Plunger lift is a way of keeping a gas well flowing by using its own pressure to sweep accumulated liquid off the bottom, and it runs as a repeating cycle. A free-traveling plunger falls to the bottom of the well, then the well's built-up pressure drives it back up carrying a slug of liquid above it, arriving at surface where a controller decides what to do next. Each cycle is a sequence of distinct phases - shut in, flow, and afterflow - and the plunger controller times those phases using pressure and plunger-arrival sensors. Tuning the cycle so it clears liquid without wasting the well's energy is what plunger lift optimization is all about.
Plunger Lift Cycle in one line: A plunger lift cycle is the repeating sequence a plunger-lift well runs through - shut-in to build pressure, flow to bring the plunger and liquid slug to surface, then afterflow to produce gas - controlled by a device that times a motor valve on pressure and plunger-arrival sensors. It deloads liquid from a gas well, and SCADA tunes the cycle to maximize production without killing the well.
A plunger-lift cycle begins with the shut-in, or build-up, phase. The surface valve is closed and the well is shut in, and with no flow leaving, casing pressure builds as gas from the reservoir accumulates in the annulus. During this time the plunger falls down the tubing to the bottom, coming to rest below the liquid that has collected there. The point of the shut-in phase is to store enough pressure to lift the plunger and the liquid slug above it all the way to surface, so its length is set by how much pressure the well needs to build.
When enough pressure has accumulated, the controller opens the valve to start the flow, or lift, phase. The stored casing pressure now has somewhere to go, and it drives the plunger upward through the tubing. The plunger acts as a mechanical interface, a piston that keeps the gas below it from slipping up past the liquid, so it carries the whole liquid slug above it to surface as one column rather than letting the gas blow through. The plunger arriving at surface, sensed by an arrival sensor, marks the successful removal of that slug of liquid.
After the plunger arrives, the well enters the afterflow, or flow-after-arrival, phase, during which the valve stays open and the well simply produces gas. With the liquid cleared, the gas flows freely for a while and this is when most of the cycle's gas production is made. As gas flows, though, the well's velocity eventually drops and liquid begins to accumulate again at the bottom, so afterflow cannot continue indefinitely. When the well can no longer lift its own liquid, the controller closes the valve, the plunger falls, and the next shut-in begins - completing the cycle.
The device that runs all of this is the plunger controller, which operates a surface motor valve - opening it to begin flow and closing it to shut the well in. It decides when to switch phases using a small set of inputs: casing and tubing pressure, and the plunger-arrival sensor that detects the plunger reaching the surface lubricator. From those it manages the timing - how long to build, how long to allow afterflow, when to shut back in - either on pressure setpoints, on timers, or on a combination of both. The controller is the brain that turns the physics of the cycle into an automated routine.
Plunger arrival is a particularly important input because it tells the controller whether the cycle worked. A plunger that arrives promptly confirms a good lift; a plunger that arrives late or not at all means the well did not have enough energy to lift the slug, and the controller must respond - typically by shutting in longer to build more pressure before the next attempt. Using arrival timing as feedback is what lets the controller adapt the cycle to the well rather than blindly running a fixed schedule that may be lifting too soon or too late.
Whether plunger lift works at all depends on the well having enough gas relative to the liquid it makes - the gas-liquid ratio, or GLR. The gas is the energy source that lifts the plunger and slug, so a well needs a minimum GLR for the reservoir's own pressure to do the lifting; below that, there simply is not enough gas per barrel of liquid to sweep the well, and plunger lift cannot sustain itself without supplemental gas. This is why plunger lift suits gas wells and gassy oil wells loading up with liquid, and why declining GLR is one of the things that eventually pushes a well past what plunger lift alone can do.
Plunger lift is a balancing act, and it is a balance SCADA is well placed to help hold. Shut the well in too long and you build more pressure than the lift needs, giving up gas production to unnecessary downtime. Open it too soon and the plunger arrives late or falls back, wasting a cycle and risking a dropped plunger. Run afterflow too long and liquid reloads faster than the next lift can clear, eventually loading the well up until it can no longer unload itself - the failure plunger lift is meant to prevent. The optimum threads between these, and it moves as the well declines.
A cloud SCADA platform such as Merobix supports finding that optimum by trending the cycle's signals - casing and tubing pressure sawtoothing through each phase, plunger-arrival times, and gas and liquid production per cycle - and by making them visible across many wells at once. Seeing arrival times drift late, or afterflow periods that end with the well loading up, tells an engineer the cycle timing needs adjusting, and the adjustment can be made and its effect watched remotely. Because plunger wells are typically numerous and spread out, that remote, per-well visibility is what makes systematic cycle tuning practical.
The most valuable SCADA function on a plunger well is catching a cycle that has gone wrong before the well loads up and dies. Alarming on a missed plunger arrival, on arrivals trending steadily later, or on production falling off signals a well whose energy is slipping below what the current timing assumes - a warning to lengthen the shut-in or shorten afterflow before the well can no longer clear its liquid. Deloading a gas well without killing it is precisely the line plunger lift walks, and continuous monitoring of arrivals and pressures is how that line is held across a whole field of wells.
A plunger lift cycle runs through shut-in, flow, and afterflow. During shut-in the valve is closed, pressure builds, and the plunger falls to the bottom below the accumulated liquid. During flow the valve opens and the stored pressure drives the plunger and its liquid slug to surface, and during afterflow the well produces gas freely until liquid begins loading up again, at which point the valve closes and the next cycle begins.
The controller operates a surface motor valve using casing and tubing pressure and a plunger-arrival sensor as inputs. It shuts the well in to build pressure, opens it to lift the plunger, and closes it after afterflow when the well can no longer clear liquid, timing those transitions on pressure setpoints, timers, or both. Plunger-arrival timing is key feedback - a late or missing arrival tells the controller to build more pressure next cycle.
Plunger lift relies on the well's own gas to lift the plunger and liquid slug, so the well needs enough gas relative to the liquid it produces - a sufficient gas-liquid ratio, or GLR. Below a minimum GLR there is not enough gas energy per barrel of liquid for the reservoir pressure to sweep the well, and plunger lift cannot sustain itself without supplemental gas. Declining GLR is one reason a well eventually outgrows plunger lift alone.
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