BACKGROUND

[0001] This section provides background information to facilitate a better understanding of the various aspects of the disclosure. It should be understood that the statements in this section of this document are to be read in this light, and not as admissions of prior art.

[0002] When pumping downhole fluids with an electric submersible pump, a variety of hydraulic forces act on various components. For example, impellers in submersible pumps tend to create large reaction forces that act in a direction opposite to the direction of fluid flow. The large reaction forces are typically resisted by, for example, a thrust washer in each stage of a floater style pump or by a motor protector thrust bearing in compression style pumps. The thrust created by the impeller in each stage of a submersible pump can be problematic in a variety of submersible pump types, including pumps with radial flow stages, mixed flow stages and axial flow stages.

SUMMARY

[0003] In accordance to one or more aspects an electric submersible pump (ESP) includes a radial flow, mixed flow, or axial flow pump stage having an impeller forming a fluid path from an intake to an outlet, a balance chamber formed between the impeller and a diffuser, a recirculation hole in fluid communication with the balance chamber and one of the intake and the outlet and a balance passageway in communication with balance chamber and the other of the inlet and the outlet, the balance passageway including a radial clearance formed between an outer surface of a balance ring extending from one of the impeller and the diffuser and an inner surface of a balance bore of the other of the impeller and the diffuser. In accordance to aspects a feature may be disposed at the radial clearance to change the size of the radial clearance based on the axial spacing of the impeller and the diffuser relative to one another. An axial flow submersible pump in accordance to an aspect includes an impeller forming an axial fluid path extending from an intake to an outlet and a balance chamber formed between the impeller and a diffuser and in communication with one of the intake and the outlet. A method in accordance to an example includes pumping a fluid through an electric submersible pump (ESP) that is disposed in a wellbore and reducing a thrust load acting on the impeller in response to recirculating a portion of the pumped fluid through a balance chamber that is formed between one the discharge side or the intake side of the impeller and a diffuser.

[0004] 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 claimed subject matter.

BRIEF DESCRIPTION OF THE DRAWINGS

[0005] The disclosure is best understood from the following detailed description when read with the accompanying figures. It is emphasized that, in accordance with standard practice in the industry, various features are not drawn to scale. In fact, the dimensions of various features may be arbitrarily increased or reduced for clarity of discussion.

[0006] Figure 1 is a schematic view of an electric submersible pump (ESP) system according to one or more aspects of the disclosure deployed in a wellbore.

[0007] Figure 2 is a partial sectional view of a prior art radial flow type pump stage utilizing a conventional balance chamber with a balance ring extending from the impeller.

[0008] Figure 3 is a partial sectional view of a radial or mixed flow style pump stage incorporating an inverted balance ring in accordance to one or more aspects of the disclosure.

[0009] Figures 4 and 5 are partial sectional views of radial or mixed flow style pump stages incorporating features to control fluid recirculation across a radial clearance and through a balance chamber in accordance to one or more aspects of the disclosure.

[0010] Figure 6 is a partial sectional view of an axial flow style pump incorporating a balance chamber in accordance to one or more aspects of the disclosure. [0011] Figure 7 is a partial sectional view of an axial flow style pump incorporating an inverted balance chamber in accordance to one or more aspects of the disclosure.

[0012] Figures 8, 9 and 10 are partial sectional views of axial flow style pumps incorporating features to control fluid recirculation across a radial clearance and through a balance chamber in accordance to one or more aspects of the disclosure.

[0013] Figures 11 and 12 are partial sectional views of axial flow style pumps having balance chambers formed between a discharge side of the impeller and a diffuser in accordance to one or more aspects of the disclosure.

[0014] Figures 13 and 14 are partial sectional views illustrating centrifugal pumping features that can be incorporated in axial flow style pumps in accordance to one or more aspects of the disclosure.

DETAILED DESCRIPTION

[0015] It is to be understood that the following disclosure provides many different embodiments, or examples, for implementing different features of various embodiments. Specific examples of components and arrangements are described below to simplify the disclosure. These are, of course, merely examples and are not intended to be limiting. In addition, the disclosure may repeat reference numerals and/or letters in the various examples. This repetition is for the purpose of simplicity and clarity and does not in itself dictate a relationship between the various embodiments and/or configurations discussed.

[0016] As used herein, the terms "connect", "connection", "connected", "in connection with", and "connecting" are used to mean "in direct connection with" or "in connection with via one or more elements"; and the term "set" is used to mean "one element" or "more than one element". Further, the terms "couple", "coupling", "coupled", "coupled together", and "coupled with" are used to mean "directly coupled together" or "coupled together via one or more elements". As used herein, the terms "up" and "down"; "upper" and "lower"; "top" and "bottom"; and other like terms indicating relative positions to a given point or element are utilized to more clearly describe some elements. Commonly, these terms relate to a reference point as the surface from which drilling operations are initiated as being the top point and the total depth being the lowest point, wherein the well (e.g., wellbore, borehole) is vertical, horizontal or slanted relative to the surface. For the purpose of clarity, an arrow 10 is included in the Figures to indicate the direction of upthrust and an arrow 12 indicates the direction of downthrust.

