Patent Publication Number: US-10760366-B2

Title: Coiled tubing connector to electrical submersible pump

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     This application claims priority to provisional application 62/675,813, filed May 24, 2018. 
    
    
     FIELD OF THE DISCLOSURE 
     This disclosure relates in general to electrical submersible well pumps (ESP), and in particular to a connector for connecting coiled tubing containing a power cable to the ESP. 
     BACKGROUND 
     Electrical submersible well pumps are often used to pump liquids from hydrocarbon producing wells. A typical ESP includes a pump driven by an electrical motor. Production tubing, which comprises pipes having threaded ends secured together, supports the ESP in most installations. The pump normally pumps well fluid into the production tubing. A power cable extends alongside the production tubing to the motor for supplying power. Installing and retrieving the ESP requires a workover rig to pull the production tubing. 
     In other installations, coiled tubing supports the ESP. The coiled tubing comprises a continuous length or segment of steel tubing that can be wound on a large reel at the surface before deploying and after retrieving. A power cable with power conductors for supplying power to the motor extends through the coiled tubing. The pump discharges well fluid up the annulus surrounding the coiled tubing. A coiled tubing installation allows the ESP to be installed and retrieved without the need for a workover rig. 
     A connector secures the coiled tubing to the upper end of the motor, which is located above the pump. The motor is filled with a dielectric lubricant for lubricating the bearings. A seal section between the motor and the pump has a bellows or flexible bag that contracts and expands to equalize the pressure of the dielectric lubricant with the well fluid pressure surrounding the motor. The connector also has electrical connections to connect the motor wires with the conductors in the power cable. In the prior art, the connector will have features to reduce the chance for well fluid that might leak into the connector from migrating down into the motor. At least some prior art connectors are filled with a dielectric fluid that immerses the electrical connections in the connector. A bellows or check valve may have been used to accommodate thermal expansion of the dielectric fluid in the connector. 
     Also, some prior art connectors have the ability to part in the event the ESP becomes stuck in the well, enabling the operator to retrieve the coiled tubing then run back in with a fishing string to engage and pull the stuck ESP from the well. 
     SUMMARY 
     An apparatus connects an electrical submersible pump assembly (ESP) to a string of coiled tubing containing a power cable having power conductors. The ESP and coiled tubing are adapted to be installed within a well. The ESP has a pump, a motor, and a pressure equalizer for reducing a pressure difference between motor lubricant in the motor and well fluid surrounding the motor. The apparatus comprises a tubular housing configured to connect between a lower end of the coiled tubing and an upper end of the motor. Upper and lower barriers in the housing define an upper chamber above the upper barrier, a center chamber between the upper and lower barriers, and a lower chamber below the lower barrier. Upper electrical terminals in the upper barrier are configured to connect to the conductors of the power cable, and lower electrical terminals in the lower barrier are configured to connect to motor leads of the motor. Electrical conductor members in the center chamber extend between the upper and the lower electrical terminals in the upper and lower barriers. Upper chamber dielectric fluid, center chamber dielectric fluid, and lower chamber dielectric fluid fill the upper, center and lower chambers, respectively. The upper chamber dielectric fluid, the center chamber dielectric fluid and the lower chamber dielectric fluid are sealed from each other by the upper and lower barriers. An upper opening in the housing communicates an interior of the coiled tubing with the upper chamber dielectric fluid, enabling thermal expansion of the upper chamber dielectric fluid into the interior of the coiled tubing. The lower chamber is configured to be in fluid communication with motor lubricant in the motor, enabling thermal expansion of the lower chamber dielectric lubricant through the pressure equalizer of the ESP. The center chamber has thermal expansion means for allowing thermal expansion of the center chamber dielectric fluid. 
     The center chamber thermal expansion means operates independently of the thermal expansions of the lower chamber dielectric fluid and the upper chamber dielectric fluid. 
     The center chamber thermal expansion means comprises a container located outside of the center chamber. A conduit has an open end in the center chamber for receiving center chamber dielectric fluid. The conduit extends through one of the barriers into the container to allow thermal expansion of the center chamber dielectric fluid. 
