How can I calculate condensate amount that will condense at the seperator in a gas reservoir? I found a graphical method for the water that will condense at the seperator; is there a method for condensate too?
Retention times in a typical wellsite 2-phase separator are a fairly small number of seconds. Except in one very special top-hat separator I've seen, the outlet temperature and pressure are amazingly close to the inlet temperature and pressure.
So to answer your question - you will typically get zero condensation in a wellsite separator. If properly designed it will do a very effective job of removing liquids from the flow stream (typically down to 20 microns in largest extent), but water vapor or vaporized hydrocarbons tend to be 3-5 orders of magnitude smaller than that.
The chart you found (either GPSA 20-3 or a version of the Smith Chart) will tell you how much liquid will vaporize and be available to condense somewhere (usually in the least convenient possible location), but certainly not what will condense in your separator. Don't be a victum of wishful thinking.