[0017] Figure 1 illustrates an electrical submersible pump system 20 deployed in a well 28. Submersible pumping system 20 may comprise a variety of components depending on the particular application or environment in which it is used. The illustrated pumping system 20 includes a pump 22 coupled to an electric motor 24 and a motor protector 26. Pump 22 may include two or more stages 100, e.g., compression stages. The pump stages are characterized by the angle of flow passages in the impellers. The stages may be radial flow, mixed flow, or axial flow. The net thrust load, e.g. downthrust load, resulting from rotation of the impellers may be resisted by a bearing 27 illustrated in Figure 1 in motor protector 26.

[0018] Well 28 includes a wellbore 32 drilled into a geological formation 30 containing for example a desirable production fluid 150, such as petroleum. Wellbore 32 may be lined with a tubular casing 34. Perforations 36 are formed through wellbore casing 34 to enable flow of fluids between the surrounding formation 30 and the wellbore 32. Submersible pumping system 20 is deployed in wellbore 32 by a deployment system 38 that may have a variety of configurations. For example, deployment system 38 may comprise tubing 40, such as coiled tubing or production tubing, connected to submersible pump 22 by a connector 42. Power may be provided to the submersible motor 24 via a power cable 44. The submersible motor 24, in turn, powers submersible pump 22 which can be used to draw in production fluid 150 through a pump intake 46. Within submersible pump 22, a plurality of impellers 102 (Figures 3-14) are rotated to pump or produce the production fluid 150 through, for example, tubing 40 to a desired collection location which may be at a surface 48 of the Earth.

[0019] With reference generally to Figures 1-14, ESP stages 100 are characterized by the angle of the flow passageways 112 in the impellers 102. With excessive GVF (gas volume fraction) a pump stage can gas-lock, meaning that it does not produce sufficient head to continue producing stable flow. The GVF capability of a stage is related to the flow angle. In radial flow stages, the impeller flow passageways 112 are radial. These have the lowest gas capacity because the gas tends to centrifugally separate from the liquid and build up in the radial flow passage rather than pass through. Mixed flow stages can handle higher GVF because the flow angle is somewhere between radial and axial, e.g. at an angle of 45 degree relative to the shaft 104. Figures 3-5 illustrate radial or mixed flow stages in accordance to one or more aspects of the disclosure. Axial flow stages 100 can handle the highest GVF because they do not centrifugally separate the gas in the fluid 150. The impeller 102 in an axial flow stage is similar to a screw that pushes along all fluid and gas axially. Axial flow stages 100 in accordance to one or more aspects of the disclosure are illustrated in Figures 6-14. [0020] The head produced by an impeller 102 results in a higher pressure on the discharge, or upper, side 122 of the impeller 102 than on the intake, or lower, side 125 of the impeller 102. This produces a downward thrust 12, known as downthrust. The cumulative downthrust of all the stages 100 can add up to a very high force, which may be carried by a thrust bearing 27 in the motor protector 26 for example. The capacity of the thrust bearing 27 can be a limiting factor in ESP design. Because downthrust 12 is transmitted to the thrust bearing 27 through a shaft, the shaft is subject to axial deflection. Mechanical shaft seals on the protector shaft are adversely affected by excessive shaft deflection due to high downthrust loads 12, which affects the life of the ESP.

[0021] In radial and mixed flow stages 100, the downthrust 12 may be reduced by a balance chamber 120 between the upper or discharge side of the impeller and the lower side 124 of the diffuser 118. Through controlled recirculation (see, e.g. Figures 3-5), the pressure in the balance chamber 120 above the impeller 102 is reduced to nearer the pressure below the impeller, e.g. at intake 110, thus reducing downthrust. The balance chamber 120 is typically sealed from the discharge pressure by a seal created by a small running clearance 127 between a cylindrical balance ring 134 projecting from one of the upper side 122 of the impeller and the lower side 124 of the diffuser 118 and an inner surface 138 of a cylindrical balance bore 132 formed in the other of the upper side of the impeller and the lower side of the diffuser. This running clearance 127 permits leakage of some fluid 150 from the impeller outletl l4 into the balance chamber 120, which tends to raise the pressure in the balance chamber 120. However, pressure build-up in the balance chamber is limited by recirculation of the leakage through recirculation holes 128 that lead from the balance chamber to the intake of the impeller. These holes are sized to regulate the pressure in the balance chamber and thus regulate the downthrust 12.

