Abstract:
A method and apparatus for stabilizing a thrust chamber and circulating fluids within a motor seal is described herein. The apparatus includes a thrust chamber having a thrust runner and a radial bearing. A flow path exists through the radial bearing which stabilizes the thrust runner and circulates fluids in the thrust chamber. The flow path may consist of a plurality of grooves located adjacent to the radial bearing.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    Embodiments described herein generally relate to a thrust chamber for use in a wellbore. More particularly, embodiments described herein relate to a thrust chamber having a flow path configured to circulate lubricating fluids in a motor seal and stabilize a thrust runner. 
         [0003]    2. Description of the Related Art 
         [0004]    To obtain hydrocarbon fluids from an earth formation, a wellbore is drilled into the earth to intersect an area of interest within a formation. The wellbore may then be “completed” by inserting casing within the wellbore and setting the casing therein using cement. In the alternative, the wellbore may remain uncased (an “open hole wellbore”), or may become only partially cased. Regardless of the form of the wellbore, production tubing is typically run into the wellbore primarily to convey production fluid (e.g., hydrocarbon fluid, which may also include water) from the area of interest within the wellbore to the surface of the wellbore. 
         [0005]    Often, pressure within the wellbore is insufficient to cause the production fluid to naturally rise through the production tubing to the surface of the wellbore. Thus, to carry the production fluid from the area of interest within the wellbore to the surface of the wellbore, artificial-lift means is sometimes necessary. The most prominent artificial-lift means are the use of down hole pumps and gas lift. 
         [0006]    Some artificially-lifted wells are equipped with electric submersible pumps. These pumps include electric motors which are submersible in the wellbore fluids. The electric motor connects to a motor seal which connects to a pump. The motor seal functions to seal the motor from the wellbore fluids while allowing the motor to transfer torque to the pump. A motor seal typically includes a thrust protection portion. A thrust protection portion prevents downward thrust and forces created by the pump from damaging the motor. Further, a thrust protection portion prevents up-thrust created by the motor during start-up from damaging the pump or motor seal. 
         [0007]    A thrust protection portion typically includes: a housing for containing two bearing portions, a thrust block, and a lubricating fluid. The thrust block is typically located between each of the bearing portions. The thrust block absorbs the downward forces created by the pump and the upward forces created by the motor during operation of the pump. The bearing portions prevent the thrust block from moving axially relative to the pump assembly while resisting the upward and downward forces. 
         [0008]    The lubricating fluid in the housing is a fixed amount of fluid that circulates in the housing. The lubricating fluid lubricates the thrust block during operation of the pump assembly. During operation, the lubricating fluid absorbs energy from the thrust block and bearing portions, which causes the lubricating fluid to heat up and lose its ability to lubricate over the life of the pumping assembly. 
         [0009]    Circulation of the lubricating fluid occurs in a large gap between the thrust block and the housing. This circulation creates turbulence near the bearing portions. The turbulence creates uneven load patterns on the bearing portion and thrust block. The uneven load patterns results in enhanced wear and vibration of the bearing portion and the thrust blocks. 
         [0010]    Therefore, a need exists for a thrust chamber with the ability to circulate fluids into and/or out of the chamber. There is a further need for a thrust chamber configured to reduce unbalanced forces while circulating fluids. 
       SUMMARY OF THE INVENTION 
       [0011]    The embodiments described herein relate to an apparatus for sealing and protecting a motor for use in a wellbore. The apparatus includes a housing, a thrust runner and a radial bearing. The thrust runner is configured configured to fit inside the substantially cylindrical housing. The radial bearing is located between the thrust runner and the housing. A flow path is created past the thrust runner by one or more grooves between the housing and the thrust runner, wherein the one or more grooves allow a fluid to flow past the radial bearing. 
     
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0012]    So that the manner in which the above recited features of the present invention can be understood in detail, a more particular description of the invention, briefly summarized above, may be had by reference to embodiments, some of which are illustrated in the appended drawings. It is to be noted, however, that the appended drawings illustrate only typical embodiments of this invention and are therefore not to be considered limiting of its scope, for the invention may admit to other equally effective embodiments. 
           [0013]      FIG. 1  is a schematic view of a wellbore according to one embodiment described herein. 
