Electric submersible pump
Due to the reduction of the driving force which lifts the reservoir from downhole naturally, pumps were commonly used to increase the back pressure
for production, which is a form of artificial lift. The electric submersible pump (ESP) is an effective and economical method of lifting large volume of the fluids from downhole under different well conditions. ESP system requires a large electricity supply, but it is less complex and more efficient than delivering gas to gas lift systems.
ESP Components
An ESP system may include following components:
• Three phase electric motor;
• Seal assembly;
• Rotary gas separator;
• Multi-stage centrifugal pump;
• Electrical power cable;
• Motor controller;
• Transformers.
Applications
Different from the surface pump system, the ESP systems are particularly designed to be immersed in fluid. It can be either located in a well or on the seabed. The ESP motors are pressure balanced with the environment, whether that is downhole pressure or water pressure in subsea conditions.
Optional components of the ESP system may include tubing joints, check valve, drain valve, downhole pressure and temperature transmitters, etc. Figure shows a typical ESP configuration in downhole. The selection of ESP types mainly depends on the well fluid properties.
Following are the three major types of ESP applications:
• High water-cut wells producing fresh water or brine;
• Multi-phase flow well with high GOR;
• Highly viscous fluid Well.
Pump rate
The pump rate is a function of the rotational speed, the number of stages, the dynamic head acting against the ESP and the pumped fluid viscosity.
These factors dictate the differential pressure across a pump system, and therefore the flow rate. However, for a given pump, there is an optimal
design flow rate that maximizes pump efficiency and run life. Figure shows the operating range recommended by ESP manufacturers.
Sizing of ESP is based on predicted completion performance, or flow rate. This usually involves examination of the well inflow performance
relationship (IPR), which describes the production response to changes in bottomhole pressure (BHP).
How to size ESP
Data required for calculation and sizing of ESP includes well data, production data, well fluid conditions, power sources and possible problems
etc. Calculations for designing an ESP system include:
• Determination of Pump Intake Pressure;
• Calculation of total dynamic head ;
• Selection of pump type;
• Check of load limits;
• Selection of accessory and optional equipment.
Operational challenges
- Scale deposit can form on the pump motor due to high surface temperature. This can lead to over heating of the motor and cause failure.