     In the embodiments shown, the conduit extends through the upper barrier. In the first embodiment, the container joins the conduit and comprises a capillary line within the coiled tubing. 
     In the second embodiment, a flexible container is located in one of the upper and lower chambers. The container has an exterior immersed in the dielectric fluid within said one of the upper and lower chambers. The conduit extends from the center chamber to an interior of the flexible container to admit center chamber dielectric fluid. 
     In each of the embodiments, the conduit extends through the upper barrier and has an open end in the center chamber for admitting the center chamber dielectric fluid. In the second embodiment, a bellows located in the upper chamber has one side immersed in the upper chamber dielectric fluid and another side in contact with the center chamber dielectric fluid in the conduit. 
     The center chamber dielectric fluid may comprise a heavier fluid and a lighter fluid. 
     In the first embodiment, the upper opening in the housing communicates upper chamber dielectric fluid with an annulus between the power cable and the coiled tubing. 
     In the embodiments shown, the housing has upper and lower housing portions. A parting mechanism selectively allows the upper housing portion to be separated from the lower housing portion to allow retrieval of the coiled tubing in the event the ESP is stuck within a well. The lower barrier is located within the lower housing portion, preventing well fluid from contact with the motor leads after the upper housing portion has separated from the lower housing portion. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic side view of an electrical submersible pump connected to coiled tubing with a connector in accordance with this invention. 
         FIG. 2  is a sectional view of the coiled tubing of  FIG. 1  taken along the line  2 - 2  of  FIG. 1 . 
         FIG. 3  is a schematic sectional view of one embodiment of the connector of  FIG. 1 . 
         FIG. 4  illustrates an upper portion of the connector of  FIG. 3  parted from the lower portion. 
         FIGS. 5A, 5B and 5C  comprises a sectional view in more detail of an another embodiment of the connector of  FIG. 1 . 
     
    
    
     DETAILED DESCRIPTION OF THE DISCLOSURE 
     The method and system of the present disclosure will now be described more fully hereinafter with reference to the accompanying drawings in which embodiments are shown. The method and system of the present disclosure may be in many different forms and should not be construed as limited to the illustrated embodiments set forth herein; rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey its scope to those skilled in the art. Like numbers refer to like elements throughout. In an embodiment, usage of the term “about” includes +/−5% of the cited magnitude. In an embodiment, usage of the term “substantially” includes +/−5% of the cited magnitude. The terms “upper” and “lower” are used only for convenience as the well pump may operate in positions other than vertical, including in horizontal sections of a well. 
     It is to be further understood that the scope of the present disclosure is not limited to the exact details of construction, operation, exact materials, or embodiments shown and described, as modifications and equivalents will be apparent to one skilled in the art. In the drawings and specification, there have been disclosed illustrative embodiments and, although specific terms are employed, they are used in a generic and descriptive sense only and not for the purpose of limitation. 
     Referring to  FIG. 1 , a well casing  11  has a string of production tubing  13 . Downhole equipment that may be an electrical submersible pump (ESP)  15  is located within production tubing  13 . In this example, ESP  15  has an electrical motor  17  on the upper end. A seal section  19  connects to the lower end of motor  17  and has a pressure equalizer, which may be a flexible container such as a bellows or elastomeric bag to reduce a pressure differential between dielectric lubricant in motor  17  and well fluid on the exterior. A pump  21  secures to the lower end of seal section  19 . Pump  21  may be a centrifugal pump with a large number of stages, each stage having an impeller and a diffuser. Pump  21  has an intake  25  that extends through a packer  23  for drawing in well fluid. Pump  21  has a discharge  27  on its upper end that discharges well fluid into an annulus surrounding seal section  19  and motor  17  within production tubing  13 . Other configurations and types of ESP  15  are feasible. 
     A string of coiled tubing  29  connects to a connector  47  on the upper end of motor  17  and supports ESP  15  within production tubing  13 . The terms “lower”, “upper” and the like are used only for convenience because ESP  15  may be operated in other orientations, including horizontal. Coiled tubing  29  is a continuous length of a steel tube that has a capability of being wound around a large reel when out of the well. 
