Abstract:
A method of installing an electrical pump assembly in a subsea wellhead member avoids having to run the pump assembly through the wellhead member after removing the wear bushing. The operator first lowers the pump assembly on a string of tubing at least through the wear bushing while deploying the power cable alongside the tubing. He then connects a retrieval tool to the tubing, inserts the power cable into a slot in a side wall of the retrieval tool, and lowers the retrieval tool. After engaging the wear bushing, the operator retrieves the wear bushing while taking up the power cable. The operator connects a tubing hanger to the tubing, and lowers the pump assembly again until the tubing hanger lands in the wellhead member.

Description:
CROSS REFERENCE TO RELATED APPLICATION  
       [0001]     This application claims priority to provisional application 60/548,359, filed Feb. 26, 2004. 
     
    
     FIELD OF THE INVENTION  
       [0002]     This invention relates in general to installing electrical submersible pumps and in particular to installing an electrical submersible pump in a subsea well.  
       BACKGROUND OF THE INVENTION  
       [0003]     A subsea well of the type concerning herein has a production tree located subsea near the sea floor. The tree lands on a wellhead housing located at the upper end of the well. In one type of well, a tubing hanger lands in the tree, and production tubing suspended from the tubing hanger extends into the well. In another type of well, the tubing hanger lands in the wellhead housing, and the tree is installed on the wellhead housing after running the tubing.  
         [0004]     Both the tree in the first type and the wellhead housing in the second type have bores containing smoothly polished sealing surfaces. Wear bushings are installed in the bores to avoid damage to the sealing surfaces before installing the tubing hanger. The wear bushing provides protection against damage from drill pipe and other tools, and is removed before installing the tubing hanger.  
         [0005]     Many subsea wells produce with natural pressure, but others have insufficient pressure initially or later to flow naturally at adequate rates. Electrical submersible pumps have been installed in surface wells for many years and more recently in subsea wells to pump the well fluid. A typical electrical submersible pump comprises a large electrical motor that secures to the lower end of a centrifugal pump. Normally, the pump assembly is suspended on the production tubing and discharges well fluid into the tubing. A power cable extends from the motor alongside the tubing to the tubing hanger. In the case of a subsea well, the power cable normally terminates at the tubing hanger, and an electrical connection is made between an electrical receptacle on the tubing hanger and a power source on the exterior of the tree.  
         [0006]     The wear bushing in the tree or wellhead housing is normally removed prior to running the submersible pump assembly. This removal allows the tubing hanger to land and seal, but it exposes the seal surfaces to possible damage from the pump assembly as it passes through the tree or wellhead housing.  
       SUMMARY OF THE INVENTION  
       [0007]     In this invention, the operator lowers the pump assembly through the wear bushing in the wellhead member while deploying the power cable alongside the conduit. He then connects a retrieval tool to the conduit, inserts the power cable into a slot in a side wall of the retrieval tool, and lowers the retrieval tool and the pump assembly while deploying power cable until the retrieval tool engages the wear bushing. Then, the operator lifts the conduit and retrieves the wear bushing while taking up the power cable. When the wear bushing reaches the platform, the operator disconnects the retrieval tool from the conduit. The pump assembly will still be below the wellhead member sealing surfaces.  
         [0008]     In the preferred method, the operator then lowers the pump assembly again by adding more conduit until a desired total length of conduit is reached. While doing so, the operator feeds the power cable through the wear bushing, which is preferably supported on a cradle on the platform. The operator then connects a hanger to the conduit, secures the upper end of the cable to the hanger, and lowers the hanger and the conduit until the hanger lands in the wellhead member.  
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0009]      FIG. 1  is a schematic view illustrating a submersible pump being lowered through a Christmas tree containing a wear bushing in accordance with this invention.  
         [0010]      FIG. 2  is a schematic view showing a wear bushing retrieval tool being attached to the upper end of the tubing string after the pump has passed below the tree.  
         [0011]      FIG. 3  is a sectional view of the retrieval tool of  FIG. 2 , taken along the line  3 - 3  of  FIG. 2 .  
         [0012]      FIG. 4  is a sectional view of the wear bushing retrieval tool in engagement with the wear bushing in the tree of  FIG. 1 .  
         [0013]      FIG. 5  is a schematic view of the tree and the wear bushing after the wear bushing has been retrieved to the surface.  
         [0014]      FIG. 6  is a schematic view of a tubing hanger attached to the upper end of the string of tubing after the wear bushing has been retrieved.  
         [0015]      FIG. 7  is a schematic of the tubing hanger of  FIG. 6  being lowered into the tree.  
         [0016]      FIG. 8  is a schematic view showing the tubing string and pump being lowered into the well while the wear bushing is located within the tree.  
         [0017]      FIG. 9  is a schematic view of the tubing string and pump of  FIG. 8  being lowered further, and illustrating the wear bushing retrieval tool in the process of engaging the wear bushing.  
         [0018]      FIG. 10  is a schematic view of the string of tubing and the pump of  FIG. 8  being raised in order to retrieve the wear bushing.  
