Patent Application
20090159262
1. Field of Invention
The present disclosure relates to downhole pumping systems submersible in well bore fluids. More specifically, the present disclosure concerns recirculating a portion of the flow pumped by a submersible pump of a downhole pumping system to the intake of the pumping system.
2. Description of Prior Art
Submersible pumping systems are often used in hydrocarbon producing wells for pumping fluids from within the wellbore to the surface. These fluids are generally liquids and include produced liquid hydrocarbon as well as water. One type of system used in this application employs an electrical submersible pump (ESP). ESPs are typically disposed at the end of a length of production tubing and have an electrically powered motor. Often, electrical power may be supplied to the pump motor via wireline. Typically, the pumping unit is disposed within the well bore just above where perforations are made into a hydrocarbon producing zone. This placement thereby allows the produced fluids to flow past the outer surface of the pumping motor and provide a cooling effect.
In some situations the submersible pumping systems are disposed in a wellbore where the pump intale is below the perforations. In this situation, fluid flowing from the producing zone reaches the pump inlet before passing by the motor. As such the produced fluid is pumped to the surface without first cooling the motor. To provide cooling to the pump motor, an ESP system may comprise multiple pumps and a recirculation line that directs flow from the discharge of a lower pump to below the motor.
The present disclosure includes a downhole submersible pumping system disposable in a cased wellbore. The system comprises a lower pump an upper pump, a pump motor in cooperation with the lower pump and upper pump, a seal section, a recirculation coupling connected on one end to the lower pump discharge and on the other end to the upper pump intake. The system also includes a recirculation line having an intake in fluid communication with the recirculation coupling and an exit configured to discharge fluid from the recirculation line onto the pump motor. The recirculation coupling is formed first as a modular independent component and then connected to the lower pump and upper pump. The cooperation between the pump motor and pumps may comprise a shaft extending from the pump motor to both pumps and configured to rotate impellers disposed within the pumps. The recirculation coupling is configured to receive fluid discharged from the lower pump and to direct a portion of the received fluid to the upper pump intake and the remaining portion of the received flow to the recirculation line. Optionally, the lower pump and upper pump originally comprise a part of a multi-stage pumping system and wherein the multi-stage pumping system is retrofitted to include the recirculation coupling between the lower pump and the upper pump.
Some of the features and benefits of the present invention having been stated, others will become apparent as the description proceeds when taken in conjunction with the accompanying drawings, in which:
While the invention will be described in connection with the preferred embodiments, it will be understood that it is not intended to limit the invention to that embodiment. On the contrary, it is intended to cover all alternatives, modifications, and equivalents, as may be included within the spirit and scope of the invention as defined by the appended claims.
The present invention will now be described more fully hereinafter with reference to the accompanying drawings in which embodiments of the invention are shown. This invention may, however, be embodied in many different forms and should not be construed as limited to the illustrated embodiments set forth herein; rather, these embodiments are provided so that this disclosure will be through and complete, and will fully convey the scope of the invention to those skilled in the art. Like numbers refer to like elements throughout.
The present disclosure provides embodiments of a downhole submersible pumping system for producing fluids from within a wellbore up to the surface. More specifically, the downhole submersible pumping system described herein includes a system for recirculating flow from the pump discharge to below the pump motor. The recirculating fluid flows across the pump motor and absorbs heat therefrom as the fluid is drawn to the pump inlet.
Referring now to
In one embodiment, both the upper and lower pumps (28, 29) comprise independent stand alone pumps that are coaxially connected by the coupling 31 as shown. For the purposes of this disclosure, the term “independent stand alone pumps” refers to standard submersible pumps used for pumping fluids from within a wellbore. Thus, each the upper and lower pump (28, 29), although combined into a single unit, are capable of pumping from within a wellbore without the need for an additional pump. Similarly, in one embodiment the recirculation coupling 31 is also a modular self standing unit formed independent of either the upper or lower pump (28, 29) and later affixed to these pumps as illustrated in
In one mode of operation of the electrical submersible pumping system 20 of
The motor 22 provides a rotational motive force on the pumps (28, 29) for rotating impellers disposed therein thereby urging production fluid into the pumping system 20. In this embodiment a single shaft (not shown in
The embodiment of
The portion of the produced fluid that flows into the pump intake 32 is urged upwards from the lower pump 29 through the exit of the recirculation coupling 31 into the intake of the upper pump 28. The upper pump 28 further pressurizes the production fluid where it is discharged from the upper pump into associated production tubing 18 for delivery to the Earth's surface. Thus the pump intake 32 serves as a pump system fluid inlet for allowing fluid flow to the intake of both the lower pump 29 and the upper pump 28.
