Abstract:
A pump stage is disclosed for use with an electrical submersible pump. The stage includes an impeller and diffuser, each having a hub, blades and an outside ring. In such pump stage, the stage flow area is constructed from separate segments manufactured from wear resistant material. Furthermore, each separate segment is retained by the hub using an external compression fit ring.

Description:
BACKGROUND 
     The proposed invention relates to electrical submersible pumps used for hydrocarbons production from oil wells. Pump construction includes a stack of stages placed inside housing. Each stage includes stationary diffuser and rotating impeller. Abrasive solids are present in the production flow in forms of formation rock or proppant grains. Formation solids average concentration in the production flow is 200 mg/liter. In case of heavy oil production this number can be even much higher. Proppant flow back grains concentration in the production flow can reach concentrations as high as 1 g/liter right after fracturing. Production flow speed inside the pump stage for most applications is around 15 m/sec. This high speed causes the stage geometry erosion wear. Solids being trapped inside the stage small gaps between spinning and stationary components cause the stage material abrasion wear as well. As a result pump efficiency is decreasing. Stages wear also leads to the increase of journal bearings dynamic loads. Accelerated radial bearings wear causes pump premature failure. 
     There are several known technical solutions (analogs) in existence. One of these patents proposes the implementation of iron and boride carbides layers through stage flow area (U.S. Pat. No. 19,830,120). Carbide/boride layers are wear resistant materials. The disadvantage of this technology is surface roughness increase. Consequentially the stage hydraulic characteristics (head and efficiency) are reduced. Diffusion coating technology with wear resistant materials can be used as well. However, due to the limited coating thickness (for diffusion process) eventually it will be worn out with time exposing the base material. 
     The closest technical solution (prototype 1) to the proposed is a turbodrill stage being described in Russian patent Ns 2244090. Turbodrill is a hydraulic machine used for well drilling. Turbodrill construction comprises a stack of axial type stages (rotor plus stator). Stack of rotors is retained on turbodrill shaft and stator stack is retained inside housing. Working fluid circulated from the surface spins the turbodrill shaft with bit attached. According to this patent the turbodrill stage flow area is fabricated from ceramic using the injection molding process. Flow area is retained to metal hub and outside ring through press fit connection. The presented construction of turbodrill stage is wear resistant and maintains good operation characteristics for a long time. Stage disadvantage is the technological complexity of the complete flow area molding from ceramic material. 
     The above mentioned disadvantage has been resolved in the construction of turbodrill stage proposed by Russian company “Techbur” (prototype 2) In this design the stage flow area is constructed of separate ceramic segments. Each segment consists of a blade and attached surface. Special filler (epoxy type glue) is used for segments connection to each other and press fit ring retains all segments around the hub. Filler is used as well for gaps filling between the blades. Separate segments manufacturing is much easier process. Filler erosion wear in blade gaps is this construction disadvantage. As a result the stage operational parameters are going to be reduced once the filler starts wearing out. The goal of the proposed invention is pump stage operational life increase by enhancement of stage abrasion and erosion wear properties. The indicated goal is achieved by constructing the flow area of a submersible pump stage from separate segments manufactured from wear resistant material. Segments are retained in the stage construction through compression fit rings. 
     SUMMARY 
     The following brief summary refers to various embodied features and is no way intended to unduly limit any present or subsequently related claims in this application. 
     An electrical submersible pump stage has impeller and a diffuser. Each impeller and diffuser has a hub, blades and an outside ring. The stage flow area is constructed from separate segments manufactured from wear resistant material. The segments are retained to the hub by external compression fit rings. A sleeve made from plastically deformable materials is installed between the hub and the segments and between the ring and the segments. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  shows a section view of a pump according to the invention; 
         FIG. 2  shows a cross-section on line A-A of  FIG. 1 ; 
         FIG. 3  shows the construction of a pump impeller; 
         FIG. 4  shows the construction of a pump impeller with deformable sleeves; 
         FIG. 5  shows a separate impeller segment design; 
         FIG. 6  shows a side connection between segments; 
         FIG. 7  shows an impeller hub construction with a sealing gasket; 
         FIG. 8  shows a design of an impeller cap; 
         FIG. 9  shows a diffuser construction; 
         FIG. 10  shows a design of a separate diffuser segment; 
         FIG. 11  shows a diffuser design with a deformable sleeve; and 
         FIG. 12  shows a detailed view of part of a pump section. 
     
