Well, first you walk down a deserted beach, then you find a "bottle" that might contain a genie, then you rub the bottle ... you know the rest.
The definition of "easy" is "someone else has to do it". Finding a "small inexpensive separator for shallow gas wells" is just not happening. This is the kind of activity that makes my living, because so many production engineers spec "just a separator" and then when the pipeline rots out or the transporter shuts the well in because of out-of-spec gas they finally call someone with experience in the field and the recomendetaion usually starts with "who sold you that crap?"
You didn't specify your expected gas/water/oil rates, anticipated line pressure, anticipated gas temperature, or whether or not you're anticipating wellhead compression.
I see a bunch of wells these days that have 3-10 bbl/MMCF of total liquids and gathering pressures under 20 psig with 120F reservoir temperature. If you do that math, you'll see that the entire liuid stream will move as a vapor that will not even slow down in a mechanical (or centrifigual) separator. In that case I often recommend not installing any tubing in the well or separation on the surface.
If the math works out that you'll produce significant liquid to surface then you need to do some real math to size your vessels appropriate to the task at hand. This isn't hard, it is just a task that often gets skipped when people are "doing their engineering off the surplus list" (e.g., put a 16-inch, 1,000 psi vessel with 2-inch nozzles on a well that really needs a 36-inch 280 psig vessel with 6-inch nozzles because "there's one in the yard").
I covered many of these issues in my February 27, 2006
Oil & Gas Journal article on the difference between artificial lift and deliquification. I've got a companion presentation to that article on my web page (below). I always try to get people to manage reservoir performance from the burner tip to put appropriate equipment at ever step from the wellbore tubulars through the final sales meter at the customer's plant. Don't skimp on a simple piece of the kit because it is "just a separator".
David Simpson, PE
MuleShoe Engineering
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