SUBMERSIBLE PUMPS

RELATED APPLICATIONS

[0001 ] This patent application claims the benefit of priority to U.S. Provisional Patent Application No. 61/870,780 to Cheah, filed August 27, 2013, and herein incorporated by reference in its entirety.

BACKGROUND

[0002] When conventional electric submersible pumps (ESPs) operate, the rotating impeller thrusts the fluid being pumped, creating an opposite reactionary force that is conventionally transferred in its entirety to the rotating shaft that drives the impeller. When a fluid is being pumped "upwards" from the impeller, the pumping creates an opposite downthrust on the impeller and its shaft that must be supported or counteracted, for example, by a downthrust washer. Likewise, depending on the flow rate and pressure generated, the impeller may be pushed upwards instead of downwards, conventionally counteracted by an upthrust washer.

[0003] These thrust washers eventually wear away after long operation, and downthrust washers take the brunt of forces generated during normal operation of a single ESP, or an ESP stack. When compression-style pumps are in tandem operation (two, three, four or more pump sections ganged together in series), then the forces are additive and the impeller stack and shafts can deflect under the load caused by excessive downthrust over multiple units. This increased load and shaft deflection can compromise longevity and cause problems, such as rubbing between impeller and diffuser.

SUMMARY

[0004] An example system includes an electric submersible pump (ESP) for artificial lift in a well, a shaft in the ESP, a tapered sleeve bearing slidable along the shaft, a tapered bushing to receive the tapered sleeve bearing along a mutual taper interface, and an elastic member in contact with the tapered sleeve bearing for engaging the tapered sleeve bearing with the tapered bushing in response to an axial force on the tapered sleeve bearing. In an implementation, a self-compliant bearing system for a shaft includes a sleeve bearing for the shaft, a bushing to mate with the sleeve bearing at tapered surfaces of the sleeve bearing and the bushing, and a spring to engage the sleeve bearing with the bushing when the shaft is under an axial load. An example apparatus includes an electric submersible pump (ESP), and a self- compliant bearing system in the ESP capable of adapting a degree of load- bearing capacity of the ESP in response to different thrust forces in the ESP. This summary is provided to introduce a selection of concepts that are further described below in the detailed description. This summary is not intended to identify key or essential features of the claimed subject matter, nor is it intended to be used as an aid in limiting the scope of the claimed subject matter. BRIEF DESCRIPTION OF THE DRAWINGS

[0005] Certain embodiments of the disclosure will hereafter be described with reference to the accompanying drawings, wherein like reference numerals denote like elements. It should be understood, however, that the accompanying figures illustrate the various implementations described herein and are not meant to limit the scope of various technologies described herein.

[0006] Fig. 1 is a diagram of an example ESP including a self-compliant bearing system, with the impeller in a lifted position.

[0007] Fig. 2 is a diagram of the example ESP with the impeller in a downthrust position, and the self-compliant bearing system engaged to dissipate downthrust.

[0008] Fig. 3 is a diagram of example downthrust forces in the example self-compliant bearing system, as transferred from tapered sleeve to tapered bushing and converted in part from an axial force to a radial force.

[0009] Fig. 4 is a diagram of the example ESP with the impeller in an upthrust position and the self-compliant bearing system disengaged.

[0010] Fig. 5 is a diagram of an example top side section of the example

ESP providing a shaft stop for instances of the example self-compliant bearing system.

[001 1 ] Fig. 6 is a flow diagram of an example method of increasing the lifespan of an ESP via a self-compliant bearing system. DETAILED DESCRIPTION

[0012] This disclosure describes example embodiments of a self- compliant bearing system for electric submersible pumps (ESPs). In the following description, numerous details are set forth to provide an understanding of some embodiments of the present disclosure. However, it will be understood by those of ordinary skill in the art that the system and/or methodology may be practiced without these details and that numerous variations or modifications from the described embodiments may be possible.

[0013] Representative implementations of the self-compliant bearing systems can engage for action, or disengage, in response to various different thrust forces acting on the impeller of the ESP. When engaged, the bearing system has tapered sleeve-and-bushing components that can convert axial load on the impeller into a radial force that can be dissipated into the diffuser housing, sparing the thrust washers. During neutral rotation, the example bearing system can float the impeller to avoid contact with both downthrust and upthrust washers, increasing the lifespan of the ESP. In an ESP stack, multiple instances of the self-compliant bearing system can alleviate downthrust of the serially connected impellers.