           [0014]      FIG. 2  is a cross-sectional view of a motor seal according to one embodiment described herein. 
           [0015]      FIG. 3  is a cross-sectional view of a thrust chamber according to one embodiment described herein. 
           [0016]      FIGS. 4A and 4B  are a cross-sectional view of a thrust housing according to one embodiment described herein. 
           [0017]      FIG. 5A  is a top view of a thrust runner according to one embodiment described herein. 
           [0018]      FIG. 5B  is a cross-sectional view of a thrust runner according to one embodiment described herein. 
           [0019]      FIG. 6A  is a perspective view of a bearing portion according to one embodiment described herein. 
           [0020]      FIG. 6B  is a side view of a bearing portion according to one embodiment described herein. 
           [0021]      FIG. 6C  is a top view of a bearing portion according to one embodiment described herein. 
       
    
    
     DETAILED DESCRIPTION 
       [0022]      FIG. 1  is a schematic view of a wellbore  100  according to one embodiment described herein. The wellbore  100  includes a tubular  102  which is secured in the wellbore  100  using cement, not shown. The wellbore  100  and the tubular  102  intersects at least one production zone  104 . The tubular  102  is typically a string of casing and/or liner; however, it could be any tubular used in downhole operations. Further, the wellbore  100  may be an open hole wellbore. As shown, a conveyance  106  is within the tubular  102  and coupled to an artificial lift assembly  108 . As shown, the conveyance is production tubing; however, it should be appreciated that the conveyance could be any conveyance for delivering the artificial lift assembly  108  into the wellbore  100  for example: a wire line, a slick line, a coiled tubing, a co-rod, a drill string, a casing, etc. The artificial lift assembly  108  pushes the production fluids from the wellbore to the surface of the wellbore  100 . 
         [0023]    The artificial lift assembly  108  includes: a motor  110 , a motor seal  112 , an intake  114 , and a pump  116 . The motor  110 , as shown, is an electric motor; however, it is contemplated that any motor for use in a wellbore may be used. The motor seal  112  includes a thrust chamber which includes one or more flow paths adapted to circulate a lubricating fluid, not shown, from a seal portion of the motor seal to the thrust chamber, and optionally into the motor  110 . The motor seal  112  prevents thrust loads from affecting the motor  110  and/or the pump  116  while allowing torque to transfer from the motor  1   10  to the pump  1   16 . The motor seal  112  equalizes the pressure in the artificial lift assembly  108  with the wellbore fluids and lubricates the thrust chamber as will be discussed in more detail below. The pump  116  is a multistage centrifugal pump; however, it is contemplated that any downhole pump may be used. The intake  114  provides a flow path from the wellbore to the interior of the artificial lift assembly  108 . The intake  114  may be any intake used in downhole operations. It is contemplated that the parts of the artificial lift assembly  108  be arranged in any order so long as the wellbore fluids are pushed to the surface by the pump  116 . 
         [0024]      FIG. 2  shows a cross-sectional view of the motor seal  112  of the artificial lift assembly  108  according to one embodiment of the present invention. The motor seal  112  includes three seal portions  200 ,  202 , and  204  in series coupled to the thrust chamber  206 . Although shown as having three seal portions  200 , any number of seal portions may be used including one. A shaft  208  runs through the seal portions  200 ,  202 , and  204  and the thrust chamber  206 . The motor seal  112  includes a first connector end  210  and a second connector end  212 . As shown the first connector end  210  couples to the motor  110 , and the second connector end  212  couples to the intake  114  and/or the pump  116 , as shown in  FIG. 1 . The motor  110  includes a motor drive shaft, not shown, which couples to the shaft  208  near the first connector end  210  of the motor seal  112 . The pump  116  includes a pump drive shaft, not shown, which couples to the shaft  208  near the second connector end  212  of the motor seal  112 . The connection between at least one of the motor shaft or the pump shaft and the shaft  208  may include an axial slip, not shown, which allows the shaft  208  to move at least partially in the axial direction, such as a splined connection while the motor  110  transfers torque to the shaft  208 . The shaft  208  transfers torque from the motor shaft to the pump shaft. The pump shaft operates the pump in order to push the wellbore fluids to the surface of the wellbore  100 . 