    
    
     DETAILED DESCRIPTION 
     Electrical Submersible Pump according to the proposed design ( FIG. 1 ) consists off the following main components: housing  1 , shaft  2 , journal bearings  3 , diffusers  4 , compressed inside the housing  1  between head  5  and base  6 . Impellers  7  have been compressed on the shaft  2  by means of a nut  8 . Torque is transmitted from shaft  2  to impeller  7  by means of a rectangular key  9  ( FIG. 2 ). 
     Impeller design is explained in  FIG. 3  and  FIG. 4 . Impeller includes hub  10 , separate segments  11  located around the hub, cap  12  and external ring  13 . Cap  12  and ring  13  connection with segments  11  is press fit. There is a key slot  14  on the hub ID. Segment configuration ( FIG. 5 ) includes blade  15  and adjusting surfaces  16  and  17 . Cylindrical extrusion  18  adjoins surface  16 . Geometry configuration  19  of segment surface  16  is matching the hub configuration  21  through their contact area ( FIG. 3 ). Geometry configuration  20  of segment surface  17  is matching the configuration  22  of cap  12  through the contact area ( FIG. 3 ). Segments  11  are retained in the impeller through compression load from cap  12  and ring  13 . Friction force generated in the connections is sufficient enough for retaining impeller components as one monolithic unit and for torque transmission from the shaft. Segments  11  are being fabricated from wear resistance material with minimum Knoop hardness 500 units. Ceramic and carbides based materials can be used for segment material. 
     Impeller assembly ( FIG. 3 ) is performed in the following way. Segments  11  are being positioned around hub  10 . Ring  13  is heated up to fixed temperature. Heating temperature value is determined based on the compression fit load and depends on the coefficient of ring thermal expansion. Once heated up the ring  13  is placed over extrusions  18  of segments  11  ( FIG. 5 ). Ring  13  is cooling down compressing the segments  11  and squeezing them against hub  10 . At the next step cap  12  is heated up to the fixed temperature and placed over segments. After cooling cap tightly squeezes segments and presses them against hub. In the proposed impeller construction segments retaining is occurring from both ends. This way the construction robustness has been achieved. 
     In order to achieve segments reliable retention and to eliminate chances of some segments being loose due to differences in dimensional tolerances one of the proposed construction versions of the design includes thin sleeves manufactured from deformable material ( FIG. 4 ). First sleeve  23  is installed between segment  11  and cap  12 . Second sleeve  24  is installed between ring  13  and segment  11 . Under squeezing load the sleeves are plastically deformed and load is distributed uniformly through all impeller segments. Copper or material with similar properties can be used for sleeves manufacturing. 
     Labyrinth type face seal  25  ( FIG. 5  and  FIG. 6 ) fabricated at segments sides is another version of the stage construction. The face seal prevents produced fluid contact with hub and cap surfaces. The face seal is constructed in form of a chevron connection between male and female features at segment sides. 
     In order to block fluid recirculation under the segments the certain impeller design version is proposed. Concentric groove  26  ( FIG. 7 ) with adjusting radial slots  27  in quantity equal to the segments quantity is implemented on the hub surface. Elastomer seal  27  is shown in  FIG. 7 . Due to cap  12  heating during impeller assembly the elastomer seal can not be placed in contact area between cap and segment. Soft deformable material can be placed in cap slots  28  ( FIG. 8 ). 
     Diffuser construction is shown in  FIG. 9 . Diffuser consists of hub  29 , segments  30 , external skirt  31  press fit over segments  30  and internal bushing  32 . Bushing  32  is press fit in hub  29 . Diffuser single segment construction geometry is shown in  FIG. 10 . The segment consists of blade  33  and adjusting surfaces  34  and  35 . The contact surface configuration of  35  matches the geometry of the outside surface of hub  29 . The contact surface configuration of  34  matches the configuration of skirt  31  inner surface. Segments  30  and bushing  32  are manufactured from wear resistant material with min Knoop hardness 500. Ceramic or carbide based materials should be used for segments and bushing fabricating. 
     The diffuser assembly is performed in the following order. Bushing  32  is pressed in hub  29 . Segments  30  are positioned around hub  29 . Skirt  31  is heated up to the fixed temperature. Heating temperature value is determined based on the compression fit load and depends on the coefficient of skirt thermal expansion. Skirt  31  is placed over segments  30  ( FIG. 9 ). Cooling down the skirt tightly squeezes segments and presses them against the hub. 
     The chevron type face seal  36  is constructed at the diffuser segment sides ( FIG. 10 ) and prevents hub and skirt surfaces erosion wear. The diffuser face seal configuration is identical to the impeller one, being described above. 
     In order to achieve diffuser segments reliable retention and to eliminate chances of some segments being loose due to differences in dimensional tolerances one of the proposed versions of the design includes thin deformable sleeve  37  placed between segments and skirt ( FIG. 11 ) 
     In order to block fluid recirculation under the diffuser segments a deformable seal can be used. The seal design is identical to impeller seal  27  and placed between hub and segments. 
     A fragment of pumps section with proposed stages is shown in  FIG. 12 . Diffusers  4  stack is compressed inside housing  1 . Impellers  7  with spacers  38  are compressed on shaft  2 . Spacer is fabricated from abrasion resistant material. Ceramic or carbide based materials should be used for spacer manufacturing. Spacer  38  and bushing  32  comprises a pump journal bearing. The proposed pump section design is suited for production of hydrocarbons with high content of abrasive solids. The stage flow area is erosion resistant due to the proper material implementation. Each pump stage has a wear resistant journal bearing to prevent stage abrasion wear.