[0014] Fig. 1 shows pump components of an example ESP 100 including an example self-adjusting ("self-compliant") sleeve-and-bushing-bearing system 102. The example ESP 100 is shown in neutral or "lifted" position, in which neither downthrust forces nor upthrust forces dominate the impeller of the ESP 100.

[0015] The example ESP 100 of Fig. 1 , which provides one example setting for the self-compliant sleeve-and-bushing bearing system 102, may include an impeller 104, diffuser (and bearing housing) 106, and impeller shaft 108. One or more downthrust washers 110 between impeller 104 and diffuser 106 bear the reactionary thrust of the main pumping action of the ESP 100. One or more upthrust washers (rings) 112 and pads 114 may cushion the impeller 104 when the impeller 104 is forced away from the downthrust washer 110 due to various pressure circumstances. These components included in a pump section of the example ESP 100 may recur in multiple adjacent instances of the ESP 100, axially stacked together ("ESP stack") for increased pumping capacity.

[0016] The pump section of the example ESP 100 just described provides a representative example setting in which the self-compliant bearing system 102 can be used. The self-compliant bearing system 102 can also be used in many other circumstances and different types of apparatuses that include a shaft 108 that is bearing a changeable load along an axial vector.

[0017] In an example implementation, the self-compliant bearing system 102 includes a (e.g., keyless) tapered sleeve bearing 116 located around the impeller shaft 108, and axially limited in motion along the shaft 108 by one or more spacers 118. The tapered sleeve bearing 116 fits inside a complementary tapered bushing 120, which in one implementation is immobile and fastened to diffuser housing structures'! 06 that can provide some bearing support. The tapered sleeve bearing 116 slides along the shaft 108 and can slide axially inside the complementary tapered bushing 120 until the tapered sleeve bearing 116 and the complementary tapered bushing 120 engage their corresponding tapered surfaces. Upon engagement, the first taper of the tapered sleeve bearing 116 and the second taper of the complementary tapered bushing 120 form a bearing interface that supports the shaft 108 radially and also supports against a downward (or baseward) axial load being borne by the shaft 108, converting some of the axial downthrust to a radial force instead.

[0018] The tapered sleeve bearing 116 and the complementary tapered bushing 120 can form a system that is biased by an elastic member, such as a spring 122 between the impeller hub 124 and the tapered sleeve 116, as shown in Fig. 1 . The spring 122 is self-compliant to expand or contract in response to different ESP circumstances, such as when the ESP pump 100 is in neutral, upthrust, and downthrust conditions, thus allowing the self- compliant bearing system 102 to engage and disengage, and also allowing the impeller to float when forces are neutral, to avoid unnecessary wear on the thrust washers 110, 112, & 114.

[0019] The impeller hub 124, the spring 122, and the tapered sleeve bearing 116 can be attached together as an axial unit with components that slide along the shaft 108, with the spring 122 or other elastic member providing some elasticity and "give" (compression and expansion) between the moving impeller hub 124 and the moving tapered sleeve bearing 116.

[0020] In an implementation, the example self-compliant bearing system 102 forms an automatically engageable bearing for the impeller 104 under load, in the sense that the bearing support provided goes in and out of service depending on the current thrust forces in the pump. Moreover, under non-load conditions, the example self-compliant bearing system 102 may allow the impeller 104 to float, without contacting either the one or more downthrust washers 110 or the one or more upthrust washers 112 or pads 114, thereby increasing the lifespan of the ESP 100, and particularly increasing the lifespan of the various thrust washers 110, 112, & 114.

[0021 ] In an implementation, a system includes the ESP 100 for artificial lift in a well, a shaft 108 in the ESP 100, a tapered sleeve bearing 116 slidable along the shaft 108, a tapered bushing 120 to receive the tapered sleeve bearing 116 along a mutual taper interface, and an elastic member 122 in contact with the tapered sleeve bearing 116 for engaging the tapered sleeve bearing 116 with the tapered bushing 120 in response to an axial force on the tapered sleeve bearing 116.

[0022] The example system may include an impeller 104 rotationally driven by the shaft 108. The elastic member 122 can apply an axial bias between the impeller 104 and the tapered sleeve bearing 116. The elastic member 122 may be a spring 122 around the shaft 108, or a spring-loaded shaft, with the spring 122 biased between the impeller 104 and the tapered sleeve bearing. Compressibility of the spring 122 can be set or selected to engage the tapered sleeve bearing 116 and the tapered bushing 120 with each other along the mutual taper interface when the impeller 104 receives a sufficient downthrust force. The compressibility of the spring 122 can also be set or selected to disengage the tapered sleeve bearing 116 from the tapered bushing 120 when the impeller 104 receives an upthrust force. The compressibility of the spring 122 can also be set or selected to disengage the tapered sleeve bearing 116 from the tapered bushing 120, floating the impeller to avoid contact with a downthrust washer 110 and contact with an upthrust washer 112 when forces on the impeller 104 are neutral.