         [0019]      FIG. 11  is a schematic view of the tubing string and tubing hanger installed in the tree.  
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0020]     Referring to  FIG. 1 , a conventional wellhead assembly is shown located at a sea floor, the wellhead assembly in this drawing comprising a Christmas tree  11 , referred to as a “horizontal” tree, but the invention is applicable to other types of trees also. Tree  11  is located at the upper end of a cased well and has a bore  13  extending through it. A production passage  15  leads laterally outward from bore  13 . Tree  11  also has a tubing annulus bypass passage  17  that leads from a lower portion of bore  13  to an upper portion of bore  13 .  
         [0021]     A bore protector or wear bushing  19  is shown located in bore  13  for protecting the sealing surfaces within bore  13  from damage from tools and equipment being lowered through bore  13 . Wear bushing  19  is a metal sleeve that lands on a shoulder in bore  13  and blocks production passage  15  while located within. Wear bushing  19  is conventional and typically has some type of retainer to selectively retain it within bore  13  against upward movement.  
         [0022]      FIG. 1  shows a string of conduit, preferably production tubing  21 , being lowered into tree  11 . Production tubing  21  may be conventional tubing having individual sections approximately 30 feet in length, each having threaded ends that are secured together. Alternately, tubing  21  could be continuous tubing of a type referred to as “coiled” tubing.  
         [0023]     A conventional electrical submersible pump assembly  23  is schematically shown located at the lower end of tubing  21 . Pump assembly  23  typically comprises a centrifugal pump and an AC three-phase motor. A packer  25  may be located below or above pump  23 . Packer  25  seals to the casing within the well and may be eliminated in some instances. A power cable  27  connects to the motor of pump assembly  23  and extends alongside tubing  21  for supplying power to the motor. Power cable  27  is normally armored cable having three conductors for supplying three-phase AC power. Clamps  29  are secured at selected distances apart from each other alongside tubing  21  to retain power cable  27  with tubing  21 .  
         [0024]     In  FIG. 1 , power cable  27  extends to surface platform  33 , typically a floating platform, where it is deployed from a large reel  31 . In the preferred method, a wear bushing cradle  35  is mounted to platform  33  adjacent opening  36  of platform  33 . Wear bushing cradle  35  is a frame that is fabricated for supporting wear bushing  19  in an inclined position once it is retrieved, as shown in  FIG. 5 . Positions other than inclined are suitable.  
         [0025]     Platform  33  has a derrick with a draw works (not shown) that is employed to support the string of tubing  21  as it is lowered into the well. As tubing  21  is lowered into the well, the operator will feed out power cable  27  from reel  31  and will attach clamps  29  at appropriate points along tubing  21 . The operator will continue the process until pump assembly  23  is below wear bushing  19  in tree  11 . Wear bushing  19  guides pump assembly  23  through tree  11  and prevents pump assembly  23  from damaging sealing surfaces in bore  13 . Wear bushing  19  also protects the sealing surfaces from damage by any other equipment previously lowered through tree  11 .  
         [0026]     Cable clamps  29  may be too large in cross-section to fit through wear bushing  19 . If so, the operator will lower pump assembly  23  below wear bushing  19 , but stop before reaching the first cable clamp  29 . After pump assembly  23  is below tree  11 , the operator attaches a wear bushing retrieval tool  37  to the upper end of the string of tubing  21 , as shown in  FIG. 2 . If the cable clamps  29  were small enough in cross-section to pass through wear bushing  19 , the operator could assemble the entire desired total length of tubing  21  before attaching retrieval tool  37 .  
         [0027]     Wear bushing retrieval tool  37  is a conventional type employed to engage wear bushing  19  to retrieve it from tree  11 . Wear bushing retrieval tool  37  has engaging members that engage slots or a groove in wear bushing  19  ( FIG. 1 ). Wear bushing retrieval tool  37  is modified as illustrated in  FIG. 3  to include an axially extending slot  39  along one side. Slot  39  extends inward from the outer diameter to the inner diameter to receive power cable  27 .  
         [0028]     While the operator could lower wear bushing retrieval tool  37  on tubing  21 , preferably the operator employs drill pipe  41 . Drill pipe  41  is the same type used for drilling, is heavier than tubing  21 , and is made-up and broken out repeatedly many times during the life. Production tubing  21 , on the other hand, is broken out and made up only during certain workover operations. Retrieval tool  37  could be a clamp-type or split-apart tool to facilitate attachment to a tubing string.  
         [0029]     The operator lowers tubing  21  and pump assembly  23  farther into the well on drill pipe  41  until retrieval tool  37  lands in tree  11 , as illustrated in  FIGS. 4 and 9 . In this position, the upper end of production tubing  21  will be located at tree  11  and pump assembly  23  will be located deeper, but not yet at its desired setting depth. As pump assembly  23  is lowered on drill pipe  41 , more power cable  27  is reeled out. Temporary clamps optionally could be used to secure power cable  27  to drill pipe  41  to transfer the weight of power cable  27  to drill pipe  41 . Temporary clamps are not needed if the depth of the water is shallow enough such that the power cable  27  can support its own weight.  
