Simple solutions often work best. Plunger lift is a simple and economical artificial lift system for natural gas wells. It is ideal for wells in which natural depletion has fallen below critical flow rate or for wells with high accumulations of solids such as sand, salt, coal fines, paraffin, and scale.

Self-regulating plunger lift systems are economical and easy to install and maintain. (Images courtesy
of Production Control Services)

However, plunger lift alone might not be enough to effectively remove liquids in particularly deep wells or wells with low gas and high liquids (in other words, a low gas-to-liquid ratio, or GLR), such as gassy oil wells. A pumpjack unit often is prescribed, but plunger lift is more economical.

For these wells, multistage plunger lift is a cost-effective alternative that has produced impressive results. It is not only effective but significantly less expensive than pumping units.

A multistage tool essentially creates multiple plunger lift systems in one well. The tool allows the liquid load to be lifted in stages and enables the well to use its own energy to remove large or heavy liquid accumulations more efficiently.

Multistage plunger lift works like a modern-day bucket brigade
The multistage tool is placed by wireline roughly 40% to 70% of the way down the tubing above a plunger lift system installation, typically comprised of a bottomhole bumper spring with a plunger above it. A second plunger is set on top of the tool.

The system operates like a conventional plunger lift system. During the first cycle, the lower plunger carries fluids up the tubing and delivers them to the multistage tool. They flowthrough the tool and are held above it by gas flow. Upon shut-in, the ball check in the tool engages, retaining the fluids until the upper plunger falls from the surface, settles through the liquids, and lands at the tool. Simultaneously, the lower plunger falls back to the bottom.

During the next sales cycle, the upper plunger delivers fluids to the surface, while the lower plunger delivers more fluids to the tool. The plungers work in tandem in subsequent cycles. In this way, the multistage tool acts like an intermediary standing valve. This process lifts smaller liquid loads more frequently in stages, allowing the well to more efficiently use its own energy to remove liquids and increase productivity.

Easy, economical alternative to pumpjacks
A pumpjack (also known as a sucker rod pump, beam pumping unit, etc.) is a common artificial lift device that is powered by fossil fuels or an electric motor. It requires a large up-front investment in equipment, and installation and maintenance costs can be high.

Typically, a plunger lift system with the multistage tool costs about one-tenth that of a pumpjack. A plunger lift system does not require expensive equipment or a power or fuel source; it is an entirely mechanical system that uses the well’s own energy to operate. A multistage plunger lift system is much less expensive to install, operate, and maintain over the life of a well.

Pumpjack candidates now successful plunger lift wells
A well with a plunger lift system already in place with the bottomhole bumper spring set at 8,169 ft (2,487 m) was no longer able to lift fluids on its own. The plunger cycled, but because of the large amount of liquid, long shut-in times were required. By the time the plunger was able to run, the tubing pressure was greater than 800 psi, which knocked down the separator.When it would cycle, the well was able to produce roughly 17 Mcf/d of gas and 12.6 b/d of liquid. A pumpjack was considered, but the cost was prohibitive given the marginal production.

A multistage tool was installed into the existing plunger lift system. The total system was approximately US $4,000, including the existing plunger lift equipment, the new multistage tool, and the addition of a second plunger. The tool was set at 4,872 ft

A multistage plunger lift downhole tool is shown in its open position with key components labeled. It is landed in tubing halfway down the well after the conventional single-stage plunger is landed near bottom.

(1,485 m), with a dual-pad flow-through (bypass) plunger below it and a padded plunger above it. The tubing pressure was 1,460 psi, and the casing pressure was 1,510 psi.

After a couple of cycles, the pressures dropped enough so the separator was able to function and constant production was achieved. The cycle times were fine-tuned, and the well was able to produce 106 Mcf/d of gas and 37.7 b/d of oil.After one month, production leveled out and remained at 124 Mcf/d of gas and 12.6 b/d of oil.

Another well that was unable to lift liquids also was producing significant frac sand and wax. The bumper spring was set at approximately 8,136 ft (2,480 m). The starting tubing pressure was 200 psi, and the casing pressure was 1,000 psi. Because of the amounts of fluid, wax, and sand being produced by the well, the plunger would not cycle consistently, and the well was shut in the majority of the time. Pumpjack installation and chemical injections were being considered.

Instead, a multistage tool was installed into the existing plunger lift system. The tool was placed at approximately 5,085 ft (1,550 m), with a solid flow-through plunger below it and a solid ring sand plunger above it. By this time, the well’s tubing pressure had increased to 250 psi, and the casing pressure increased to 1,200 psi. During the first few cycles, the sand production was challenging. As the casing pressure came down, the well produced more and more sand, causing the bottom plunger to stop cycling and the top plunger to wax off.

Pulling the multistage tool by wireline and cleaning the tubing decreased sand production. The plungers were able to cycle regularly, keeping the tubing clean and prohibiting wax buildup. The initial production was high for a typical plunger lift system at 70 Mcf/d of gas and 37.7 b/d of oil. Production then slowed to its current rate of 42 Mcf/d of gas and 8.8 b/d of oil.

Plunger lift is not expected to be successful in wells with a 1:1 gas-to-fluid ratio. However, the addition of a multistage tool can generate significant production increases in these wells.