[0022] The pressure on the upper side of an ESP impeller in an axial pump may be further reduced by addition of centrifugal pumping features such as vanes 156 and grooves or radial holes 154 to the upper side of the impeller or other rotor. The centrifugal pumping action reduces downthrust 12 by reducing the average pressure on the upper side of the impeller. When used with a balance chamber, the pumping feature produces a back pressure at the balance ring that reduces the recirculation leakage past the balance ring. At the same time it reduces the pressure on the inner portion of the balance chamber. The net result is a greater balance effect for a lower loss of flow to recirculation.

[0023] The net force on an impeller is the sum of thrust forces in both the upward 10 and downward 12 directions. A higher pressure on a discharge side of an impeller contributes to a downthrust 12, while momentum of fluid flow entering the impeller from below and a change of direction of fluid flow from an axial direction to a radial direction imparts an upthrust 10 component on the impeller. In submersible pumping systems containing multiple pumping stages, the net downthrust 12 loads can become large. Generally, operating near best efficiency point (BEP) and at operating points of lower flow rate and higher head, the downthrust component dominates, producing a net downthrust. However, at operating points of very high flow and low head, the upthrust component can dominate, producing a net upthrust on the impeller. This moves the impeller up against the diffuser above it. Unless the pump shafts are locked to the protector shafts by cross pins or other means, all of which are cumbersome, this upthrust must be carried by relatively low capacity thrust washers in the stages rather than by the high capacity thrust bearing in the protector. The limited upthrust capacity of the thrust washers can limit the maximum safe flow rate of the pump.

[0024] Refer now to Figure 2 illustrating a partial sectional view of a stage 50 of a prior art submersible pump 52. Pump 52 includes an impeller housing or impeller 102 coupled to a shaft 104 that rotates about a central axis 106. Shaft 104 is rotated by the pumping system motor causing impeller 102 to rotate within an outer pump housing 108. Each impeller draws fluid 150 in through an impeller or stage intake 110 of an impeller passageway 112 and discharges the fluid through an impeller outlet 1 14. The fluid 150 may be discharged from the impeller outlet 114 into a diffuser passageway 116 formed by a diffuser housing or diffuser 118. The fluid may then flow into the impeller intake 110 of the next stage of the pump.

[0025] The prior art pump stage 50 includes a conventional balance chamber 54 defined in part by cylindrical balance ring 134 that extends upward from the upper side 122 of the impeller 102 into a balance bore 132 formed in the lower side 124 of the diffuser 1 18. The balance ring 134 overlaps a portion of the balance bore 132 such that a seal is provided by a radial running clearance 127 between an inner surface 138 of the balance bore 132 and an outer surface 140 of the balance ring 134. A balance passageway 126 including the radial running clearance 127 is provided between the balance chamber 54 and the impeller intake 114. Leakage of fluid 150 may occur across the radial running clearance 127 from the high pressure impeller discharge 114 into the convention balance chamber 54. A recirculation hole 128 is in fluid communication between the conventional balance chamber 54 and the impeller intake 110. The recirculation hole 128 is illustrated formed axially through a hub portion 130 of the impeller 102.

[0026] In operation of a prior art pump stage 50 having a conventional balance chamber 54, some fluid 150 leaks from the impeller passageway 112 proximate the impeller discharge 1 14 across the radial running clearance 127 into the conventional balance chamber 54. Recirculation hole 128 permits fluid communication between the conventional balance chamber 54 and the impeller intake 1 10 to equalize the pressure within the balance chamber 54 and the impeller intake 110. As a result, the pressure within the balance chamber 54 is less than the pressure at the impeller outlet 114 reducing the net downthrust 12 on the impeller 102.

[0027] Figures 3-5 illustrate radial flow or mixed flow style electrical submersible pumps in accordance to aspects of the disclosure. Figures 6-14 illustrated axial flow style electrical submersible pumps. For purposes of clarity the reference numbers are not repeated on each of the figures. Accordingly, description of a particular figure is made with reference generally to the other figures.

[0028] Refer now to Figure 3, illustrating a partial sectional view of a portion of a radial or mixed flow stage 100 of an electrical submersible pump 22 in accordance to one or more aspects of the disclosure. The illustrated stage 100 includes an inverted balance chamber 120 formed between the upper or discharge side 122 of the impeller 102 and a lower side 124 of diffuser 118.

