Electrical generator or motor structure – Dynamoelectric – Rotary
Reexamination Certificate
1999-11-17
2001-03-13
Mullins, Burton (Department: 2834)
Electrical generator or motor structure
Dynamoelectric
Rotary
C417S421000, C417S423900
Reexamination Certificate
active
06201327
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates generally to downhole pumping systems, and more particularly to a motor protector for use with a downhole pumping system.
BACKGROUND OF THE INVENTION
Electric submergible pumping systems are widely used throughout the world for moving subterranean fluids to a desired location, e.g. the earth's surface. These electric submergible pumping systems include an electric motor that is drivingly coupled to a pump. Generally, the electric motors used for such applications are rotary motors containing a rotor and a stator. Typically, the rotor lies within a fluid filled cavity within the stator. The fluid not only lubricates the motor, but also cools the motor to prevent overheating.
However, deleterious materials, such as carbon dioxide, hydrogen sulfide and brine, can be found in the subterranean fluids. Those substances can corrode, or otherwise harm components within the electric motors, causing the motor to fail prematurely. Therefore, the cavities within the electric motors are usually filled with uncontaminated motor oil to ensure their long-term successful operation.
The temperature of the motor oil varies as a result of the intermittent operation of the electric motor and the temperature of the fluid surrounding the electric motor. As the temperature of the motor oil rises, for instance, the oil tends to expand and the pressure within the motor tends to increase.
In most submergible pumping systems in use today, this motor oil is partially contained within a device commonly referred to as a motor protector. Motor protectors may serve several different functions. The motor protectors may serve to prevent well fluids and gases from contaminating the motor oil, transmit the torsional power produced by the electric motor to the pump, provide a storage reservoir of motor oil, provide for the expansion and contraction of the motor oil due to changes in temperature, and to equalize the internal pressure of the motor with the pressure of the surrounding subterranean fluids.
Several different approaches have been used to construct motor protectors. One type of motor protector is generally referred to as a “labyrinth” system. Labyrinth systems are exposed at one end to the subterranean fluids and to the electric motor at the other end. These systems retard the migration of subterranean fluid into the electric motor. However, the subterranean fluids can eventually migrate through the labyrinth path to enter the electric motor.
Another approach, referred to as “bladder” or “bag” system, utilizes an elastomeric barrier between the motor oil and the subterranean fluids. However, elastomeric bags suffer from several limitations. First, the repeated expansion and contraction of the elastomeric bag can cause the bag to split or crack under certain conditions. Of course, once an elastomeric bag splits or cracks it no longer protects the motor oil from contaminants which are then free to enter and ultimately damage the motor. Second, elastomeric bags tend to lose their elasticity due to various conditions which may be present in a wellbore. Once an elastomeric bag loses its elasticity, it can no longer expand and contract as needed to satisfy the requirements of the motor oil which it contains. Eventually the bag ruptures, leaving the contaminants free to attack the motor. Third, most elastomers cannot survive in environments where the temperature rises above about 400° F. Above that temperature, most elastomers become brittle causing the bag to break during expansion or contraction. Finally, elastomeric compounds currently used for motor protector bags tend to be relatively permeable as compared to the contaminants within the wellbore fluid. Many wells contain contaminants, such as hydrogen sulfide for instance, which can permeate the motor protector bag and attack the motor. In fact, certain contaminants, such as hydrogen sulfide, also tend to alter the chemistry of some elastomers, causing the elastomers to harden. Once the elastomer has hardened, the bag eventually breaks.
It would be advantageous to have a submergible pumping system that provides the desired functions of a motor protector but without the limitations of the labyrinth or bag systems.
SUMMARY OF THE INVENTION
The present invention features a system for absorbing the expansion and contraction of internal fluids of an electric motor. The system is comprised of a motor protector having: a first chamber in fluid communication with electric motor internal fluid, a second chamber in fluid communication with an environmental fluid, a communication passage in fluid communication with the first chamber and the second chamber, and a volume of gas between the electric motor internal fluid in the first chamber and the environmental fluid in the second chamber.
According to another aspect of the invention, a pumping system is featured that is designed for submersion in a production fluid disposed in a wellbore. The pumping system includes a submergible pump and a submergible motor coupled to the submergible pump and having an internal motor fluid. A motor protector is coupled to the submergible motor. The motor protector interior is exposed to the production fluid and to the internal motor fluid. Additionally, the motor protector has a gas pocket disposed intermediate to and in contact with the production fluid and the internal motor fluid.
According to another aspect of the invention, a method is provided for allowing the expansion and contraction of the internal fluids of an electric motor of a submergible system. The method includes the step of fluidicly coupling an electric motor internal fluid from an electric motor to a first chamber. The first chamber has sufficient volume to contain any expected increase in electric motor internal fluid volume resulting from an increase in electric motor internal fluid temperature due to operation of the electric motor and heat from the surrounding environment. Other steps of the method include: providing a pressure barrier that allows fluid from the surrounding environment to flow into a second chamber at a predetermined pressure, fluidicly coupling the first chamber and second chamber in such a manner as to allow a gas pocket to form between the first chamber and second chamber, and inserting a sufficient volume of gas to maintain a gas pocket between the first chamber and the second chamber at the operating depth of the submergible system and with the electric motor operating.
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Camco International Inc.
Fletcher Yoder & Van Someren
Mullins Burton
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