypassed until the later years when pressure is considerably lower. Does the system act as an aid for the gas compressing it to the higher pressure desired in the early stages? Why is a high pressure desirable to continue to the separator, does this just have to do with the designed operating pressure or is there alternate reasoning?
Thank you

 

[pmover]

a simple schematic will be helpful - avoids guesswork.

 

[enggirl2014]

Hope this helps.

 

[zdas04]

Every well has a pressure window that maximizes flow rate. Generally the minimum on that window is pretty high in the early days (I often find a sweet spot with flowing bottom hole pressure about half of reservoir pressure, which often gives me a flowing tubing pressure approaching 1,000 psig). If the compressor was designed to take 100 psig gas to 1000 psig (which is a pretty common range in midstream), then if I can get maximum flow with the compressor turned off there isn't much reason to burn the fuel to run it.

As reservoir pressures come down, that target pressure also comes down. Sooner or later the operating range of the compressor puts well pressure in the sweet spot and running the compressor makes sense. Some time after that, the required wellhead pressure will be too low for the main compressor to maximize production and we move compression out into the field. First nodal (or straddle or booster depending on your location) compression is installed and eventually well site compression is needed.

I wrote an SPE paper on this concept for a specific field a few years ago. It is kind of heavy on reservoir stuff but it might help you get your head around the idea of a "pressure window"

David Simpson, PE
MuleShoe Engineering

In questions of science, the authority of a thousand is not worth the humble reasoning of a single individual. ùGalileo Galilei, Italian Physicist