     A conventional hanger (not shown) supports an upper end portion of coiled tubing  29  within a wellhead assembly or tree  31 . Well fluid being pumped by ESP  15  flows from production tubing  13  into tree  31  and out a flow line  33 . Coiled tubing  29  extends upward through wellhead assembly  31  and is electrically connected to an adjacent controller or power supply  35 . 
     Referring to  FIG. 2 , coiled tubing  29  contains an electrical power cable  36  for supplying three-phase electrical power to motor  17  ( FIG. 1 ). Power cable  36  has three power conductors  37  that are arranged 120 degrees apart from each other relative to a centerline of power cable  36 . Each power conductor  37  is encased in one or more separate electrical insulation layers  39 . Also, the three power conductors  37  and their insulation layers  39  may be embedded within an elastomeric jacket  41  extruded over power conductors  37 . One or more capillary lines or tubes  43  (three shown) could also be embedded within jacket  41  for fluid flow. 
     The exterior of jacket  41  is cylindrical and may have a metal strip or armor  45  wrapped helically around it. There is no seal between armor  45  and the inner wall surface of coiled tubing  29 , creating a thin inner annulus  46  for fluid to enter. Power cable  36  may be installed in coiled tubing  29  while coiled tubing  29  is being formed into a cylindrical shape and seam welded. Alternately, power cable  36  may be pulled into coiled tubing  29  after coiled tubing  29  has been manufactured. Power cable  36  normally lacks the ability to support its own weight in a well, thus various arrangements may be made to frictionally transfer the weight of power cable  36  to coiled tubing  29  along the length of coiled tubing  29 . 
     Referring to  FIG. 3 , connector  47  in this embodiment is shown schematically. Connector  47  has a head  49  with a set of slips  51  in an axial upper opening  52 . Coiled tubing  29  extends downward through opening  52 , and slips  51  grip the lower end portion of coiled tubing  29 . Connector  47  has a tubular upper housing  53  and a tubular lower housing  55 . In this example, a wall  56  on the lower end of upper housing  53  overlaps an upper wall portion of lower housing  55 . Shear screws or pins  57  extend through lateral holes in wall  56  and lower housing  55  to join the lower end of upper housing  53  to the upper end of lower housing  55 . Alternately, the overlapping wall  56  could be on the upper end of lower housing  55 . Shear pins  57  serve as a parting mechanism to allowing upper housing  53  to separate from lower housing  55  in the event ESP  15  becomes stuck. Lower housing  55  secures to the head of motor  17  ( FIG. 1 ) in a conventional manner. 
     An upper barrier or seal  59  of electrical insulation material seals across the interior of upper housing  53 , and a lower barrier or seal  61  of electrical insulation material seals across the interior of lower housing  55 . Upper and lower seals  59 ,  61  are fixed against axial movement. Upper and lower seals  59 ,  61  may be formed of a rigid fluoropolymer such as PEEK, and have elastomeric seal rings (not shown) that seal them to the sidewalls of upper and lower housing  53 ,  55 . 
     Insulated conductor rods  63 , one for each power conductor  37  ( FIG. 2 ), have upper ends sealed in passages in upper seal  59  and lower ends sealed in passages in lower seal  61 . Electrical splices  65  above upper seal  59  connect power cable conductors  37  to splice conductors  67 , which in turn sealingly enter passages in upper seal  59 . Upper seal electrical connections or terminals  69  in upper seal  59  electrically join splice conductors  67  with conductor rods  63 . Lower seal  61  has lower seal electrical connections terminals  71  that electrically join conductor rods  63  with motor wires  73 . Electrical splices  65  and upper and lower electrical connections  69 ,  71  may be a variety of types. 
     Upper seal  59  defines an upper chamber  75  that is in fluid communication via opening  52  with inner annulus  46  between power cable armor  45  ( FIG. 2 ) and coiled tubing  29 . Upper seal  59  and lower seal  61  define between them a center chamber  77 . Lower seal  61  defines below it a lower chamber  79 . 
