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Electrical Submersible Pump Systems (ESP)

Jul 29, 2024

Electric Submersible Pumping (ESP) Systems Lecture

Introduction to ESP

  • What is ESP?: A type of mechanical assist artificial lift system using a multistage centrifugal pump to produce formation fluids (water, oil, oil with gas).
  • Main Categories of Artificial Lift: Formation pressure assist and mechanical assist.
  • ESP in the Context of Artificial Lift:
    • Sub-categories of mechanical assist: positive displacement and dynamic displacement.
    • ESP falls under dynamic displacement.
  • Usage: Second most used artificial lift system globally, but first in volume of production.
    • Suitable for high volume wells (15,000+ feet depths, >60,000 barrels/day).
    • Not for high temperature unless special cooling techniques are used.
    • Can handle gas with specific pump configurations and gas separators.
    • Challenges in solids and high viscous fluid production.
    • Workover rigs required for well interventions.
    • Surface components have moderate efficiency (35-60%).

Advantages of ESP

  • High volume production suitability.
  • Can be used in slimhole and deviated wells.
  • Appreciable total system efficiency compared to the power used.
  • Minor surface equipment impact.

Limitations of ESP

  • Requires high power and voltage at the surface.
  • Potential issues with the power cable during installation.
  • Temperature management is critical to motor performance.
  • Difficulty in field repairs, usually done offsite.
  • Costly and time-consuming to pull and reinstall.

Equipment Components

Downhole Components

  • Electric Motor: A three-phase motor that drives the pump.
  • Seal Section/Protectors: Prevents formation fluid from entering the motor, absorbs motor oil expansion, equalizes pressure, and transfers torque.
  • Pump Intake: Allows fluid entrance into the pump; can also function as a gas separator.
  • Centrifugal Pump: Multistage, dynamic displacement pump that provides lift through centrifugal force.
  • Electric Cable: Transports power from surface to downhole motor.
  • Optional Components: Sensors, packers, check valves.
  • Variable Speed Drives: Allow for speed adjustments to match well productivity.

Surface Components

  • Wellhead: Special tubing head with connection for power cable.
  • Junction Box: Used for safe venting of gas, electric measurements, and simplicity.
  • Transformers: Either step-up or step-down to manage voltage supplied to the motor.
  • Motor Controllers: Fixed speed switchboard, soft starter, or variable speed drive.
  • Surface Cables: Connect switchboard, Transformer, and junction box to wellhead.

Design and Selection

ESP Performance Curve

  • Relationship between head against flow rates for a centrifugal pump.
  • Constant Head: A property of centrifugal pumps regardless of fluid being pumped.

e.g. In a well needing 15,000 feet of lift for a flow rate of 600 barrels/day with each pump stage lifting 40 feet:

  • Number of stages required = Total lift / Lift per stage = 15,000 / 40 = 375 stages.

Operating Conditions

  • Balanced Operation: Ensure no down-thrust (impeller pushed down), or up-thrust (impeller pushed up).
  • Optimal Operating Range: Specified range ensuring no mechanical contacts causing erosion or efficiency issues.

Calculations for Total Dynamic Head (TDH)

  • Components of TDH: Net vertical lift, friction loss, wellhead pressure.
  • Example: To produce 3600 barrels/day with TDH of 4590 feet using a stage lifting 45 feet, requires 102 stages minimum.

Selecting the Pump & Motor

  • Key Factors:
    • Desired production rate and bottom hole flowing pressure.
    • Net positive suction head (NPSH) and stages required.
    • Horsepower required to drive the pump and bottom hole assembly.
    • Cable size and voltage drop management.

Practical Calculations

  • Determine Performance Curve: Use performance data against desired flow rate.
  • Head Per Stage: Example given 45 ft needed for 4,590 ft lift = 102 stages.
  • Calculate Horsepower Required: Based on pump's performance and desired well operation.

Summary

  • ESP systems are a critical high-volume artificial lift method with specific design and operational considerations.
  • Performance and efficiency are balanced against operational challenges and limitations. Efficiently managing these systems extends their life and operational reliability.

Final Remarks and Further Reading

  • For detailed steps on ESP design, refer to resources on nine-step ESP design methodologies.

Questions and Answers

  • Open floor for attendee inquiries on ESP systems and related artificial lift technologies.

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