SPE Artificial Lift Systems 3 — Questions and Answers
Question 1: In sucker rod lift design, the 'API unit designation' 640D-365-144 indicates which parameter with value 640?
- Maximum polished rod load in hundreds of pounds
- Peak torque rating in thousands of inch-pounds (Correct answer)
- Stroke length in inches
- Pump depth in feet
Correct answer: Peak torque rating in thousands of inch-pounds
In the API pumping unit designation, the first number (640) is the peak torque rating in thousands of inch-pounds, D indicates the geometry type.
Question 2: Which phenomenon causes ESP gas locking, and what is the standard mitigation?
- Scale buildup blocking impellers; resolved by chemical injection
- Free gas accumulating in the pump, stopping liquid flow; mitigated by a gas separator or shroud (Correct answer)
- High viscosity fluid stalling the motor; resolved by heating the wellbore
- Emulsion formation in impellers; resolved by increasing pump speed
Correct answer: Free gas accumulating in the pump, stopping liquid flow; mitigated by a gas separator or shroud
Gas locking occurs when free gas fills pump stages and prevents liquid from flowing; a rotary gas separator or shroud-and-perforated-pipe assembly routes free gas away from the pump intake.
Question 3: What is the 'GLR test' used for when designing a plunger lift installation?
- Measuring gas injection rate required for continuous gas lift
- Determining if there is sufficient energy in produced gas to lift a plunger slug to surface (Correct answer)
- Calculating gas-liquid ratio in ESP pump stages
- Evaluating separator efficiency at the surface facility
Correct answer: Determining if there is sufficient energy in produced gas to lift a plunger slug to surface
The GLR test compares the well's producing GLR against the minimum GLR needed to lift a plunger, confirming whether plunger lift is energetically feasible.
Question 4: In hydraulic jet pump systems, what role does the 'power fluid' play?
- It lubricates the jet nozzle and diffuser
- It is injected at high pressure through a nozzle to entrain and lift formation fluid via the Venturi effect (Correct answer)
- It cools the downhole pump motor
- It provides hydraulic force to open and close downhole safety valves
Correct answer: It is injected at high pressure through a nozzle to entrain and lift formation fluid via the Venturi effect
Power fluid is injected at high velocity through a jet nozzle, creating a low-pressure zone that entrains formation fluid, and both fluids are lifted to surface through the diffuser and return tubing.
Question 5: For sucker rod strings, what is the purpose of using tapered rod designs (mixing rod sizes)?
- To reduce polished rod load by minimizing rod string weight
- To optimize stress distribution along the rod string and maximize allowable pump depth (Correct answer)
- To increase stroking speed without exceeding API torque limits
- To reduce tubing wear by keeping rods centered
Correct answer: To optimize stress distribution along the rod string and maximize allowable pump depth
Tapered rod strings use larger-diameter rods near the surface (higher stress) and smaller-diameter rods near the pump to equalize stress distribution and maximize operating depth.
Question 6: Which artificial lift system is best characterized by having no downhole moving parts and using injected gas bubbles to reduce fluid density?
- Sucker rod pump
- Hydraulic piston pump
- Continuous gas lift (Correct answer)
- Electric submersible pump
Correct answer: Continuous gas lift
Continuous gas lift injects gas into the tubing to aerate the fluid column, reducing its density and allowing reservoir pressure to push the lighter mixture to surface — with no downhole moving parts.
Question 7: What is the primary cause of 'gas interference' in a sucker rod pump, and how is it diagnosed on a dynamometer card?
- Sand eroding the barrel; diagnosed by gradual load increase on upstroke
- Free gas compressing in the barrel instead of lifting fluid; shows as a rounded load transfer on the downstroke with reduced fluid load (Correct answer)
- Rod part causing sudden load drop; appears as a vertical line drop on the card
- Tubing leak causing excess fluid recycling; shows a shifted card baseline
Correct answer: Free gas compressing in the barrel instead of lifting fluid; shows as a rounded load transfer on the downstroke with reduced fluid load
Gas interference compresses in the pump barrel during the downstroke before the traveling valve opens, producing a characteristic rounded 'pinched' dynamometer card shape with reduced effective fluid load.
SPE Artificial Lift Systems 3
In sucker rod lift design, the 'API unit designation' 640D-365-144 indicates which parameter with value 640?