         [0025]    The seal portions  200 ,  202 , and  204 , as shown, are a labyrinth type motor seal. Each of the seal portions  200 ,  202 , and  204  include a chamber  214 , a mechanical seal  216  and a series of ports  218 . The series of ports  218  are in fluid communication with the thrust chamber  206 , as will be discussed in more detail below. Prior to being placed in the wellbore, the motor seal  112  is filled with a lubricating fluid, not shown. The lubricating fluid, in one embodiment, is a dielectric fluid having a specific gravity lower than typical wellbore fluids. Further, any lubricating fluid may be used. 
         [0026]    The thrust chamber  206  includes a thrust housing  219 , a thrust runner  220 , an up-thrust bearing  222 , and a down thrust bearing  224 . The thrust runner  220  couples to the shaft  208  in a manner that allows it to rotate with the shaft  208 , while preventing relative axial movement between the shaft  208  and the thrust runner  220 . The up-thrust bearing  222  and a down thrust bearing  224  are fixed relative to the thrust housing  219 . The up-thrust bearing  222  and the down thrust bearing  224  prevent axial force in the shaft  208  from transferring to the motor  110  or the pump  116  during operation. Between the thrust housing  219  and the thrust runner  220  is a radial bearing  226 . The radial bearing  226  is a fluid bearing which prevents the thrust runner  220  from contacting the thrust housing  219  during operation. The fluid bearing consists of the lubricating fluid which is a relatively non-compressible fluid and is located in a relatively small radial clearance between the thrust housing  219  and the thrust runner  220  in one embodiment. The thrust housing  219  and/or the thrust runner  220  include a flow path through the radial bearing  226 , as will be discussed in more detail below. 
         [0027]      FIG. 3  shows a cross-sectional view of the thrust chamber  206  and the seal portion  204 . The mechanical seal  216  is a typical mechanical seal used in a motor seal. The thrust housing  219 , as shown, couples to the first connector end  210  and the seal portion  204 . Seal rings  300  prevent fluid from leaking into or out of the thrust chamber  206  from the wellbore  100 . The thrust runner  220  couples to the shaft  208  via couplings  302 . The couplings  302  prevent relative axial movement between the thrust runner  220  and the shaft  208 . The upper thrust bearing  222  has one or more load pads  304  and a coupling  306  for coupling the up-thrust bearing  222  to the thrust housing  219 . The coupling  306  prevents the upper thrust bearing  222  from moving in a substantially axial or rotational direction during operation. The downward thrust bearing  224  may be substantially the same as the upper thrust bearing  222 ; therefore, only details of the upper thrust bearing  222  will be discussed in detail. The coupling  306  may be accomplished in any manner for example by bolts, screws, welding, etc. 
         [0028]      FIGS. 4A and 4B  show cross-sectional views of the thrust housing  219 , according to one embodiment of the present invention. The thrust housing  219  includes two or more housing grooves  400  in an inner surface  402  of the housing. The housing grooves  400  may be a portion of the flow path which will be described in more detail below. Two grooves  400  are shown; however, any number of grooves may be provided so long as the grooves  400  are symmetrical around inner surface  402  of the thrust housing  219 . 
         [0029]      FIGS. 5A and 5B  show a top and cross-sectional side view of the thrust runner  220 , respectively. As shown, the thrust runner  220  includes two or more grooves  500  on an outer surface  502  of the thrust runner  220 . In one embodiment, the grooves  500  may be used in conjunction with the housing grooves  400  to form a part of the flow path. Three grooves  500  are shown; however, it should be appreciated that any number of grooves may be provided so long as the grooves  500  are substantially symmetrical around outer surface  502  of the thrust runner  220 . At least one of the sets of grooves  400  or  500  is optional. That is, there may be only grooves  500 , or only housing grooves  400 , or there may be both. The thrust runner  220  may include a profile  504  which corresponds with a matching profile, not shown, on the shaft  208 . The profile  504  transfers torque from the shaft  208  to the thrust runner  220 . 
