Gas and oil wells that are nearly depleted are often abandoned. Even though considerable amounts of gas and oil could still be extracted. The remaining oil and gas can no longer be recovered efficiently and cost-effectively with conventional methods. The well gas pressure is not enough to transport produced gases or liquids upwards through the production tubing.
In order to facilitate the production of mature gas fields, a possible solution is installing compression. By introducing compression, the well head pressure is reduced allowing larger gas flow rates. Wellhead compression (WHC) is the solution by which a compressor acts locally over one or a number of wells. As a result, the back pressure for a number of selected wells can be reduced. WHC extends the life of oil and gas wells and boosts their production output.
A conventional wellhead system uses either small, individual wellhead compressors or large central units handling several wells or an entire field. The small compressors can be as small as five horsepower. The large central units can be several thousand horsepower. These compressors need to have a relatively low capital costs and operate reliably more than 95 percent of the time.
The nearer the compressor is to the wellhead, the more likely the gas will be saturated. Some tolerance of this liquid is desirable in the design of a field unit. The standard machine should be capable of wellhead gas compression of as much as 2 percent H2S without serious corrosion problems. Reciprocating compressors are generally utilized in gas-gathering applications. Some rotary positive units are used in low-pressure applications, and both can be used as wellhead gas compressors.
In natural gas wells, the increase in gas velocity made possible by the use of a wellhead compressor system. This system eliminates a drop in pressure at the bottom of the borehole, eliminating production constraints due to liquid loading.
In oil wells, wellhead compression units reduce the pressure on pipes. They also largely preclude the development of backpressure which could impair production. Problems with air entrapment no longer occur, and the pump's delivery rate increases.