Tension thrust ESPCP system

[00002] 1. Field of the Invention

[00003] This invention relates in general to submersible well pumps, and in particular to devices for connecting and fastening shaft elements and other portions of submersible pump assemblies.

[00004] 2. Description of Prior Art

[00005] Electrical submersible pump (“ESP”) assemblies for pumping fluid from deep wells are typically made up of a series of interconnectable modular components including a motor, a seal section, and one or more pump sections with an associated fluid intake. One type of pump is a centrifugal pump made up of a large number of impellers and diffusers. Another type is a progressive cavity pump, which comprises a helical rotor rotated within an elastomeric stator having helical cavities. Each of the sections of these pumps includes an outer radial housing and interior shaft elements. The shaft elements of the different adjacent sections are connected to one another in coupling assemblies by some connection means. An example of connection means would be a set of matingly engaged splines.

[00006] During conventional ESP operation, the motor section drives the various shaft elements as well fluid is discharged to the ground surface. The shaft elements may be in clockwise rotation and the direction of thrust is downward, thus creating a compression load that is transmitted between the shaft elements. As a result of this compression, the splined connections between the shaft elements are forced together, keeping the connections intact. Thrust bearings in the seal section contain the downward thrust.

[00007] However, in situations where an ESP is operated in reverse rotation, the direction of thrust within the pump assembly is upward. In this situation, the shaft elements tend to move upward as well, creating a tension load. In a progressing cavity pump, particularly, this can cause the splined connections between the shaft elements to separate and become disengaged. Installing a physical stop element at the pump discharge can prevent this disengagement. However, stops present a significant drawback, as the placement of the stop must be matched in each individual ESP system, the weld integrity is critical, the skills involved in welding the stop must be duplicated at satellite locations, and the amount of upthrust is limited.

[00008] The invention provides a fastener for securing connected shaft elements within an electrical submersible pump assembly so that they do not become disengaged. The secured shaft elements can be from a seal section and a motor section, a motor section and a pump section, a pump section and a seal section, and so forth. The shaft sections are secured so as to support tension loading during reverse rotation as well as compression loading during clockwise rotation.

[00015] FIGS. 1A and 1B show a conventional progressing cavity (PC) pump assembly. While the preferred embodiment of the invention described herein relates to PC pump assemblies, the invention is not limited to use in PC pump assemblies only, and may be used in other ESP assemblies as well. In FIGS. 1A and 1B, the pump assembly has a pump assembly housing 5 consisting of a tubular pump housing 6, a flex shaft housing 7, and an intake housing 8. FIG. 1A shows an upper pump assembly section 10. FIG. 1B shows a lower pump assembly section 11 and an electric motor assembly 12. Referring to FIG. 1A, a string of production tubing 14 extends from a wellhead at ground surface (not shown) into a well. Tubular pump housing 6 is located at the lower end of production tubing 14. Pump housing 6 is connected to production tubing 14 with a threaded collar 18.

[00016] Within pump housing 6 is a metal rotor 20 with an exterior helical configuration. Rotor 20 has undulations with small diameter portions 22 and large diameter portions 24, which give rotor 20 a curved profile relative to axis 26. Rotor 20 orbitally rotates within an elastomeric stator 28 which is located in pump housing 6. Stator 28 has double or multiple helical cavities located along axis 26 through which rotor 20 orbits.

[00017] A rotor coupling 30 attached to the lower end of rotor 20 has a rotor receptacle 32 that receives the upper end of a metal flexible shaft 34. During normal clockwise rotor operation, gravity and the reaction force due to rotor 20 pumping fluid upward will keep rotor receptacle 32 engaged around the upper end of flexible shaft 34. Flexible shaft 34 flexes off of axis 26 at its upper end to allow rotor 20 to orbitally rotate.

[00018] Referring now to FIG. 1B, the lower end of flexible shaft 34 is received by a splined receptacle 36 on the upper end of a drive shaft extension 38. Drive shaft 40 extends upward from the top portion of seal section 42 and engages drive shaft extension 38 at drive shaft extension bottom receptacle 45. Drive shaft extension 38 is supported by bearings to keep it radially constrained. Drive shaft extension 38 is located within intake housing 8. The upper end of intake housing 8 is mounted to the lower end of flex shaft housing 7. The lower end of intake housing 8 connects to seal section 42.

[00019] The drive shaft 40 is powered by electric motor assembly 12, which is located in a motor assembly housing 41 releasably secured to the lower end of intake housing 8. Motor assembly 12 includes seal section 42 mounted to a gear reduction unit 48. Gear reduction unit 48 is mounted to an electric motor 50. An electrical power cable 52 connects to electric motor 50 and extends up alongside the pump assembly to the ground surface (not shown) for receiving electrical power. Seal section 42 seals well fluid from the interior of electric motor 50 and also equalizes the pressure differential between the lubricant in motor 50 and the pump assembly exterior.