A single integral shaft 27 is shown coaxially disposed within the upper pump 28 and lower pump 29. The shaft 27 is coupled to impellers 37 disposed within the upper pump 28 and optionally a shaft bearing 84 supports and centers the shaft 27 within the upper pump 28. The lower portion of the shaft 27 resides within the lower pump 29 also optionally centered within the lower pump 29 by a corresponding shaft bearing 87. A converging conical plenum 86 describes the space where the lower pump discharge meets the recirculation coupling 31 intake. The recirculation tube 38 is shown connected on its first end to a port 41 formed through the wall of the recirculation coupling 31. An optional orifice 47 may be included for regulating the recirculation fluid flow rate. As shown in the recirculation tube 38 is disposed in the recirculation tubing 38, however it can also be positioned within the port 41. Establishing the orifice size and type varies the pump design and application, however sizing the orifice is within the scope of those skilled in the art. Alternatively, a threaded fitting may be employed for attaching the tubing 38 to the port 41. In such an embodiment, an orifice may be mounted into the fitting. The orifice 47 may comprise a “ferulle” type fitting having a sloping reduced inner diameter. The orifice 47 may also comprise a plate with a reduced diameter opening within the plate for restricting and regulating fluid flow.
With reference now to
Referring now to
In this view, a port 72 is shown formed through the wall of the housing 55 thereby providing for fluid communication between the annular space 70 and the inner circumference of the recirculation tube 74. Accordingly, the port 72 may be configured as a constriction to regulate flow therethrough to supply a requisite amount of cooling fluid from within the annular space to the outer surface of the pump motor 22. The constriction dimensions would depend on the discharge flow of the lower pump 56 and the cooling requirements of the pump motor 22. It is believed it is well within the capabilities of those skilled in the art to create an appropriately sized port to meet these parameters. Optionally, an orifice 75 may be included within the tube 74 for regulating the recirculation flow. Referring now to the lower end of the recirculation coupling 54, the upper end of the lower pump section is shown threadingly coupled thereto.
One of the many advantages of the pumping system disclosed herein is the modular ability to create the pumping system from independent stand alone elements. Previously known pumping systems having a recirculation element or recirculation function required a dedicated discharge head in a corresponding recirculation pump that directed recirculation flow upstream of the pump motor. The modular configuration disclosed herein comprises independent stand alone elements that do not require the dedicated machining and design of the recirculation discharge head. The recirculating pumping system described herein can easily be produced by using off the shelf components that do not require specific machining.
In the embodiments discussed, stage compression of the lower pump may be achieved by use of a compressible member, i.e., a wave washer that would be compressed to apply a force to a diffuser stack and would accommodate differences in diffuser stack and/or housing lengths due to manufacturing tolerances. Also, a bearing spider may be installed for compressing the diffuser stack in the lower pump.
In one optional embodiment, a recirculation system of the present disclosure is formed by retrofitting a multi-stage pumping system. A multi-stage pumping system includes two or more dedicated individual pumps coaxially disposed at different locations along the axis of the pumping system. A recirculation coupling in accordance with that disclosed herein may be inserted in the space between the severed pumps. In this embodiment the circulation coupling will have its intake and exit coupled with the respective severed ends of the multistage pumping system. By coupling the recirculation coupling with the severed ends, an integrated recirculation pumping system may be formed for insertion into and operation within a wellbore. A retrofit kit could be developed that includes all of the components needed to convert an on the shelf standard pump for recirculation applications.
It is to be understood that the invention is not limited to the exact details of construction, operation, exact materials, or embodiments shown and described, as modifications and equivalents will be apparent to one skilled in the art. In the drawings and specification, there have been disclosed illustrative embodiments of the invention and, although specific terms are employed, they are used in a generic and descriptive sense only and not for the purpose of limitation. Accordingly, the invention is therefore to be limited only by the scope of the appended claims.