[0029] Inverted balance chamber 120 is formed by a balance ring 134 extending downward from the diffuser into a balance bore 132 formed by the upper side 122 of the impeller housing or impeller 102. The balance ring 134 overlaps a portion of the balance bore 132 such that a radial running clearance 127 between an inner surface 138 of the cylindrical bore 132 and an outer surface 140 of the balance ring 134 seals. The inverted balance chamber is in fluid communication with the impeller outlet 1 14 through a balance passageway 126 across the running clearance 127. In the inverted balance chamber 120 configuration, the balance passageway 126 and radial clearance 127 are oriented such that leaking fluid 150 is directed across running clearance 127 and toward the recirculation hole 128. Recirculation or balance hole 128 is illustrated extending between the balance chamber 120 and the impeller intake 110.

[0030] In operation of a submersible pump 22 that includes a stage 100 as illustrated in Figure 3, some fluid 150 leaks from the impeller outlet 114 across the radial running clearance 127 between the balance bore 132 and the balance ring 134 and into the balance chamber 120. The recirculation hole 128 communicates fluid 150 between the impeller intake 110 and the balance chamber 120 and acts to substantially equalize the pressure within the balance chamber 120 with an intake pressure of the impeller intake 110. By inverting the balance chamber 120, the balance passageway 126 and the radial clearance 127 generally direct the flow of fluid 150 passing therethrough toward the recirculation hole 128. Directing the fluid 150 toward the recirculation hole 128 results in less loss of fluid velocity and less increase in pressure in the balance chamber 120. As a result, the pressure within the balance chamber 120 is less than the outlet pressure at the impeller outlet 114. Therefore, the balance chamber 120 counteracts a portion of the net downthrust 12 at each impeller 102. In a stack including more than one stage 100, a cumulative reduction in downthrust can be achieved.

[0031] Figure 4 is a partial sectional view of a portion of a radial or mixed flow stage 100 of an electric submersible pump 22 in accordance to one or more aspects of the disclosure. Stage 100 illustrated in Figure 4 includes a feature, generally denoted by the numeral 136, disposed at the radial clearance 127 to change the size of the radial clearance 127 between in the inner surface 138 of the balance bore 132 and the outer surface 140 of the balance ring 134 based on the axial spacing of the impeller and the diffuser relative to one another. In the configuration illustrated in Figure 4, feature 136 includes a raised or recessed surface, e.g. a stepped surface formed on at least one of the inner surface 138 or the outer surface 140. In the illustrated stage 100, a stepped surface 139 is formed on a portion of the inner surface 138 and a stepped surface 141 is formed on the outer surface 140. In Figure 4 the balance chamber is illustrated as conventional balance chamber with the balance ring 134 extending from the upper side 122 of the impeller 102 into the balance bore 132 formed in the lower side 124 of the diffuser 118. In this configuration, the balance chamber acts as an upthrust snubber. The balance chamber 120 may be configured as an inverted chamber with the balance ring 134 extending from the diffuser 118 into the balance bore 132 formed by the upper side 122 of the impeller 102. When the feature 136 increases the size of the radial clearance 127 the recirculation flow of fluid 150 into the balance chamber 120 is increased, which increases the pressure in the balance chamber 120 and increases the downthrust 12. When the size of the radial clearance 127 between the balance bore 132 and the balance ring 134 is minimized, the recirculation flow of fluid 150 into the balance chamber is minimized, which reduces the pressure in the balance chamber 120 and reduces the downthrust 12 acting on the impeller 102 and the net downthrust on the shaft 104.

[0032] During operation of a submersible pump 22 that includes a stage 100 in accordance with aspects of Figure 4, conditions may be present that result in net downthrust 12 or net upthrust 10 being exerted on the submersible pumping system 20. The cumulative effect of downthrust 12 or upthrust 10 created by each stage 100 can result in vertical deflection of components within the submersible pumping system 20. For example, large downthrust loads may displace the impeller 102 downward relative to the diffuser 118. This displacement results in a greater overlap between the stepped surface 139 and the stepped surface 141 illustrated in Figure 4. As the overlap between the stepped surface 139 and the stepped surface 141 increases, the ease with which fluid 150 can flow through the balance passageway 126 and radial clearance 127 between the stepped surface 139 and the stepped surface 141 decreases. As the flow of fluid 150 into the balance chamber 120 decreases, the pressure within the balance chamber 120 is more closely maintained to the pressure at the impeller intake 110. Because the pressure within the balance chamber 120 is less than the pressure at the impeller outlet 1 14, the net downthrust upon the impeller 102 is reduced. [0033] During conditions when a net upthrust exists, the impeller 102 may be displaced toward the diffuser 118 if the upthrust force is sufficient to overcome downthrust, gravitational, and frictional forces acting upon the impeller 102. When sufficient upthrust exists to displace the impeller 102 toward diffuser 1 18, the overlap between the stepped surface 139 and the stepped surface 141 decreases. As the overlap decreases the radial clearance 127 increases and it becomes easier for fluid 150 to flow into the balance chamber 120. The increased flow of fluid 150 into balance chamber 120 minimizes the balancing effect of the balance chamber 120, as the balance chamber pressure increases relative to the impeller intake 110 pressure, creating a downthrust 12 load on the impeller housing 102 reduces the net upthrust. Reduction of upthrust at each stage 100 has a cumulative effect upon the net upthrust upon the submersible pumping system 20.