[0023] The mutual taper interface between tapered sleeve bearing 116 and tapered bushing 120 transmits a component of the axial force on the tapered sleeve bearing 116 radially outward through the tapered bushing 120 to a diffuser 106 or a housing of the ESP 100.

[0024] The self-compliant bearing system 102 thus dissipates some of the downthrust forces generated within the example ESP 100 through a sideways force vector that is not coaxial with the impeller shaft 108. The example self- compliant bearing system 102 can also limit gross axial movement or play of the impeller shaft 108 (or other shaft) in either axial direction, to decrease the danger of metal-to-metal rubbing between the impeller 104 and the stationary diffuser 106 or its housing, increasing the lifespan of the ESP 100 or ESP stack. Further, the example self-compliant bearing system 102 also decreases over-reliance on thrust washers, such as the downthrust washers 110 and the upthrust washers 112. The self-compliant bearing system 102 can prevent concentrating too much axial downthrust upon a given span of the shaft 108, which can cause spans of the shaft 108 or other hardware parts to deflect or bend. In an implementation, the self-compliant bearing system 102 is particularly applicable to mixed-flow ESPs 100, with compression-style construction.

[0025] In an implementation, as introduced above, the example self- compliant bearing system 102 can provide three operating positions or states, including a downthrust position, an upthrust position, and a neutral position.

[0026] For the neutral or "lifted" position, when the ESP 100 is neutral or not pumping very hard, the spring 122 disengages the tapered sleeve bearing 116 from the complementary bushing 120, and the spacers 118 maintain support of the shaft 108 (e.g., radial support), while the impeller 104 floats without significant friction contact with either the downthrust washers 110 or the upthrust washers 112 & 114.

[0027] In an implementation, during upthrust (the upthrust position of the self-compliant bearing system 102), the self-compliant bearing system 102 may disengage, as facilitated by the spring 122 or a spring-loaded shaft 108, allowing the impeller 104 to either float or ride the upthrust washers 112 and pads 114.

[0028] During downthrust (the downthrust position of the self-compliant bearing system 102), when the example ESP 100 is performing its most normal task of heavy pumping, the downthrust forces move the impeller 104, and cause the spring 122 to pull the tapered sleeve bearing 116 along the shaft 108 into engagement with the complementary tapered bushing 120. When the tapered sleeve bearing 116 and the tapered bushing 120 are engaged, then some of the downthrust load on the shaft 108 gets transmitted sideways through the tapered support and into the surrounding diffuser 106, instead of solely to the downthrust washers 110.

[0029] In a stack of ESPs 100, the impeller 104 of a next adjacent ESP section superior to an example bearing system 102 may load the spacer 118 below itself during downthrust, overcoming the expansive force of the spring 122 below, and compressing the spring 122 to the point where the corresponding tapered sleeve bearing 116 sliding on the shaft 108 engages its complementary tapered bushing 120. The impeller 104 directly below the tapered sleeve bearing 116 also pulls the inferior end of the same spring 122, in turn pulling the given tapered sleeve bearing 116 into engagement with the complementary tapered bushing 120. In other words, in a stack of ESP pumps 100, each corresponding self-compliant bearing system 102 of each section engages for action during downthrust. At this point of engagement, each self-compliant bearing system 102 joins the spacers 118 of the ESP stack in supporting the shaft 108 (radially) and in taking a significant amount of the axial thrust load off of the downthrust washers 110 of each ESP section. The multiple self-compliant bearing systems 102 dissipate some of the total downthrust force in a radial direction instead of an axial direction, to spread the downthrust forces more widely around the diffuser housing 106 instead of concentrating the axial support for the downthrust forces only at diffuser structures 106 that are near the downthrust washers 110.

[0030] In an implementation, the spring 122 is nominally in a slightly compressed state or a neutral state when the impeller 104 is neutral, that is, when neither downthrust nor upthrust forces are being generated by the impeller 104.

