Gas-Locked Rod Pump: How to Diagnose and Fix Gas Lock
What is gas lock in a rod pump?
Gas lock is when a rod pump's barrel holds so much gas that the plunger can't raise the pressure enough to open the traveling valve on the downstroke. The gas only compresses and expands, the valves stay shut, and the pump strokes without lifting any fluid. 12
A sucker rod pump is built to move liquid. On the upstroke, the standing valve at the bottom of the barrel opens and fluid flows in. On the downstroke, the plunger moves down, the pressure under it rises, and the traveling valve in the plunger opens once that pressure exceeds the hydrostatic load of the fluid column in the tubing above it.
Gas changes that sequence. Gas compresses where liquid doesn't, so a barrel holding a lot of free gas spends much of the downstroke just compressing it. If there's enough gas, the pressure never reaches the point that opens the traveling valve. The patent literature describes it this way: too much gas in the compression chamber can completely eliminate the pump's ability to lift fluid, because the gas can't be compressed to a pressure high enough to overcome the hydrostatic pressure on the traveling valve. 1
The well looks like it's running: the unit turns and the rods move. But nothing reaches the surface.
Gas lock vs. gas interference vs. fluid pound
Gas interference, gas lock and fluid pound all show up as an incomplete pump card, but they have different causes and different fixes. Gas interference reduces how much the pump lifts, gas lock stops it lifting altogether, and fluid pound is a pumped-off well hitting liquid. 123
| Gas interference | Gas lock | Fluid pound | |
|---|---|---|---|
| What happens | Free gas takes up part of the barrel; pump efficiency drops | So much gas that the traveling valve never opens; no fluid lifted | Barrel only partly filled because the well is pumped off; plunger hits liquid |
| Cause | Gas entering the pump intake with the liquid | Severe gas interference 12 | Pump displacement greater than inflow 3 |
| Fluid level | Often well above the pump | Often well above the pump | Close to the pump intake |
| Card shape | Rounded, gradual load release on the downstroke | Little or no load change: an almost flat, narrow card | Full load held into the downstroke, then a sharp drop |
| First fix | Separate the gas before it reaches the pump | Get the gas out of the barrel, then separate it | Match pump rate to inflow |
The patents describe gas lock as a type of gas interference: the same problem taken to the point where pumping stops. 12 In practice a well can move between the two as gas rates change from day to day.
The fluid-level column is the quickest way to tell gas problems from pump-off. A gas-interfered well can have plenty of fluid over the pump and still fill the barrel poorly. A pounding well has run out of fluid. See the fluid pound guide for that side of the comparison.
- G1 Gas interference
The bottom-right corner rounds off: gas compresses until the traveling valve opens.
- G2 Gas lock
So much gas the traveling valve never opens: the card collapses into a thin loop.
- G3 Fluid pound
Full load held into the downstroke, then a sharp drop where the plunger hits liquid.
Why rod pumps gas-lock
Gas lock comes from free gas reaching the pump intake faster than the pump can handle it. The risk grows with gassy fluid, a pump set above the producing zone, large chambers that hold more gas, and gas collecting around the seating nipple. 245
- Free gas at the intake. As fluid flows toward the pump and pressure drops, dissolved gas comes out of solution. Gas that isn't separated in the annulus gets drawn into the barrel with the liquid.
- Pump setting relative to the perforations. When the pump sits above where fluid enters the wellbore, gas and liquid arrive at the intake together and the pump has to separate them itself. A gas anchor is usually connected to the pump's suction inlet for exactly this reason. 4
- Large-bore pumps. One patent notes the problem gets worse in large-bore pumps, where the larger chamber gives gas more room to collect. 2
- Gas collecting at the seating nipple. Another patent describes free gas building up below the pump intake, within and below the seating nipple, and says conventional seating nipples have been known to let gas collect there. 5
Whether the well is a Permian horizontal, a Bakken producer, or a mature well in Argentina or Kazakhstan, the physics in the barrel is the same: free gas at the intake takes up room the liquid should have.
How to diagnose a gas-locked pump
Diagnose gas lock with the dynamometer card and a fluid-level reading together: a card showing the pump barely unloading, alongside a fluid level well above the intake and little or no production, means gas in the barrel, not an empty well. 36
- Read the card. A gas-locked pump card is narrow: the load hardly changes between upstroke and downstroke, because the traveling valve never opens and the plunger never picks up the fluid load. A gas-interfered card shows the downstroke load coming off gradually, as gas compresses, instead of all at once.
- Check the fluid level. A fluid-level survey gives pump submergence, the height of liquid over the intake. 6 High submergence with almost no production points to gas. Low submergence points to pump-off instead.
- Check production and casing pressure. A sudden drop to near zero on a well that was producing, with the unit still running normally, fits gas lock. Rising casing pressure means gas is building in the annulus.
- Rule out mechanical failure. A parted rod or a stuck-open or leaking valve can also stop production. The card helps here: a parted rod shows a sharp loss of load across the whole stroke.
