The Sucker Rod Pump: Components, How It Works and Why It Fails

What is a sucker rod pump?

A sucker rod pump is an artificial-lift system that uses a surface power source to drive a pump at the bottom of the well through a string of steel rods. It is also called a beam pump or rod pump. ¹³

Artificial lift is any system that adds energy to the fluid column in a wellbore to start or improve production. ² Rod pumping is one of the methods, alongside gas lift and electric submersible pumps. ² In the glossary's words, a beam and crank assembly creates reciprocating motion in a sucker-rod string, and the pump's plunger and valve assembly "convert the reciprocating motion to vertical fluid movement." ¹³

You'll find rod pumps on mature fields everywhere: Permian and Midcontinent strippers, Bakken horizontals, heavy oil in Alberta and California, and older fields from Argentina to Oman, Romania and Indonesia.

The surface unit: turning rotation into a stroke

The surface unit turns the rotation of a motor into the slow up-and-down stroke of the polished rod. The prime mover drives a gearbox, the gearbox turns the cranks, and the cranks rock the walking beam, whose horsehead lifts and lowers the rod string.

From the motor to the well, the main parts are:

1. Prime mover. An electric motor or gas engine.
2. Gearbox. Reduces motor speed to the few strokes per minute a rod string can take.
3. Cranks and counterweights. The beam and crank assembly creates the reciprocating motion; ³ the counterweights balance the weight of the rods and fluid so the gearbox isn't lifting all of it on every upstroke.
4. Walking beam and horsehead. The beam rocks on the samson post; the curved horsehead at its end keeps the rods hanging straight over the well.
5. Bridle, carrier bar and polished rod. The bridle hangs from the horsehead and the carrier bar clamps the polished rod, the uppermost joint of the rod string. The polished rod's smooth surface lets a seal be made around the moving rods at the wellhead. ⁴

The surface unit is also where most measurements are taken: a load cell on the polished rod and a position sensor give the dynamometer card. See the dynamometer card guide.

The rod string: the link to the pump

The rod string is a column of steel sucker rods, each 25 to 30 ft long and threaded at both ends, coupled together from the polished rod down to the pump. It carries the pump's load up on every upstroke. ⁵

The rods are the part of the system most likely to fail, because they carry a load that changes on every stroke for years. Three things decide how long they last:

• String design. Rod sizes, a taper from heavier rods at the top to lighter at the bottom, and often sinker bars at the bottom to keep the lower string in tension.
• Connections. Every coupling has to be made up to the right pin prestress, or it loosens and the pin breaks. See why sucker rods part.
• What the downstroke does to the bottom of the string. Compression there causes buckling and wear against the tubing.

The downhole pump: barrel, plunger and two valves

The downhole pump is a barrel with a plunger moving inside it and two check valves: the standing valve at the bottom of the barrel and the traveling valve in the plunger. Together they let fluid into the barrel on the upstroke and lift it up the tubing. ⁶⁷

• Barrel. The cylinder the plunger moves in. It sits at the bottom of the tubing, below the fluid level.
• Plunger. A close-fitting piston on the end of the rod string.
• Standing valve. A check valve at the bottom of the barrel that lets fluid flow up to fill the barrel and stops it from flowing back down. ⁶
• Traveling valve. A check valve in the plunger that closes the barrel chamber so the trapped fluid can be lifted. ⁷

There are two common layouts. In an insert pump, the whole pump runs in and out on the rods and seats in the tubing. In a tubing pump, the barrel is part of the tubing string and only the plunger comes out with the rods. Many wells also run a tubing anchor to stop the tubing from stretching and moving with every stroke.

How the pumping cycle works

Each stroke has two halves. On the upstroke the traveling valve closes and the plunger lifts fluid while the standing valve opens to refill the barrel. On the downstroke the standing valve closes and the traveling valve opens so the plunger can move down through the fluid it just drew in. ⁶⁷

1. Upstroke. The traveling valve closes. The plunger lifts the column of fluid above it toward the surface, and the rods carry that fluid load. Below the plunger, pressure drops, the standing valve opens, and fluid from the well fills the barrel. ⁶⁷
2. Top of stroke. The plunger stops and reverses. The standing valve closes.
3. Downstroke. The traveling valve opens and the plunger moves down through the fluid in the barrel. The fluid load moves off the rods and onto the tubing.
4. Bottom of stroke. The plunger reverses and the cycle repeats.

A healthy pump fills completely on every upstroke. When it doesn't, because the well can't supply fluid fast enough or gas gets into the barrel, the cycle goes wrong in ways the dynamometer card shows clearly. ⁸

Why sucker rod pumps fail

Most rod-pump failures come from a few root causes: compression and buckling at the bottom of the string, fluid pound on pumped-off wells, gas in the pump, corrosion and fatigue in the rods, and loose connections. Each has its own symptoms and its own fix.

The cost of each failure is a pulling job plus the production lost while the well waits for a rig. See workover cost and stripper well economics.

Where SRABS fits

SRABS changes two parts of this picture: the downhole pump, and how the well is controlled.

The SRABS Pump is "a mechanically re-engineered sucker rod pump that keeps the rod string in tension where it would otherwise buckle." It's a drop-in to API spec. 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, and checks them against the physics of your rod string." See the system and how it works.

To estimate what fewer failures would mean for your fleet, run the ROI calculator. Its default 100-well scenario is modelled, not a field result.

The bottom line

A sucker rod pump is three systems working as one: a surface unit, a rod string and a downhole pump. Most failures start where they meet: at the bottom of the string, in the barrel and at the connections. Learn to read the card and the fluid level, and the pump will tell you which one is the problem.

If the same wells keep failing, test the fix on one well.

FAQ

Sources

1. SLB Energy Glossary, "sucker-rod pump." https://glossary.slb.com/en/terms/s/sucker_rod_pump
2. SLB Energy Glossary, "artificial lift." https://glossary.slb.com/en/terms/a/artificial_lift
3. SLB Energy Glossary, "beam pump." https://glossary.slb.com/en/terms/b/beam_pump
4. SLB Energy Glossary, "polished rod." https://glossary.slb.com/en/terms/p/polished_rod
5. SLB Energy Glossary, "sucker rod." https://glossary.slb.com/en/terms/s/sucker_rod
6. SLB Energy Glossary, "standing valve." https://glossary.slb.com/en/terms/s/standing_valve
7. SLB Energy Glossary, "traveling valve." https://glossary.slb.com/en/terms/t/traveling_valve
8. Gibbs, S. G., US Patent 3,343,409, "Method of determining sucker rod pump performance" (Shell Oil Co., 1967). https://patents.google.com/patent/US3343409