Figure 2—2 shows how high pressure gas from the tubing side of dual completion can be employed to compress the low pressure casing gas. An ejector, an apparatus in common use in process plants, acts as a compressor without moving parts. The installed cost of the apparatus pictured in figure 2-2, is less than $10,000, and there are no operating costs. Use of an ejector in this service requires that both the tubing pressure and flowing gas volume be much higher than the collection header pressure and the casing gas flow, respectively. Note also, that the ejector must be protected against the errosive sand produced form the well.
Gas leaking into, and pressuring up, the casing of a partially depleted well must be bled down periodically. A W line connecting the casing to the tubing will permit this gas which slowly accumulates in the annulus to be recovered for sales instead of being vented to the atmosphere.