[0034] Figure 5 is a partial sectional illustration of a stage 100 of a submersible pump 22 in accordance to one or more aspects of the disclosure. Stage 100 illustrated in Figure 5 includes a feature, generally denoted by the numeral 136, disposed at the radial clearance 127 to change the size of the radial clearance 127 between in the inner surface 138 of the balance bore 132 and the outer surface 140 of the balance ring 134 based on the axial spacing of the impeller and the diffuser relative to one another. In the configuration illustrated in Figure 5, feature 136 includes a tapered inner surface 138 and/or outer surface 140. For example, with reference to Figures 2 and 3 the outer surface 140 of the balance ring and the inner surface 138 of the bore 132 are substantially parallel to the shaft 104 and the axis of rotation 106. In the configuration of Figure 5, at least one of the inner surface 138 and the outer surface 140 are tapered so as to extend at an angle that is not parallel with the shaft 104 and the axis of rotation. For example, if the axis of rotation 106 were oriented vertically, the plane of the inner surface 138 and/or the outer surface 140 would be oriented at an angle offset from vertical.

[0035] The outer surface 140 of the balance ring 134 extends from a first end 142 to a second end 144. When the outer surface 140 is tapered the radial distance between the first end 142 and the shaft 104 and the axis of rotation 106 is different from the radial distance between the second end 144 of the outer surface 140 the shaft 104 and axis of rotation. Similarly, the inner surface surface 138 is tapered the radial distance between the first end 146 and the shaft 104 is different from the radial distance between the second end 148 and the shaft 104. Figure 5 illustrates a non- limiting example, with the inner surface 138 and the outer surface 140 tapered. In this example, the outer surface 140 tapers radially away from the shaft 104 as the surface moves from the first end 142 to the second end 144. In this example, the first end 142 is an interior end of the inner surface 138 and the second end 144 is the outer end of the inner surface. The inner surface 138 tapers from the first end 146 radial toward the shaft 104 as the inner surface extends toward the second end 148. Accordingly, in this illustrated example, as the impeller 102 is moved axially away from the diffuser 1 18, for example in response to a downthrust, the radial clearance 127 between the inner surface 138 and the outer surface 140 is minimized as the second end portions 144 and 148 are urged in contact with one another. Minimizing the size of the radial clearance 127 reduces the recirculation flow through the balance passageway 126 into the balance chamber 120 which reduces the downthrust 12 acting on the impeller 102 in this example. Similarly, in this example if the impeller 102 is moved axially toward the diffuser 118 the radial clearance 127 increases and fluid 150 flow increases from the outlet 114 into balance chamber 120 increasing the pressure in the balance chamber and increasing the downthrust 12 acting on the impeller 102 and thereby reducing the net upthrust.

[0036] Refer now to Figures 6 and 7 illustrating a partial sectional view of a submersible pump 22 in accordance to one or more aspects having axial flow stages 100. Impeller 102 forms an axial impeller flow passageway 112 extending from a stage or impeller intake 110 to in impeller outlet 114. A balance chamber 120, for example a reverse balance chamber, is formed between the intake or lower side 125 of the impeller 102 and an upper side 123 of a diffuser 118, for example the upstream diffuser. A balance or recirculation hole 128 provides fluid communication between the balance chamber 120 and the upper side 122 of the impeller 102 proximate the outlet 1 14. In the illustrated examples the balance or recirculation hole extends axially through a hub portion 130 of the impeller. In this configuration the balance or recirculation holes 128 serve to raise the pressure in the balance chamber 120 and on the intake or lower side 125 of the impeller to substantially the same pressure as at the discharge or outlet side 122 of the impeller, increasing the pressure below the impeller rather than decreasing the pressure above the impeller. The balance passage 126 provides fluid communication, for example through leakage, between the impeller intake 110 and the balance chamber 120 across the radial clearance 127.

[0037] In the Figure 6 configuration the balance ring 134 extends axially downward from the lower side 125 of the impeller 102 into the balance bore 132 formed in the upper side 123 of the diffuser 118. In Figure 7 the balance ring 134 is inverted and extends axially upward from the upper side 123 of the diffuser 118 into the balance bore 132 formed in the lower side 125 of the impeller 102.