     An upper chamber dielectric fluid or oil  81  fills upper chamber  75 , providing additional electrical insulation around splices  65  and upper seal electrical connections  69 . A center chamber dielectric fluid or oil  83   a ,  83   b  optionally may be of two weights or gravities. The lighter weight dielectric fluid  83   a  migrates upward into contact with the lower side of upper seal  59 , overlying heavier weight dielectric fluid  83   b . The heavier weight dielectric fluid  83   b  gravitates downward into contact with the upper side of lower seal  61 . The weights of dielectric fluid  83   a ,  83   b  are selected such that the weight of the typical well fluid, mostly water, will be less than heavier weight dielectric fluid  83   b  and more than lighter weight dielectric fluid  83   a . As a result, if any well fluid manages to leak into the interior of center chamber  77 , it will gravitate to a position between lighter weight dielectric fluid  83   a  and heavier weight dielectric fluid  83   b . This positioning reduces the chances for the well fluid to come into contact with upper and lower seal electrical connections  69 ,  71 . 
     A lower chamber dielectric fluid or oil  85  fills lower chamber  79 . Lower chamber  79  has a lower passage that communicates lower chamber  79  with the flexible container in seal section  19  and the interior of motor  17  ( FIG. 1 ). Lower chamber dielectric fluid  85  is thus in fluid communication with the lubricating oil in seal section  19  and motor  17  ( FIG. 1 ) and may be the same. Lower seal  61  seals lower chamber dielectric fluid  85  from center chamber dielectric fluids  83   a ,  83   b . Upper seal  59  seals upper chamber dielectric fluid  81  from center chamber dielectric fluids  83   a ,  83   b.    
     Center chamber dielectric fluids  83   a ,  83   b  will expand thermally due to operation of motor  17  and the well temperature. Also, when motor  17  is shut down, the cooling of dielectric fluids  83   a ,  83   b  causes them to contract. However, the volume of center chamber  77  is fixed. A thermal expansion device, which includes a conduit or tube  87 , will accommodate the expansion and contraction of dielectric fluid  83   a ,  83   b . The thermal expansion devices for center chamber  77  operates independently of the thermal expansion and contraction occurring in the upper chamber  75  and lower chamber  79 . 
     In this example, thermal expansion tube  87  leads upward through upper chamber  75  and joins one of the capillary tubes  43  ( FIG. 2 ) in power cable  36 . Thermal expansion tube  87  may be a rigid tube that extends downward through upper chamber  75  and sealingly through upper seal  69 . Thermal expansion tube  87  has an open lower end within center chamber  77 . The capillary tube  43  joined by thermal expansion tube  87  serves as a container for receiving thermally expanding center chamber dielectric fluid  83   a ,  83   b . The upper end of capillary tube  43  will be at the upper end of coiled tubing  29  at or adjacent wellhead assembly  31  ( FIG. 1 ) and may be open. Much of the capillary tube  43  joined by thermal expansion tube  87  will be empty, allowing center chamber dielectric lubricant  83   a ,  83   b  to migrate into these upper portions in response to a thermal increase in volume. Also, upon cooling, center chamber dielectric lubricant  83   a ,  83   b  can migrate back downward into center chamber  77 . In this example, the fluid pressure within center chamber  77  will be based on the column, if any, of dielectric lubricant  83   a ,  83   b  in capillary tube  43 , not the hydrostatic pressure of well fluid on the exterior of connector  47 . 
     Thermal expansion and contraction of upper chamber dielectric fluid  81  causes some of it to migrate upward and downward in annulus  46  between power cable  36  and coiled tubing  29  ( FIG. 2 ). Annulus  46  extends the length of coiled tubing  29  and may be open at the upper end. The fluid pressure within upper chamber  75  will be based on the column, if any, of upper chamber dielectric fluid  81  in annulus  46 , not the hydrostatic pressure of well fluid on the exterior of connector  47 . 