How to fix a gas-locked pump
Short-term field fixes free a gas-locked pump but can damage it; the lasting fixes keep free gas out of the barrel. That means setting the pump below the perforations where possible, adding a gas anchor or separator, choosing pump hardware that handles gas, and controlling the well so it doesn't draw gas in. 124
Field fixes, and what they cost
The common field practice is to space the pump so it taps bottom on the downstroke, jarring the traveling valve open. 12 It works, but both patents warn that hitting the pump to open the valves damages pump components and the rod string. 12 Treat tagging as a temporary measure, not a way to operate the well.
Keep the gas out of the pump
- Set the intake below the perforations if the well allows it. Liquid then flows down past the zone to reach the pump while gas rises up the annulus. This is the natural separation that gas-separator design tries to reproduce.
- Gas anchors and downhole separators. A gas anchor connected to the pump inlet gives gas time to separate. It works because bubbles rise through oil or water at roughly six inches per second, so gas separates wherever the downward liquid velocity stays below that rise rate. 4 The same patent says plainly that no gas anchor is totally effective, because dissolved gas can still come out of solution with changes in temperature, pressure or agitation. 4
- Vent gas away from the seating nipple. Some seating-nipple designs vent gas that collects around the pump intake into the casing. 5
- Gas-bleed hardware. Patent literature also describes bushings with a gas-bleed port that let trapped gas escape on the downstroke. 2
Control the well so it doesn't pull gas in
Gas problems get worse when a well is pumped hard: lower intake pressure lets more gas come out of solution right at the pump. Running the pump at a rate that matches inflow, and holding a steady submergence, reduces how much free gas reaches the barrel. That is a control problem, and it needs a current fluid-level reading.
This is where SRABS works on gas-locked wells. SRABS Echo is "an automated acoustic edge device" that reads fluid level, fully remote, and SRABS Brain "reads every dynamometer card, motor current and Echo fluid level." For gas-locked wells, the solutions page puts it in one line: "Echo sees the gas and the fluid level, and Brain adjusts speed and idle time before the pump starts to pound." See solutions, the system and the modelled gas-locked pump scenario.
Gas and fluid pound also add to downstroke compression at the bottom of the string. That ties gas handling to sucker rod buckling.
To estimate what fewer pulls would mean on your own fleet, run the ROI calculator. Its default 100-well scenario is modelled, not a field result.
The bottom line
A gas-locked pump is a well that still has fluid but can't lift it. Tagging the pump gets it going again at a cost. Setting the intake below the perforations, gas separation and gas-handling hardware reduce how much gas reaches the barrel. Steady, inflow-matched control keeps the intake pressure from releasing more gas in the first place.
If you have wells that keep losing production with the unit still running, read the cards against a fluid-level reading, then test closed-loop control on one well.
FAQ
What does it mean when a rod pump is gas-locked?
The barrel holds so much gas that the plunger can't build enough pressure to open the traveling valve. The gas compresses and expands on every stroke and no fluid is lifted, even though the unit keeps running.
What is the difference between gas lock and gas interference?
Gas interference means gas takes up part of the barrel and reduces how much the pump lifts. Gas lock is the severe case, where the traveling valve stops opening and the pump lifts nothing.
How do you fix a gas-locked pump?
In the field, operators often tap the pump on bottom to jar the valve open, but that damages the pump and rods. The lasting fix is to keep gas out: set the intake below the perforations if possible, use a gas anchor or separator, and run the well at a rate that holds steady submergence.
How do you tell gas lock from fluid pound?
Check the fluid level. Gas lock and gas interference usually have fluid well above the pump. Fluid pound happens when the well is pumped off and the fluid level is down at the intake.
Does a gas anchor stop gas lock?
It reduces it. A gas anchor gives gas time to separate before it enters the pump, but no gas anchor is fully effective, because gas can still come out of solution at the intake.
Why does tagging the pump fix gas lock?
Spacing the pump to tap bottom jars the traveling valve open and lets the trapped gas out. It's a short-term fix: hitting the pump repeatedly damages pump parts and the rod string.
Sources
- US Patent 7,458,787, "Apparatus and method for reducing gas lock in downhole pumps" (Harbison-Fischer). https://patents.google.com/patent/US7458787
- US Patent 10,316,838, "Method and apparatus for preventing gas lock/gas interference in a reciprocating downhole pump" (Downing Innovations, 2019). https://patents.google.com/patent/US10316838
- SLB Energy Glossary, "fluid pound." https://glossary.slb.com/en/terms/f/fluid_pound
- US Patent 9,022,106, "Downhole diverter gas separator" (J. N. McCoy, 2015). https://patents.google.com/patent/US9022106
- US Patent 11,028,683, "Downhole pump gas eliminating seating nipple system" (Stoneview Solutions, 2021). https://patents.google.com/patent/US11028683
- Acoustic Fluid Level Measurements, Chapter 8, "Applications of Fluid Level Measurements to Pumping Wells," Petroleum Extension Service (PETEX). https://utw10286.utweb.utexas.edu/images/flippingbooks/acoustic_fluid_measure/files/basic-html/page15.html