A plunger-lift system is a low-cost, efficient method of increasing and optimizing production in oil and gas wells, which have marginal flow characteristics.
Functionally, it provides a mechanical interface between the produced liquids and gas. Using the well's own energy for lift, liquids are pushed to the surface by the movement of a free-traveling piston (plunger) traveling from the bottom of the well to the surface. This mechanical interface eliminates liquid fallback, thus boosting the well's lifting efficiency. In turn, the reduction of average flowing bottom hole pressure increases inflow.
Plunger travel is normally provided by formation gas stored in the casing annulus during a shut-in period. As the well is opened and the tubing pressure allowed to decrease, the stored casing gas moves around the end of the tubing and pushes the plunger to the surface. This intermittent operation is repeated several times per day. Plunger-lift is especially appropriate in these four applications:
Eliminates liquid loading. As production velocity drops, wells tend to be less efficient in carrying their own liquids to the surface. The introduction of a plunger in this type well reestablishes the original production decline curve, increasing the economic life of the well. At the same time, it generally reduces the volume of injection gas required.
Can increase the economic life of this type well. By producing the well in an intermittent fashion, the well's own energy can be used. The need for other, more costly, lifting options can be eliminated.
Most intermittent gas-lift wells suffer from liquid fallback. This fallback tends to increase the average flowing bottom hole pressure, thus reducing production. With the plunger serving as a mechanical interface, liquids cannot fall back, but are all brought to the surface.
Most plungers have sealing elements that make contact with the inside walls of the tubing. As the plunger travels from the bottom of a well to the surface, the tubing is kept wiped clean, therefore eliminating the buildup or accumulation of paraffin, hydrates, scale, etc.
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