     Lower chamber dielectric lubricant  85  will be at the same pressure as the motor lubricant, which is equalized with well fluid pressure by the pressure equalizer in seal section  19  ( FIG. 1 ). Seal section  19  has a bellows or flexible bag that will handle thermal expansion and contraction of lower chamber dielectric fluid  85 . Upper chamber dielectric fluid  81  and center chamber dielectric fluid  83   a ,  83   b  will be at a lesser pressure than the pressure of lower chamber dielectric fluid  85  because their pressures are not pressure compensated by seal section  19  to equalize with well fluid pressure. 
     Periodically, ESP  15  ( FIG. 1 ) must to be retrieved for maintenance. ESP  15  could be stuck in tubing  13  due to sand accumulation between ESP  15  and tubing  13 . Coiled tubing  29  may not have adequate strength to pull ESP  15  loose. As illustrated in  FIG. 4 , shear pins  57  ( FIG. 3 ) are designed to shear at a lower level than the tensile strength of coiled tubing  29 . Upper housing  53  will part from lower housing  55 , allowing coiled tubing  29  to be retrieved along with upper housing  53 . Lower seal  61  remains sealed in lower housing  55  and will continue to keep lower chamber  79  sealed from well fluid. The upward movement of upper housing  53  opens the lower end of center chamber  77 , admitting well fluid. Conductor rods  63  may remain affixed to upper seal  59 . Upper seal  59  may continue to seal in upper housing  53 . The operator may then run in with a fishing string (not shown) of greater tensile strength than coiled tubing  29  that will engage lower housing  55  and pull it along with motor  17 , seal section  19  and pump  21  from the well. 
     Referring to  FIG. 5A-C , connector  89  is shown in more detail than connector  47  of  FIGS. 3-4 . A collet  91  has internal transverse grooves  93  that grip the exterior of coiled tubing  29  ( FIG. 1 ) when head  94  is tightened. Three collet support columns  95  (only one shown) are secured on their lower ends to a collet base  97 ; the upper ends of collet support columns  95  support collet  91  against downward movement when head  94  is tightened. Only one of the three electrical splices  99  is shown, and the power conductors  37  ( FIG. 2 ) are not illustrated. A flexible container, which may be a bellows  101  that can expand and contract in volume, is positioned alongside electrical splices  99 . An expansion tube  103  leads to the lower end of bellows  101 . 
     Collet base  95  rests on a threaded breakout sub  105 , which secures to the lower end of an upper housing section  107  and may be considered to be a part of upper housing section  107 . The upper end of upper housing section  107  secures to head  94 . Breakout sub  105  optionally has a port  109  extending from its upper end within upper housing section  107  to its exterior, as shown in  FIG. 5B . Port  109  has an upper sealed fitting  111  for connecting to one of the capillary tubes  43  ( FIG. 3 ). Head  94 , upper housing section  107  and breakout sub  105  define an upper dielectric fluid chamber  113 . A lower fitting  115  is located at the lower end of port  109 , as shown in  FIG. 5B . Lower fitting  115  may connect to a capillary tube (not shown) extending downward to the lower end of ESP  15  ( FIG. 1 ) for delivering chemicals or other fluids pumped down one of the capillary tubes  43  ( FIG. 2 ). 
     An upper barrier or seal  117  seals a central bore in upper breakout sub  105 , defining a lower end of upper dielectric fluid chamber  113 . Three upper seal electrical connectors or terminals  119  (only one shown) connect to electrical splice conductors  121  extending down from splices  99 . The upper ends of three insulated conductor rods  123  (only one shown) join upper seal electrical connectors  119 . 
     Another upper housing portion  125  secures by threads to the lower end of breakout sub  105 . A collet  127  secures to a lower portion of breakout sub  105  and has fingers on its lower end that are biased outward toward a released position. A lock or restraint ring  129  traps the fingers of collet  127  in a radially inward locked position in engagement with a shoulder sleeve  131  while restraint ring  129  is in the upper released position. Hydraulic fluid pressure supplied from one of the capillary tubes  43  ( FIG. 2 ) will communicate through passages (not shown) to an upper side of restraint ring  129 . Once the pressure is adequate, it will shear pins  132  ( FIG. 5C ), causing restraint ring  129  to move downward. The downward movement frees the fingers of collet  127  to spring outward, releasing collet  127  from shoulder sleeve  131 . 
