Tag Archives: production technologist

ESP: Gas handling device

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Gas  handling  devices  may  be  a  better  alternative  for  wells  prone  to  high  free  gas, slugging, foams and emulsions. These are essentially centrifugal pumps with large stages, mixed  (or  axial)  impellers,  large  vane  openings,  steep  vane  exit  angles  and  sometimes include multiple  vanes. 

Instead of separating, their purpose is to break large gas bubble into smaller ones thereby reducing the risk of gas locking and making it easier for gas to be re-absorbed into solution, and to homogenize the gas with liquid phases, prior to entering the pump intake.

An additional benefit of gas handlers is, because more gas is retained in the flow stream, this gas is then available to help lift fluids in the tubing above the ESP discharge head thereby reducing hydraulic horsepower requirements.

Applications: A Gas Handler is generally considered if the Free Gas Percentage at the intake of the pump is from 30% to 60% by volume.

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ESP: Pump Intake

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As the name suggests “ Pump Intake ” is where the well fluid enters the Submersible Pumping System. Care should be taken when designing a submersible pump intake because it is such a vital point in the system that when not designed properly may create all kinds of problems.

There are three types of intake Sections:

  • Standard Intakes or BOI (bolt on intake),
  • Integral (manufactured as part of the pump),
  • Gas Separators (static and rotary gas separators).

Standard and Integral Intakes:

Standard intakes (BOI and integral) do not separate gas.  Some gas separation might occur, but it will only be natural separation due to some of the gas not turning and going into the intake when the rest of the fluid does. Therefore, the standard intake is for wells that produce with a very low free gas to liquid ratio. The amount of free gas by volume at pump intake conditions should be no more than 10% to 15% by volume (depends if it is a radial or mixed flow stage)
                           

Usually, the pump intake is a separate component that bolts onto the bottom of the pump section. Occasionally, the pump is built in either a lower tandem or single configuration. In these cases, the pump intake as an integral part of the pump assembly.

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Compression Pump vs. Floater Pump

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There are mainly two designs of electrical submersible pump stages widely used by ESP’s service companies: 

  • Fixed impeller or compression pump design: every impeller is fixed to the shaft and is not free to move up and down. Hence, it cannot move without the shaft moving. All the impellers are “compressed” together to make one rigid body.
  • Floating stage design: each impeller in a floater pump is free to move up and down on the shaft within the confines of the diffuser as depicted in the following Figure. The thrust washers on the impeller support the stage thrust. The amount of thrust varies with liquid rate (the amount of fluid being pumped).

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ESP: Pump Stage

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A “ Pump Stage ” consists of an impeller, diffuser and thrust washers. As shown by the following figure, the impellers rotate with the shaft and spin at the RPM of the motor. The stationary diffusers turn the fluid into the next impeller and do not rotate. Pumps are assembled by stacking stages on a shaft and compressing the stack in a housing. A stage will produce a given amount of flow and lift (head) at the motor RPM.

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Pump impeller types

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The pump stages are of a fully enclosed curved vane design, whose maximum efficiency is a function of impeller types and designs. There are two basic types of stages used in oil well submersible pumps: stages with Mixed flow impeller and stages with Radial flow impeller.

 

The difference between these two types of designs is described by the pump impeller vane angles and the size and shape of the internal flow passages, as depicted in the graphs below.

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