         [0030]     Once retrieval tool  37  has landed in wear bushing  19 , the operator will retrieve it in a conventional manner. Normally this occurs simply by pulling upward with an over pull sufficient to pull loose the retainer (not shown) that retains wear bushing  19  in bore  13  of tree  11 . The operator then begins pulling drill pipe  41  upward back to the surface to retrieve wear bushing retrieval tool  37 . While doing so, the operator rolls power cable  27  back onto reel  31 . If temporary clamps have been used to attach power cable  27  to drill pipe  41 , these clamps will be released as the operator retrieves drill pipe  41 .  
         [0031]     When wear bushing retrieval tool  37  reaches platform  33 , the operator supports the string of tubing  21  with slips and disconnects retrieval tool  37 . In the preferred method, the operator sets wear bushing  19  on cradle  35  with power cable  27  still extending through it as shown in  FIGS. 5 and 10 . Cradle  35  may support wear bushing  19  at an angle with its lower end inclined upward relative to its upper end at about 30 degrees. This position can vary, however, depending on the placement and diameter of reel  31 . The operator then attaches more joints of tubing  21  to lengthen tubing  21  until the total desired length of tubing  21  from tree  11  to the target setting depth has been assembled. During this procedure, as the operator rolls cable  27  out, it passes through wear bushing  19 , which serves as a guide. The operator will also attach additional clamps  29  to tubing  21 .  
         [0032]     When the total length of tubing  21  has been reached, the operator attaches a tubing hanger  43  and supports it in the rig rotary table  45 . The operator cuts power cable  27 , as shown in  FIG. 6 , forms a penetrator termination  49  on the end, and attaches penetrator termination  49  to a receptacle on the lower end of tubing hanger  43 . Once attached, the operator lowers tubing hanger  43  and the string of tubing  21 , as illustrated in  FIG. 7 . Preferably the operator again uses drill pipe  41  to lower the assembly. The operator lands tubing hanger  43  in tree  11 , as illustrated in  FIG. 11 . Electrical power is made up by an electrical connector (not shown) that extends from the assembly of tree  11  into a receptacle provided on tubing hanger  43 . The operator disconnects drill pipe  41  from tubing hanger  43  and retrieves drill pipe  41 .  
         [0033]     Briefly summarizing the operation, first the operator installs wear bushing  19  in tree  11 , as shown in  FIG. 1 . The operator then lowers pump assembly  23  on tubing  21  as shown in  FIG. 8 . Wear bushing  19  protects the sealing surfaces within tree  11  from pump assembly  23  as it is lowered through tree  11 . Once pump assembly  23  is below tree  11 , the operator will retrieve wear bushing  19  on drill pipe  41  as illustrated in  FIG. 9 . Power cable  27  locates within slot  39  ( FIG. 3 ) in the side of retrieval tool  37  as retrieval tool  37  is lowered and engages wear bushing  19 . The operator retrieves wear bushing  19  on drill pipe  41 , rolling cable  27  back on to reel  31  during this process.  
         [0034]     Once retrieved, the operator places wear bushing  19  on cradle  35  ( FIG. 5 ) and makes up the rest of the total desired length of the string of tubing  21 , clamping power cable  27  to tubing  21  during the process. When the total of length of tubing  21  has been made up, the operator cuts cable  27 , attaches penetrator  49  ( FIG. 6 ) to tubing hanger  43  and lowers tubing hanger  43  on drill pipe  41  into engagement with tree  11 . Drill pipe  41  is then retrieved, leaving the completed assembly as shown in  FIG. 11 .  
         [0035]     The invention has significant advantages. The method avoids the possibility of damage to the seal surfaces in the tree while lowering the pump through the tree bore. The wear bushing is retrieved only after the pump is suspended below the tree bore. The use of a cradle allows the operator to deploy power cable through the wear bushing after it has been retrieved.  
         [0036]     While the invention has been shown in only one of its forms, it should be apparent to those skilled in the art that it is not so limited but is susceptible to various changes without departing from the scope of the invention. For example, rather than the tree being the wellhead member that supports the tubing hanger, the tubing hanger could land in the wellhead housing or a tubing spool above the wellhead housing, and the tree installed later. In this case, the wellhead member having the sealing surface and containing the wear bushing would be the wellhead housing or tubing spool. Also, if the cable clamps were small enough to pass through the wear bushing, an operator could make up the total desired length of tubing when first running the pump assembly through the wear bushing. If so, the operator would then attach the retrieval tool to the upper end of the tubing and run the retrieval tool on drill pipe, as explained above. When the wear bushing is retrieved, rather than connecting more strings of tubing, the operator could then attach the tubing hanger, cut and secure the cable to the tubing hanger, and lower the assembly on drill pipe. In that alternate method, the cable would not be fed from the reel through the wear bushing while the wear bushing is supported on the cradle.