[00020] FIGS. 2A and 2B show engaged coupling assemblies for shaft elements within the pump assembly. FIG. 2A shows the upper end of flexible shaft 34 engaged with rotor receptacle 32 attached to the lower end of rotor 20. FIG. 2B shows the lower end of flexible shaft 34 engaged with drive shaft extension top receptacle 36 attached to the upper end of drive shaft extension 38.

[00021] Referring now to FIG. 2A, rotor receptacle 32 has a bore therewithin with longitudinal internal splines 54 extending downward that are complimentary in size and shape to interfit with the longitudinal external splines 56 of the upper end of flexible shaft 34. Rotor receptacle 32 and flexible shaft 34 have been axially aligned with one another and moved toward engagement. The splined upper end of flexible shaft 34 is inserted into rotor receptacle 32. As a result, the longitudinal external splines 56 at the end of flexible shaft 34 become engaged with the complementary longitudinal internal splines 54 within rotor receptacle 32 to transmit torque.

[00022] Referring now to FIG. 2B, drive shaft extension top receptacle 36 has a bore with longitudinal internal splines extending upward that are complimentary in size and shape to interfit with the longitudinal external splines of the lower end of flexible shaft 34. Drive shaft extension top receptacle 36 and flexible shaft 34 have been axially aligned with one another and moved toward engagement. The splined lower end of flexible shaft 34 is inserted into drive shaft extension top receptacle 36. As a result, the longitudinal external splines at the end of flexible shaft 34 become engaged with the complementary longitudinal internal splines within drive shaft extension top receptacle 36 to transmit torque.

[00023] Drive shaft extension bottom receptacle 45 has a bore with longitudinal internal splines extending downward that are complimentary in size and shape to interfit with the longitudinal external splines of the upper end of drive shaft 40. Drive shaft extension bottom receptacle 45 and drive shaft 40 have been axially aligned with one another and moved toward engagement. The splined upper end of drive shaft 40 is inserted into drive shaft extension bottom receptacle 45. As a result, the longitudinal external splines at the end of drive shaft 40 become engaged with the complementary longitudinal internal splines within drive shaft extension bottom receptacle 45 to transmit torque.

[00024] Referring to FIG. 3, rotor 20 is secured by threads 66 to rotor coupling 30. Fastener apertures 58 are positioned such that a fastener 60 can be closely inserted into each fastener aperture 58 and disposed through the walls of rotor receptacle 32 to be secured to the portion of flexible shaft 34 within rotor receptacle 32, thus securely interconnecting flexible shaft 34 to rotor receptacle 32. Referring to FIG. 4, fastener 60 preferably comprises a key 62 and a screw 64. A mating recess 68 is formed on the end of flexible shaft 34 for alignment with fastener aperture 58. Key 62 extends through fastener aperture 58 into recess 68. Key 62 is a cylindrical member with a cavity 70 for receiving a screw 64. Screw 64 secures in a threaded hole 72 in the end of shaft 34. Axial tension between receptacle 32 and flexible shaft 34 transmits through key 62, and not through screw 64.

[00025] During initial construction and assembly, some of the adjacent shaft elements within the pump assembly may be interconnected and fastened to one another. For example, rotor 20, flexible shaft 34, and drive shaft extension 38 may be connected with keys 62, then inserted into production tubing 14, pump housing 6, flex shaft housing 7, and intake housing 8 prior to delivery to the well site. Seal section 42 will normally be connected to intake housing 8 or flex shaft housing 7 at the well site. An access port such as hole 74 (FIG. 3) may be located in some section of housing, for example, the housing 7 of flexible shaft 34 or the housing of seal section 42 at the upper end, to allow keys 62 and screws 64 to be installed.

[00026] In operation, motor 50 is supplied with power, causing drive shaft 40 to rotate, which in turn rotates rotor 20. Thrust is downward as well fluid is pumped upward through production tubing 14. If motor 50 is shut off, the weight of the fluid in production tubing 14 will fall, causing reverse spinning of rotor 20. Rotor 20 will tend to move upward, causing tension in the couplings to occur. The tension is then transmitted through keys 62, preventing any of the coupling from separating. An upthrust bearing in the seal section shaft (not shown) prevents the shaft from becoming disengaged with the driver components. The same axial tension can occur if motor 50 is powered in reverse rotation.

[00027] The invention has significant advantages. By securely interconnecting the adjacent shaft elements in the pump assembly, the upthrust forces of the rotor during counterclockwise motion are transferred to the seal section shaft and the upthrust bearing within the seal section. Thus, the need for a rotor stop is eliminated, which simplifies field use of ESP systems and reduces risk of downhole failures.

[00028] While the invention has been shown in only one of its forms, it should be apparent to those skilled in the art that it is not so limited but is susceptible to various changes without departing from the scope of the invention. For example, not all of the couplings need to be splined types; rather, some could be secured other ways, such as by threads.