[0038] During operation of a submersible pump 22 conditions may be present that result in downthrust 12 or upthrust 10 being exerted on the submersible pumping system 20. In the Figure 6 and 7 examples, when downthrust moves the impeller 102 axial downward toward the diffuser 118 the length of the overlap and engaging section of the inner surface 138 of the bore 132 and the outer surface 140 of the balance ring 134 is maximized thereby minimizing the leakage of fluid 150 across the running clearance 127 from the balance chamber 120 to the lower pressure intake 110. Minimizing the leakage from the balance chamber 120 minimizes the pressure differential between the upper outlet side 122 of the impeller and the lower side 125 of the impeller thereby producing the balancing effect. If on the other hand the operating point produces upthrust 10, moving the impeller 102 away from the upstream diffuser 118 the length of the portion of the inner surface 138 and the outer surface 140 that overlap and engaged to form the radial running clearance 127 is reduced thereby increasing the leakage of fluid 150 from the balance chamber across the running clearance 127 to the impeller intake 110. The increase in the recirculation fluid flow decreases the balancing effect, e.g. increasing the pressure differential between the upper side of the impeller and the lower side of the impeller, thereby shifting the impeller 102 away from upthrust 10.

[0039] Figure 8 is a partial sectional view of an axial flow submersible pump 22 in accordance to one or more aspects of the disclosure. Stage 100 illustrated in Figure 8 includes a feature, generally denoted by the numeral 136, disposed at the radial clearance 127 to change the size of the radial clearance 127 between in the inner surface 138 of the balance bore 132 and the outer surface 140 of the balance ring 134 based on the axial spacing of the impeller 102 and the diffuser 118 relative to one another. In the Figure 8 configuration the feature 136 may include a stepped surface, e.g., raised or recessed, formed on at least one of the inner surface 138 or the outer surface 140 as described for example with reference to the mixed or radial flow submersible pump illustrated in Figure 4. For example, in Figure 8 the outer surface 140 of the balance 134 has a stepped surface 141 which is offset from the same plane as the other portions of the outer surface 140. In this example, the offset portion 141 is located proximate to the outer or second end 144 of balance ring 134. In the Figure 8 example the inner surface 138 also includes a stepped surface 139 which is offset from the same plane as the other portions of inner surface 138. In this example, the stepped surface 139 is located proximate to the outer or second end 148.

[0040] In operation the size of the radial clearance 127 changes with the axial spacing of the impeller 102 from the diffuser 118 at the balance chamber 120. For example, large downthrust 12 loads may displace the impeller 102 axially downward toward the diffuser 118. This displacement increases the length of the overlap between the inner surface 138 with the stepped surface 139 and the stepped surface 141 with the outer surface 140. As the overlap between the balance bore 132 and the balance ring 134 increases, the ease with which fluid 150 can flow through the radial clearance 127 decreases, thus making it more difficult for fluid 150 to flow from the balance chamber 120 through the radial clearance 127 and balance passageway 126 to the impeller intake. As the recirculation flow of fluid 150 into the balance chamber 120 decreases, the pressure within the balance chamber 120 is maintained closer to the pressure at the impeller outlet 1 14 in the Figure 8 configuration. Because the pressure within the balance chamber 120 is greater than the pressure at the impeller intake 110, the balance chamber 120 counteracts a portion of the downthrust acting upon the impeller 102. Reduction of downthrust at each stage 100 has a cumulative effect upon the net downthrust upon the submersible pumping system 20. [0041] During conditions when an upthrust 10 exists, the impeller 102 may be displaced away from the diffuser 1 18. When sufficient upthrust 10 displaces the impeller 102 away from the diffuser 118, the overlap between the inner surface 138 with the stepped surface 139 and the overlap between the outer surface 140 with the stepped surface 141 decreases. As the length of the overlap decreases fluid 150 leakage across the radial clearance 127 increases. In accordance to one or more aspects the size of the radial clearance 127 increases as the length of the overlap decreases. As the recirculation flow of fluid 150 into the balance chamber 120 and through the balance passageway 126 into the impeller intake 110 increases, the pressure within the balance chamber 120 and on the lower side 125 of the impeller 102 relative to the upper side 122 of the impeller 102. Reducing pressure within the balance chamber 120 minimizes the balancing effect of the balance chamber 120 and acts to shift the impeller 102 away from upthrust 10.

[0042] Figure 9 illustrates a partial sectional view of an axial flow submersible pump 22 in accordance to one or more aspects of the disclosure. The pump 22 illustrated in Figure 9 includes a feature, generally denoted by the numeral 136, disposed at the radial clearance 127 to change the size of the radial clearance 127 between in the inner surface 138 of the balance bore 132 and the outer surface 140 of the balance ring 134 based on the axial spacing of the impeller 102 and the diffuser 1 18 relative to one another. In the non-limiting example of Figure 9 the balance chamber 120 is formed between the lower side 125 of the impeller 102 and the upper side 123 of the upstream diffuser 118 as described above with reference to Figure 6. Balance or recirculation holes 128 provide fluid communication between the upper side 122 of the impeller 102 and the balance chamber 120. The recirculation rate of the fluid 150 through the balance chamber is controlled by the leakage or flow of the fluid 150 from the balance chamber 120 through the balance passageway 126 and to the impeller intake.

