Wells – Processes – Separating material entering well
Reexamination Certificate
1999-12-02
2001-07-10
Schoeppel, Roger (Department: 3672)
Wells
Processes
Separating material entering well
C166S066400, C166S104000, C166S105500, C166S117700
Reexamination Certificate
active
06257333
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates generally to a system and method for displacing fluids from a wellbore. More specifically, the present invention relates to a submergible pumping system utilizing a submergible electric motor, a progressing cavity pump, and a reverse flow gas separator to reduce the amount of gas pumped by the system.
BACKGROUND OF THE INVENTION
A variety of tools and other equipment are used in downhole, wellbore environments. For example, a progressing cavity pump may be utilized in producing petroleum and other useful fluids from production wells. When a progressing cavity pump system is used, production tubing is disposed within a wellbore to extend through the wellbore to the progressing cavity pump system disposed at a specific location within the well. The progressing cavity pump can be deployed or retrieved through the center of the production tubing, via a wireline or coiled tubing.
In operation, fluids contained in an underground formation enter the wellbore via perforations formed through a wellbore casing adjacent to a production formation. Fluids, such as petroleum, flow from the formation and collect in the wellbore. A progressing cavity pump moves the production fluids upwardly through the production tubing to a desired collection point.
A progressing cavity pump, consists of a single helical rotor which rotates inside a double internal helical stator. The rotor is typically made from a high strength steel while the stator is molded of an elastomeric material. When the rotor is placed within the stator, two chains of spiral cavities are formed. As the rotor turns, the cavities spiral up the length of the pump. Fluid within the cavities is carried along as the cavities progress up the length of the pump. Hence the name, progressing cavity pump.
A progressing cavity pumping system, typically includes a motor drivingly coupled to a progressing cavity pump. For oil field applications, the motor may be located on the surface and drivingly coupled from the surface down to a submergible progressing cavity pump in the wellbore. This is an example of a top-driven pumping system. Alternatively, the motor may be placed in the wellbore as part of an electrical submergible progressing cavity pumping system. Electric power is provided to a submergible electric motor drivingly coupled to a progressing cavity pump. The fluid displaced by the pump is communicated to the surface through production tubing. Spatial considerations among the pump, production tubing and motor encourage placement of the submergible electric motor below the progressing cavity pump. Such a system is an example of a bottom-driven pumping system.
A significant advantage of the progressing cavity pump is that the presence of gas in the fluid will not cause the progressing cavity pump to cavitate, as in other types of pumps. However, free gas in the fluid stream can occupy space in the cavities that could otherwise have been filled by desired liquids, such as oil. This reduces the pumps useful capacity and causes apparent pump inefficiency.
Rotary gas separators have been used to reduce the concentrations of gas in the fluid stream of submergible pumping systems utilizing other types of pumps, such as centrifugal pumps. Rotary gas separators use centrifugal force and differences in the specific gravities of fluids to separate a fluid into its constituent gases and liquids. Typically, the drive train of a submergible electric pumping system is coupled to the rotary gas separator. However, the drive train of a progressing cavity pump tends to produce oscillations and gyrations that propagate through the drive train during operation. Those oscillations and gyrations increase the stress on bearings supporting the drive train within the rotary gas separator and lead to a higher likelihood of bearing failure.
Additionally, the orientation of the motor, pump, and fluid intake in a bottom-driven system increases the complexity of using a rotary gas separator. Typically, in a bottom-driven system the system is oriented with the motor at the bottom of a tool string. The motor is coupled to the progressing cavity pump through a drive train. Fluid enters the system through a separate fluid intake that is located between the motor and the progressing cavity pump. Thus, the drive train coupling the motor to the progressing cavity pump must pass through the fluid intake to the progressing cavity pump. Consequently, the fluid intake and any other element between the motor and pump must provide structural support to the motor in order for the motor to provide torque to the pump. The structural member and torque requirements in a bottom-driven system, along with the oscillations and gyrations produced in a progressing cavity pumping system, must be factored into the design of any system incorporating a rotary gas separator into the tool string between the motor and pump.
Therefore, it would be advantageous to have a system that could reduce the quantity of gas pumped by a submergible electric progressing cavity pumping system without the use of a rotary gas separator.
SUMMARY OF THE INVENTION
The present invention features a submergible pumping system for displacing wellbore fluids. The system is comprised of a fluid intake and a submergible electric motor drivingly coupled to a progressing cavity pump. The fluid intake has a hollow interior defined by a thick-walled section. A plurality of fluid passageways extend through the thick-walled section and are oriented to create a reversal in fluid flow as fluid is drawn into the fluid intake.
According to another aspect of the invention, a pumping system for displacing wellbore fluids comprises a submergible electric motor, a progressing cavity pump operatively coupled to the submergible electric motor and disposed above the submergible electric motor when the system is oriented vertically, and a fluid intake disposed between the pump and motor. The fluid intake includes a body, a hollow interior within the body, and a sloped fluid passageway. The sloped fluid passageway extends through the body into communication with the hollow interior. When the system is oriented vertically the lowest point on an exterior end of a sloped fluid passageway is higher than the highest point on an interior end of the sloped fluid passageway.
According to another aspect of the present invention, a method of displacing wellbore fluids from a well is featured. The steps of the method are comprised of: drawing a wellbore fluid in a first direction along a fluid intake of a submergible pumping system, abruptly changing the flow of wellbore fluid to a second direction as the wellbore fluid enters the intake, maintaining a sufficient fluid flow rate, and maintaining a sufficient change from the first direction to the second direction to induce separation of a gas from the wellbore fluid.
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Mann Jay S.
Straub Peter H. G.
Camco International Inc.
Fletcher Yoder & Van Someren
Schoeppel Roger
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