Gas depletion
For any new gas well, it is rare that any additional compression is needed for gas extraction. For a reservoir containing holding gas at a pressure of 1,000 psi, for example, a choke valve and compressor are installed at the surface connecting to the 500 psi gathering pipeline although not necessarily at the same time.

During the early years of production, the choke valve is used to throttle back the well pressure level to the line pressure level. When the well head pressure eventually drops below the line pressure, the compressor and choke valve arrangement is needed to continue secondary recovery.

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