A sucker rod pump is a simple machine that fails for unglamorous reasons: a barrel worn oval, a ball that no longer seats, a plunger that was specified for the wrong fluid. The pump at the bottom of the string has no instrumentation and no second chance, so the selection has to be right before it goes in the hole. Barrel material, plunger finish and valve trim are the three decisions that decide how long the pump lasts. On the rig, the pump is the last item run and the first item blamed, so the selection file should travel with the job.
How a Sucker Rod Pump Lifts Fluid
The pump has four working parts: barrel, plunger, standing valve and traveling valve. On the upstroke the traveling valve closes and the plunger lifts a column of fluid while the standing valve opens and lets new fluid into the barrel. On the downstroke the standing valve closes and the traveling valve opens, so the fluid passes through the plunger and the cycle repeats. Every stroke moves a fixed volume, which is why the pump constant matters more than the pump length. The crew reads the stroke count and the fluid level, and those two numbers are only meaningful against a known displacement.
Barrel and Plunger Surface Options
The barrel can be carbon steel, chrome plated, nickel-phosphorous plated, carbonitrided or carburized, and a brass barrel is available for specific duties. The plunger can be carbon steel, nickel sprayed or chrome plated, with a double chrome option for abrasive service. The pairing is what matters: a hard barrel with a soft plunger wears the plunger, and two hard surfaces in a sandy well can gall. The workover report usually says which part failed, and that is the information the next selection should use. In the field, the same pump model run in two different wells can last two years or two months, and the difference is usually the sand and the fluid, not the pump.
Sizes and Pump Constant
Nominal diameters run from 32 mm (1.25 inches) to 95 mm (3.75 inches), with plunger lengths of 1.2 to 1.8 meters (4 to 6 feet) and stroke lengths from 0.6 to 7.3 meters. Pump constant rises with diameter, from 1.14 cubic meters per day on the 32 mm pump to 10.26 on the 95 mm pump, which is the number used to match the pump to the well's inflow. Tubing connections are 2-7/8 NU or EU on the smaller pumps and 3-1/2 or 4-1/2 NU or EU on the largest, with rod sizes from 3/4 to 1 inch. A pump that is one size large for the inflow will pump off and wear the barrel dry, which is a common failure in a well that was never tested after completion.
Valves, Balls and Seats
The standing and traveling valves are the parts that see the fluid at its dirtiest. Balls and seats are available in stainless steel, tungsten carbide and titanium carbide, with nickel carbide as an option. In a well with sand or scale, the carbide trim is the difference between a pump that holds its efficiency and one that starts slipping after a few weeks. The cage material and the hard lining follow the same logic. On a workover the valve is the first part the crew checks, because a ball that does not seat shows up as a pump that holds pressure on the downstroke and slips on the upstroke.
Match the barrel and plunger finish as a pair, not as two separate upgrades.
Choose carbide balls and seats where sand is produced.
Record the pump constant so the production test can be interpreted.
Sucker Rod Pump Checks on the Workover
On the workover, the pump is inspected rather than simply replaced. Look at the barrel for a wear ring at the plunger travel, check the standing valve for a cut seat, and confirm the plunger fit by hand before the pump goes back in. The rod string is checked at the same time, because a pump that fails early is often a symptom of a rod string that is loading it unevenly. At the wellsite, the pull is also the chance to check the tubing for wear opposite the rod couplings.
A sucker rod pump is a consumable with a predictable wear pattern. Read the pattern from the last pull, choose the barrel, plunger and trim for the fluid, and the next run lasts longer than the last one.
For more information, please contact China Vigor at info@vigorpetroleum.com or call +0086 29 81161513.