[0043] Similar to the radial or mixed flow pump 22 described above with reference to Figure 5, the feature 136 includes tapering at least one of the surfaces 138 or 140 such that the surface is not parallel with the shaft 104 and the axis of rotation 106.

[0044] The outer surface 140 of the balance ring 134 extends from a first end 142 to a second end 144. When the outer surface 140 is tapered the radial distance between the first end 142 and the shaft 104 and the axis of rotation 106 is different from the radial distance between the second end 144 of the outer surface 140 the shaft 104 and axis of rotation. Similarly, the inner surface 138 of the balance bore 132 extends from a first end 146 to a second end 148 and when the inner surface 138 is tapered the radial distance between the first end 146 and the shaft is different from the radial distance between the second end 148 and the shaft. Figure 9 illustrates a non-limiting example, with both the inner surface 138 and the outer surface 140 tapered. In this example, the inner surface 138 slopes away from the shaft 104 such that the second end 148 is radially farther from the shaft 104 than the first end 146 is from the shaft 104. The outer surface 140 slopes toward the shaft 104 such that the second end 144 is radially closer to the shaft 104 than the first end 142 is to the shaft 104.

[0045] With reference to Figure 9, a downthrust 12 load may displace the impeller 102 toward diffuser 118 which decreases the radial clearance 127. As the recirculation flow of fluid 150 into through balance chamber 120 decreases, the pressure within the balance chamber 120 is maintained closer to the pressure of the impeller outlet 114. Because the pressure within the balance chamber 120 is greater than the pressure at the impeller intake 110, the balance chamber 120 counteracts a portion of downthrust 12 on the impeller 102.

[0046] During conditions when a net upthrust 10 exists, the impeller 102 may be displaced up and axially away from the diffuser 118 increasing the size of radial clearance 127. As the recirculation flow of fluid 150 through the balance chamber 120 increases, the pressure within the balance chamber 120 is lowered relative to the pressure at the upper side 122 of the impeller 102 which is in communication with the balance chamber 120 through recirculation holes 128. Reducing pressure within the balance chamber 120 minimizes the balancing effect of the balance chamber 120 and acts shift or urge the impeller 102 away from upthrust 10.

[0047] Figure 10 illustrates a partial sectional view of an axial flow submersible pump 22 in accordance to one or more aspects. An axial seal 152 is disposed within the balance bore 132 of the balance chamber 120 to reduce the fluid 150 leakage through the balance passageway 126 in selected conditions. For example, in Figure 10 the impeller 102 is shown axially moved away from the diffuser 118 under an upthrust condition such that the balance ring 134 is not in sealing contact with the axial seal 152. If the pump 22 is in downthrust 12 and the impeller 102 is moved axially toward the diffuser 118, sealing contact between the balance ring 134 and the axial seal 152 is achieved thereby reducing the leakage through the balance passageway 126 and increasing the pressure in the balance chamber to counteract the downthrust 12. If the pump 22 begins to go into upthrust 10 and the impeller 102 moves upward, the axial seal 152 disengages and allows more recirculation leakage, which will reduce the pressure under the impeller and tend to tip the balance from upthrust 10 to downthrust 12 in accordance to some aspects.

[0048] Figure 1 1 illustrates a partial sectional view of an axial flow pump 22 having a balance chamber formed between the upper or discharge side 122 of the impeller 102 and the lower side 124 of the downstream diffuser 118 in a similar manner to the radial or mixed flow pump 22 described with reference to Figure 3.

[0049] Figure 12 is a partial sectional view of an axial flow submersible pump 22 having a conventional balance chamber 120. Each stage 100 comprises the impeller 102 coupled to the shaft 104 that is rotatable about the central axis 106. Rotation of the shaft 104 by submersible motor 24 causes the impeller 102 to rotate within an outer pump housing 108. Each impeller 102 draws the fluid 150 in through the impeller intake 110 and routes the fluid 150 along the interior impeller passageway 112 before discharging the fluid 150 through the impeller outlet 114 and into the axially adjacent diffuser passageway 116 of the diffuser 1 18. The interior passageway 112 is defined by the shape of the impeller 102. The diffuser passageway 116 is defined by the shape of the diffuser 118.

