Wellhead Compression – Transient Effects

To further complicate the adjustment of a field compressor, one needs to be aware of certain transient effects that the well imposed on the compressor.
• Many wells, immediately after unloading liquids exhibit an increase in wellhead pressure sufficient to overload and stall the engine.
• Opening the head-end cylinder clearance valve to reduce the first-stage discharge temperature will immediately increase this discharge temperature and can trip-off the compressor. However, once the wellhead pressure rises due to less gas being moved, the head-end discharge temperature will drop.
• After switching a compressor from single-stage to tandum operation, the second-stage discharge temperature will tend to increase for a few days as the wellhead pressure drops. This often leads to compressors tripping off unless corrective action is taken.
• The immediate effects of soap-sticking a well (i.e. unloading liquids by adding a foaming agent into the well’s tubing) may be to over-load the engine due to excessive suction pressure.
• A compressor which has operated properly in a tandum mode is shut-down for maintenance and thereafter repeatedly trips off on high discharge temperature. The problem is that the well has loaded-up with liquids and the resulting low wellhead pressure is causing too high a compression ratio.

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