[0031 ] When the ESP pump 100 is not running and in a neutral or lifted position, a hard stop for items sliding on the shaft 108, such as a two-piece ring on the shaft 108, can support an impeller 104 or a stack of impellers 104 and the expansive property of the spring 122 in turn can push up on the impeller stack 104 and sleeve bearing(s) 116. In a stack of multiple ESP's 100 in series, all impellers 104 in the stack of ESPs 100 are then lifted in series by the springs 122 of the self-compliant bearing systems 102 in each ESP, and the series of impellers 104 "floats" without the impeller 104 contacting either downthrust washers 110 or upthrust washers 112 & 114, but yet in a state of slight compression. When the ESP pump 100 is neutral in this manner, the top and bottom ends of the shaft 108 are provided some free play and have room to move in either direction axially.

[0032] Fig. 2 shows the example ESP 100 in a downthrust position 200. The fluid thrust being generated by the impeller 104 pushes the impeller 104 towards the base side 202 of the single ESP 100 or the ESP stack. In an implementation, a given impeller 104 moves toward the downthrust washers 110 and in turn pulls the spring 122 or allows the spring 122 to decompress, which moves the tapered sleeve bearing 116 above the impeller 104 to engage the complementary tapered bushing 120. Depending on implementation, this engagement between tapered sleeve bearing 116 and complementary tapered bushing 120 may prevent the impeller 104 from moving further downward.

[0033] In an implementation, the downthrust force from an "n + 1 " ESP pump stage 100 (i.e., from the impeller 104 of the ESP section "above" a given self-compliant bearing system 102) gets transferred to the "nth"-stage self-compliant bearing system 102 at hand. The impeller 104 below the given self-compliant bearing system 102 may also transfer downthrust force to the given self-compliant bearing system 102 through the spring 122 between them, depending on implementation.

[0034] In an implementation, the self-compliant bearing system 102 may include an abrasion-resistant zirconia (ARZ) ceramic bearing 116, bushing 120, and/or bearing housing, which may also be part of the diffuser 106. Transferring and converting the downthrust to the bearing housing in this manner reduces the thrust load on the shaft 108 and limits deflection.

[0035] Fig. 3 shows the transfer of force between an example tapered sleeve bearing 116 and a complementary tapered bushing 120. A component vector of the thrust force received 302 at the self-compliant bearing system 102 is dissipated to the bearing housing 304 and in turn to the diffuser housing via a radial vector 306, as shown. This relieves some of the axial thrust load 308 from the underlying shaft 108, and also allows the shaft 108 and supporting structures to support more weight, and more thrust load.

[0036] Fig. 4 shows an upthrust position 400 of the impeller 104 of the example ESP 100, and the corresponding upthrust behavior of the example self-compliant bearing system 102. In a stack of ESPs 100, in the upthrust position 400, all of the impellers 104 are lifted up by the upthrust forces. In an implementation, the springs 122 of the self-compliant bearing systems 102 in the entire stack of impellers 104 remain in some compression and may coerce the impellers 104 away from full friction against the upthrust washers 112 and pads 114. During such an upthrust scenario 400, each tapered sleeve bearing 116 and each corresponding complementary tapered bushing 120 are disengaged, but the spacers 118 still provide radial bearing support to the shafts 108 and impellers 104.

[0037] Fig. 5 shows a top section 500 of the example ESP 100. On the top side of the ESP pump 100, the spring 122 is compressed and pushes against spacers 118 abutting one or more stops 502 near the top of the shaft 108, and the spring 122 also pushes the impeller 104 downward from the top, in a direction 504 away from friction contact with upthrust washers 112. The stop 502 may be a two-piece ring and compression nut and sleeve, for example.

[0038] The self-compensating action of the spring-loaded self-compliant bearing system 102 can increase the recommended operating range of an ESP 100 or an ESP stack to a higher flow rating by maintaining floating impellers 104 that are not in friction contact with downthrust washers 110 and upthrust washers 112 while thrusting fluid in the floating state.

Example Method

[0039] Fig. 6 shows an example method 600 of increasing the lifespan of an ESP via a self-compliant bearing system. In the flow diagram, the operations are described by individual blocks.

[0040] At block 602, an ESP is constructed to include a tapered sleeve and bushing system on the shaft for alleviating some axial downthrust forces on a thrust washer.

[0041 ] At block 604, a spring force is applied to the tapered sleeve to bias the tapered sleeve for engagement with the bushing during the axial downthrust, to convert some of the axial downthrust to a radial force.

Conclusion

[0042] Although a few embodiments of the disclosure have been described in detail above, those of ordinary skill in the art will readily appreciate that many modifications are possible without materially departing from the teachings of this disclosure. Accordingly, such modifications are intended to be included within the scope of this disclosure as defined in the claims.