[0050] In accordance to some embodiments, each stage 100 includes a balance chamber 120 formed between the upper side 122 of the impeller 102 and the lower side 124 of the diffuser 118. The balance chamber 120 is in fluid communication with the impeller intake 110 via a balance or recirculation hole 128 and is in fluid communication with the impeller outlet 114 via the balance passageway 126. The recirculation hole 128 is formed in the hub portion 130 of the impeller 102 and extends axially from the balance chamber 120 to the lower side 125 of the impeller proximate the impeller intake 110. Fluid 150 flow through the balance passageway 126 is restricted by the radial running clearance 127 between the inner surface 138 and the outer surface 140.

[0051] Operation of a submersible pump 22 that includes an axial flow stage 100 is now described with reference to Figure 12. Some fluid 150 passes through the radial clearance 127 between the balance bore 132 and the balance ring 134 from the impeller outlet 114 into the balance chamber 120. The recirculation hole 128 permits fluid 150 communication between the impeller intake 1 10 and the balance chamber 120 and acts to substantially equalize the pressure within the balance chamber 120 with a pressure at the impeller intake 110. As a result, the pressure within the balance chamber 120 is less than the pressure at the impeller outlet 114. Because the pressure within the balance chamber 120 is less than the pressure at the impeller outlet 1 14, a portion of the downthrust 12 on the impeller 102 is counteracted.

[0052] A centrifugal pumping feature may be added to the upper side of an impeller or other rotor of an axial flow pump 22 to reduce the average pressure on the upper side of the impeller and thereby reduce the downthrust 12 produced by an axial flow stage 100 as shown for example in Figures 6-12. The centrifugal feature may be a negative feature 154, see e.g. Figure 13, such as a groove or radial hole formed in the upper element or a positive feature 156, see e.g. Figure 14, such as a vane that is added to the element. The pumping feature 154, 156 may provide a greater reduction in downthrust for less loss of fluid flow through recirculation.

[0053] Figure 13 is a partial sectional view of an axial flow submersible pump 22 in accordance illustrating a negative centrifugal pumping feature 154 to one or more aspects of the disclosure. In the illustrated example, the negative centrifugal feature is a radial hole 154 that provides radial fluid communication between the impeller outlet 114 and the balance chamber 120 located between the upper side 122 of the impeller 102 and the lower side 124 of the stage diffuser 118. Pump 22 and stage 100 may include balance or recirculation holes 128 as illustrated for example in Figures 11 and 12. The negative pumping feature 154 can be added the axial flow pumps illustrated by way of example in Figures 6-12. [0054] During operation downthrust 12 displaces the impeller 102 down and away from the stage diffuser 118. As the impeller 102 is displaced axially downward and away from the diffuser 118. This axial displacement of the impeller 102 relative to the diffuser 118 results in a reduced overlap length of the running clearance 127 between the inner surface 138 and the outer cylindrical surface 140. As the length of the running clearance 127 decreases, the ease with which fluid 150 can flow through the radial clearance 127 increases, thus increasing the recirculation flow through the balance chamber 120. As the impeller 102 rotates, the centrifugal balance feature 154 acts to reduce pressure within the balance chamber 120 and thereby counteract the downthrust 12 load. This reduction in pressure occurs because of the inertia of the fluid 150 within the centrifugal pumping feature 154. Because the pressure at the impeller outlet 114 is greater than the reduced pressure within the balance chamber 120, the downthrust acting upon the impeller housing 102 is reduced.

[0055] Figure 14 is a partial sectional view of a portion of an axial flow submersible pump 22 in accordance to aspects of the disclosure. Figure 14 illustrates a positive centrifugal pumping feature in the form of a vane 156 located on the upper side 122 of the impeller 102. During operation, the centrifugal vane 156 imparts centrifugal rotation to the fluid 150 that reduces the pressure at the upper side 122 of the impeller 102, for example at the balance chamber 120, relative to the impeller outlet thereby reducing the downthrust 12 on the impeller 102. The positive pumping feature 154 can be added to the axial flow pumps illustrated by way of example in Figures 6-12.

[0056] The foregoing outlines features of several embodiments so that those skilled in the art may better understand the aspects of the disclosure. Those skilled in the art should appreciate that they may readily use the disclosure as a basis for designing or modifying other processes and structures for carrying out the same purposes and/or achieving the same advantages of the embodiments introduced herein. Those skilled in the art should also realize that such equivalent constructions do not depart from the spirit and scope of the disclosure, and that they may make various changes, substitutions and alterations herein without departing from the spirit and scope of the disclosure. The scope of the invention should be determined only by the language of the claims that follow. The term "comprising" within the claims is intended to mean "including at least" such that the recited listing of elements in a claim are an open group. The terms "a," "an" and other singular terms are intended to include the plural forms thereof unless specifically excluded.