         [0030]    The housing grooves  400  and the grooves  500  are shown as being substantially parallel with the shaft  208 . This arrangement allows for bi-directional flow of fluids across the thrust runner  220 . The housing grooves  400  and the grooves  500  are also shown as being rectangular grooves in the thrust runner  220  and the thrust housing  219 ; however, it should be appreciated that the grooves may have any geometry so long as the grooves  400  and  500  allow fluids to flow past the thrust runner  220  during operation, such as: rounded, triangular, polygonal, etc. The Fluid flows through the housing grooves  400  and the grooves  500  to stabilize the thrust runner  220  as it rotates in the thrust housing  219 . 
         [0031]      FIGS. 6A-6C  show views of the upper thrust bearing  222 . The upper thrust bearing  222 , as shown, has six load pads  304  symmetrically located around the bearing; however, there could be any number of load pads  304 . The upper thrust bearing  222  includes a bore  600  through which the shaft  208  and lubricating fluid passes. Further, the upper thrust bearing  222  includes a gap  602  between each of the load pads  304  that provide an area for the lubricating fluid to flow during operation. The load pads  304  in operation may have a fluid film, not shown, between the thrust runner  220  and the load pads  304  that aids in reducing friction between the two surfaces. The fluid film is formed from a thin layer of the lubricating fluid on each of the load pads  304 . The fluid film reduces friction between the thrust runner  220  and the load pads  304  during rotation. 
         [0032]    In operation, the wellbore  100  is formed and the formation is perforated. Production fluids then fill the wellbore  100 . To enhance recovery of production fluids to the surface of the wellbore  100 , the artificial lift assembly  108  is run into the wellbore on the conveyance  106 . Before the artificial lift assembly  108  is lowered into the wellbore  100 , the motor seal  112  is filled with the lubricating fluid. The artificial lift assembly  108  is lowered into the wellbore  100  and may be submersed in wellbore fluids. The intake  114  and/or pump  116  allow the wellbore fluids and/or the production fluids to enter the artificial lift assembly  108 . When at a desired location, the motor  110  actuates in order to operate the pump  116 . 
         [0033]    The actuation of the motor  110  turns the motor shaft which transfers torque to the shaft  208 . The torque in the shaft  208  causes the shaft  208  to rotate within the motor seal  112 . The rotation of the shaft  208  is transferred to the thrust runner  220  thereby causing the thrust runner  220  to rotate. The radial bearing  226  substantially prevents the thrust runner  220  from contacting the thrust housing  219  during rotation. The flow path which consists of either the housing grooves  400 , the grooves  500 , or both, circulates the lubricating fluid upon rotation of the thrust runner  220 . The rotation of the thrust runner  220  creates a pressure drop in the flow path across the thrust runner  220  causing the lubricating fluids in the thrust chamber  206  to move toward the pump  116 . Additionally, the lubricating fluid may flow past the thrust runner  220  toward the motor in a space, not shown, between the shaft  208  and the thrust runner  220  which replenishes the lubricating fluid on the motor side of the thrust runner  220 . As the speed of rotation increases the pressure drop across the thrust runner  220  increases thereby increasing the circulation speed. 
         [0034]    Initially the motor  110  and thrust runner  220  begin to rotate and cause shaft  208  and thrust runner  220  to move up toward the pump  116 . The upward movement creates an up-thrust force which is absorbed by the upper thrust bearing  222 . The fluid film between the thrust runner  220  and the upper thrust bearing  222  transfers it to the load pads  304  while reducing friction between the thrust runner and the upper thrust bearing  222 . The load pads  304  transfer the up thrust to the upper thrust bearing  222  which in turn transfers the load to the thrust housing  219 . This prevents the up thrust from transferring up the shaft  208  and into the pump  116 . The circulation of the lubricating fluids past the radial bearing  226  decreases turbulence around the load pads  304 . The decrease in turbulence decreases the vibration and wear on the load pads  304  during operation, thereby enhancing the life of the thrust runner  220  and the upper thrust bearing  222 . 
         [0035]    As the motor  110  continues to turn the shaft  208  and the pump shaft, the pump eventually begins to push wellbore fluids and/or production fluids toward the surface of the wellbore  100 . This pushing/pumping of the fluids toward the surface of the wellbore causes reactive down thrust on the pump shaft and in turn the shaft  208 . The down thrust transfers down the shaft  208  to the thrust runner  220 . The thrust runner  220  transfers the down thrust to the down thrust bearing  224 . The down thrust bearing  224  absorbs the load in the same way as the upper thrust bearing absorbed the up thrust. The circulation of the lubricating fluid reduces the turbulence around the down thrust bearing  224  in the same manner as described above. 
