SPE - Society of Petroleum Engineers Artificial Lift Systems Questions and Answers 1 — Questions and Answers
Question 1: An engineer is selecting an artificial lift system for an offshore well characterized by a high production rate (>10,000 BPD), moderate depth, and a low gas-oil ratio (GOR). The wellbore is deviated. Which artificial lift system is most suitable for these conditions?
- Sucker Rod Pump
- Gas Lift
- Electrical Submersible Pump (ESP) (Correct answer)
- Plunger Lift
Correct answer: Electrical Submersible Pump (ESP)
Electrical Submersible Pumps (ESPs) are specifically designed for high-volume applications and are commonly used offshore due to their compact surface footprint and ability to generate the high horsepower required for large flow rates. Sucker rod pumps are generally unsuitable for deviated wells and have lower volume capabilities. Gas lift is more efficient in wells with higher GOR. Plunger lift is a low-volume system for high-GOR wells.
Question 2: In a continuous-flow gas lift design, what is the primary function of the deepest valve, also known as the operating valve?
- To automatically open and close to create an intermittent flow regime.
- To provide the primary and deepest point for continuous gas injection into the production tubing. (Correct answer)
- To unload the well of completion fluids during the initial startup phase.
- To act as a safety valve to prevent casing over-pressurization.
Correct answer: To provide the primary and deepest point for continuous gas injection into the production tubing.
In a continuous gas lift system, shallower 'unloading' valves are used to start the well by displacing heavy fluids. However, once the well is operational, the operating valve, which is the deepest valve, serves as the primary and most efficient point for continuous gas injection to lighten the fluid column and sustain production.
Question 3: Which of the following conditions represents a significant operational limitation for Progressing Cavity Pumps (PCPs) due to the material properties of their standard components?
- High fluid viscosity.
- High gas-oil ratio (GOR).
- Presence of abrasive solids.
- High bottom-hole temperature. (Correct answer)
Correct answer: High bottom-hole temperature.
Standard Progressing Cavity Pumps use a stator made of a synthetic elastomer. High bottom-hole temperatures (typically >250-300°F) can cause this elastomer to swell, degrade, or otherwise fail, leading to rapid pump failure. While PCPs are an excellent choice for viscous and abrasive fluids, temperature is a critical material limitation.
Question 4: An operator analyzes a downhole dynamometer card from a sucker rod pump and observes a sharp drop on the downstroke that occurs before the plunger reaches the bottom of its stroke, followed by a sharp impact line. What is the most likely cause of this 'fluid pound' signature?
- The pump's displacement capacity is greater than the well's inflow, causing incomplete pump fillage. (Correct answer)
- The tubing anchor has failed, allowing the tubing to move with the rod string.
- The traveling valve is leaking, allowing fluid to slip past during the upstroke.
- The standing valve is completely plugged with scale or debris.
Correct answer: The pump's displacement capacity is greater than the well's inflow, causing incomplete pump fillage.
Fluid pound occurs when the pump barrel is not completely filled with liquid on the upstroke. On the subsequent downstroke, the plunger falls freely through the gas-filled void until it impacts the top of the liquid column, causing a damaging shock load. This condition is a classic sign that the pump is trying to lift more fluid than the reservoir can provide, also known as being 'pumped off'.
Question 5: Plunger lift is an artificial lift method that is most effective and economically advantageous under which specific set of reservoir and well conditions?
- Low bottom-hole pressure, low productivity index, and high water cut.
- High bottom-hole pressure, high productivity index, and low gas-liquid ratio.
- High gas-liquid ratio, sufficient bottom-hole pressure to lift the plunger, and a tendency for liquid loading. (Correct answer)
- Deep wells with highly viscous crude oil and significant sand production.
Correct answer: High gas-liquid ratio, sufficient bottom-hole pressure to lift the plunger, and a tendency for liquid loading.
Plunger lift harnesses the energy from a well's own produced gas. It is most effective in wells with a high gas-liquid ratio (GLR) that can build up enough casing pressure during a shut-in period to lift the plunger and the accumulated liquid slug to the surface. It is specifically applied to mitigate liquid loading in gas wells or produce high-GOR oil wells.
Question 6: An engineer is selecting an artificial lift system for a mature, onshore vertical well at a depth of 7,000 ft. The well produces a low volume of non-gassy fluid (<200 BPD) and has readily available electrical power. The operator prioritizes operational simplicity, durability, and extensive industry familiarity. Which system is the most conventional and appropriate choice?
- Gas Lift
- Sucker Rod Pump (Correct answer)
- Progressing Cavity Pump (PCP)
- Electrical Submersible Pump (ESP)
Correct answer: Sucker Rod Pump
The sucker rod pump (or beam pump) is the most widely used artificial lift system globally, especially for the described conditions: onshore, moderate-depth vertical wells with low to medium production rates. It is renowned for its robustness, straightforward operation, and the vast amount of industry experience available for its design, operation, and troubleshooting, aligning with the operator's priorities.
SPE - Society of Petroleum Engineers Artificial Lift Systems Questions and Answers 1
An engineer is selecting an artificial lift system for an offshore well characterized by a high production rate (>10,000 BPD), moderate depth, and a low gas-oil ratio (GOR).
The wellbore is deviated.
Which artificial lift system is most suitable for these conditions?