     Shoulder sleeve  131  surrounds a male sub  133  that extends upward into sealing but not securing engagement with breakout sub  105 . Male sub  133  is held in sealing engagement with breakout sub  105  by collet  127 , shoulder sleeve  131  and restraint ring  129 . Male sub  133  extends downward in upper housing portion  125  and has a center bore or chamber  135  through which conductor rods  123  extend. Referring to  FIG. 5C , the lower end of male sub  133  secures by threads to a lower housing section  137 . A check valve  139  may be employed to vent fluid displaced by the downward movement of restraint ring  129 . 
     A lower barrier or seal  141  seals a bore in lower housing  137 , defining a lower end of center chamber  135 . Lower seal  141  has three electrical terminals or connectors  143  (only one shown), each sealed within a passage for engagement by the lower end of one of the conductor rods  123 . A motor wire sealing arrangement  145  electrically connects one of the motor wires (not shown) to the lower side of one of the lower seal electrical connectors  143 . Lower housing  137  secures by threads to an adapter  147 . Adapter  147  secures to a base  149  for connection to motor  17  ( FIG. 1 ). 
     Lower seal  141  defines the upper end of a lower dielectric fluid chamber  151  that will be filled with and in communication with lubricant in motor  17  and seal section  19  ( FIG. 1 ). Center dielectric fluid chamber  135  will be filled with a central chamber dielectric fluid. As in the first embodiment, the dielectric fluid in center chamber  135  may be of two different weights. Upper chamber  113  ( FIG. 5A ) will be filled with a dielectric fluid that is in communication with the annulus  46  between power cable  36  and coiled tubing  29  ( FIG. 2 ). Upper seal  117  seals the fluid in upper chamber  113  from the fluid in center chamber  135 . 
     Thermal expansion tube  103  has an open lower end in center chamber  135 , thus dielectric fluid in center chamber  135  will be in communication with the interior of bellows  101 . Bellows  101  may be located in a shell  153  with openings to admit dielectric fluid in upper chamber  113 . The exterior of bellows  101  is thus immersed in dielectric fluid in upper chamber  113 . Heat may cause the dielectric fluid in center chamber  135  to expand, increasing the volume of bellows  101  to accommodate the increase in volume of dielectric fluid. Cooling of the dielectric fluids when motor  17  is shut down may cause bellows  101  to contract. Expansion of dielectric fluid in upper chamber  113  is accommodated by allowing some of the fluid to migrate up annulus  46  between power cable  36  and coiled tubing  29  ( FIG. 2 ). Thermal expansion of dielectric fluid in lower chamber  151  is handled by the flexible container or pressure equalizer in seal section  19  ( FIG. 1 ). 
     Upon retrieval, if ESP  15  is stuck, the operator may apply hydraulic fluid pressure to one of the capillary tubes  43  ( FIG. 3 ), causing restraint ring  129  to move downward. The downward movement frees the fingers of collet  127  to spring out, releasing male sub  133  from breakout sub  105 . An upward pull will separate upper housing section  125  from lower housing section  137 , allowing upper housing sections  107  and  125  to be retrieved along with conductor rods  123  and breakout sub  105 . Male sub  133  remains attached to lower housing section  137 . Lower seal  141  seals the upper end of lower dielectric fluid chamber  151  from well fluid that enters central dielectric fluid chamber  135  after upper housing section  125  releases from lower housing section  137 . Subsequently, an operator may lower a fishing string with a fishing tool to engage male sub  133 . 
     The present invention described herein, therefore, is well adapted to carry out the objects and attain the ends and advantages mentioned, as well as others inherent therein. While only a few embodiments of the invention have been given for purposes of disclosure, numerous changes exist in the details of procedures for accomplishing the desired results. These and other similar modifications will readily suggest themselves to those skilled in the art, and are intended to be encompassed within the spirit of the present invention disclosed herein and the scope of the appended claims.