         [0036]    The circulation of the lubricating fluid by the thrust runner causes circulation between the seal portions  200 ,  202 , and  204  and the thrust chamber  206  through the series of ports  218 . The lubricating fluid, which is pushed upward by the rotation of the thrust runner  220 , flows up a first port  250  toward the seal portion  204 . The lubricating fluid enters chamber  214  near the upper end of the chamber  214 . The additional lubricating fluid in the full chamber  214  causes lubricating fluid to flow up the second port  252  and into the chamber  214  of the seal portion  202 . This circulation continues and eventually the lubricating fluid interacts with the wellbore fluids and/or production fluids near the connection between the seal portion  200  and the intake  114  and/or the pump  116 . The interaction between the wellbore fluids and the lubricating fluids causes some wellbore fluids to enter the motor seal  112 . As discussed above, the wellbore fluids may have a higher specific gravity than the lubricating fluids. Thus during circulation, the wellbore fluids will flow toward the bottom of each of the seal portions  200 ,  202 ,  204 . As the wellbore fluids reach the bottom of the first seal portion  200  some of the wellbore fluids will flow down a third port  254  and into the seal portion  202 . The mechanical seals  216  prevent the wellbore fluids from flowing out of the seal portions  200 ,  202 , and  204  along the shaft  208 . The ports  250 ,  252  and  254  are bidirectional, that is fluids can flow up or down the ports  250 ,  252  and  254 . The lubricating fluids will substantially remain in the upper portions of the seal portions  200 ,  202 , and  204 . Because the first port  250  has an entry/exit near the upper portion of the seal portion  204 , wellbore fluids and production fluids are substantially prevented from entering the thrust chamber  206 . The circulation of the lubricating fluids in the seal portions  200 ,  202 , and  204 , with the lubricating fluids in the thrust chamber  206 , increase the cooling of the lubricating fluids in the thrust chamber. That cooling enhances the life of the upper thrust bearing  222  and the down thrust bearing  224 . The flow path in the thrust chamber  206  and the radial bearing allow the artificial lift assembly  108  to operate longer in a wellbore  100  than conventional motor seals. 
         [0037]    In one embodiment, the radial bearing clearance between the thrust housing  219  and the thrust runner  220  is in the range of 0.002 to 0.008 inches. In an alternative embodiment, the radial bearing clearance is less than or equal to 0.008 inches. In yet another alternative embodiment, the radial bearing clearance is greater than or equal to 0.002 inches. The radial bearing effect may be lost if the radial bearing clearance is too large. 
         [0038]    In an alternative embodiment, the motor seal comprises of a bag motor seal rather than the labyrinth motor seal described above. The operation of the thrust chamber  206  is the same as described above; however, the motor seals operate with bags. 
         [0039]    In yet another embodiment, the flow path are in the shape of spiraled grooves, not shown. Thus, the housing grooves  400  or the grooves  500 , or both, have a spiraled configuration. As described above, either housing grooves  400  or grooves  500  are optional. The spiraled flow path decreases the pressure drop across the thrust runner  220 . The spiraled flow pushes the lubricating fluid in one direction past the thrust runner  220 . The spiraled flow may be arranged to push the lubricating fluids toward the pump  116 , thereby creating a circulation as described above. Further, the spiraled flow path may push the lubricating fluids toward the motor  110 . As the lubricating fluids flow toward the motor  110 , they circulate with fluid in the motor  110 . This circulation in the motor  110  increases the life and reliability of the motor  110  during the lifting operation. The circulation between the seal portions  200 ,  202 , and  204  and the thrust chamber  206  remain substantially the same as described above. 
         [0040]    In yet another embodiment, one of the sets of grooves  400  or  500  may be spiraled while the other sets of grooves  400  or  500  is substantially parallel with the shaft  208 . 
         [0041]    While the foregoing is directed to embodiments of the present invention, other and further embodiments of the invention may be devised without departing from the basic scope thereof, and the scope thereof is determined by the claims that follow.