Abstract:
A system for maneuvering a plug in and out of a tubing hanger mounts to a subsea wellhead assembly. The system includes a tractor and an end effector that are sheltered in a housing. A control cable spools from a reel mounted on the housing and attaches to the tractor. The control cable provides communication from a remotely operated vehicle (ROV) to the tractor and end effector so that commands from the ROV via the control cable control the tractor and end effector. After the housing connects to the wellhead assembly, control signals from the ROV activate the tractor to drive the end effector into the wellhead assembly and command the end effector to set the plug in the tubing hanger, or to remove the plug from the tubing hanger.

Description:
BACKGROUND 
     1. Field of Invention 
     The invention relates generally to a system and method for handling a plug assembly. More specifically, the invention relates to a system and method for installing and/or removing a plug assembly from a tubing hanger subsea. 
     2. Description of Prior Art 
     Subsea wellhead assemblies typically have a high pressure wellhead housing supported in a lower pressure wellhead housing and secured to casing that extends into the well. Usually one or more casing hangers land in the wellhead housing, where the casing hanger being located at the upper end of a string of casing that extends into the well to a deeper depth. A string of tubing generally extends through the casing for producing fluids from the well. Most assemblies include a production tree mounted to the upper end of the wellhead housing for controlling the well fluid. Production trees are typically large and heavy, having a number of valves and controls mounted thereon. 
     One type of tree, which is sometimes referred to as a “conventional” tree, includes a bore for production fluids and a tubing annulus access bore. Wellhead assemblies having conventional trees are formed by landing the tubing hanger in the wellhead housing. Tubing hangers in convention trees generally have a production passage, and an annulus passage that communicates with the tubing annulus surrounding the tubing. A flow circuit is defined through the tubing annulus and production tubing, circulating fluid through the circuit can be used to kill the well or to circulate out heavy fluid during completion. 
     Trees that are sometimes referred to as “horizontal” trees have a single bore in the tree, which is typically the production passage. A horizontal tree is landed before its corresponding tubing hanger is installed, then the tubing hanger is lowered and landed in the tree. The tubing hanger is lowered through the riser, which is typically a drilling riser. In another common type of wellhead system, a concentric tubing hanger lands in the wellhead housing in the same manner as a conventional wellhead assembly. The tubing hanger has a production passage and an annulus passage. However, the production passage is concentric with the axis of the tubing hanger, rather than slightly offset as in conventional tubing hangers and the tree does not have vertical tubing annulus passage. Tubing hangers in vertical trees are usually installed before the tree is landed on the wellhead housing. The tubing is typically run on a landing string through the drilling riser and BOP. Before the drilling riser is disconnected from the wellhead housing, a plug is installed in the tubing hanger as a safety barrier. The plug is normally lowered on a wireline through the landing string. Subsequently, after the tree is installed, the plug is removed through an open water riser that may be used to install the tree. 
     SUMMARY OF THE INVENTION 
     Provided herein is an example of a system for maneuvering a plug in and out of a tubing hanger disposed in a subsea wellhead assembly. In an example embodiment, the system includes a housing selectively coupled with the subsea wellhead assembly; where the housing has an end with an opening that is intersected by a chamber formed in the housing. A tractor is selectively deployed from within the housing that has an attached end effector. The plug is selectively coupled with the end effector, so that when the tractor is deployed from within the housing, the end effector handles the plug in the tubing hanger. In one example, the system further includes a reel mounted on the housing, a control line spooled on the reel that has an end attached to the tractor and is in selective communication with a remotely operated vehicle deployed subsea. An optional hot stab can be mounted on the housing for connecting to the remotely operated vehicle. In one optional example, the chamber registers with a main bore in the subsea wellhead assembly when the housing is coupled with the subsea wellhead assembly. The tractor in one example includes wheel members that project radially outward and into urging contact with an inner surface of the chamber when the tractor is in the housing and into urging contact with a main bore in the subsea wellhead assembly when the tractor is deployed from within the housing. An upper end of the chamber may optionally be subsea. In one embodiment, a seal is defined along an interface between the housing and the wellhead assembly. 
     Also provided herein is an example of a system for plugging a tubing hanger in a subsea wellhead assembly that in an embodiment includes a housing with an open end. In this example, the housing further includes a base at the open end that is sealingly attachable to the wellhead assembly and a closed end opposite the open end. A chamber in the wellhead assembly intersects the open end. A plug tooling assembly is selectively deployable from within the chamber. In an embodiment, the plug tooling assembly is made up of a tractor, an end effector mounted on the tractor, and a plug releasably connected to the end effector. The open end of the housing can attach to the wellhead assembly and the closed end may be disposed subsea. A control cable may optionally be included that provides power and control signals to the plug tooling assembly. In an example, the control cable has an end coupled with the plug tooling assembly and is in communication with a remotely operated vehicle disposed subsea. In an example embodiment, the control cable extends along a passage formed through the closed end and wherein packoffs in the passage define a pressure barrier between the cavity and ambient to the housing. Proximity sensors may optionally be set in the housing and the plug for determining a location of the plug in the housing. 
     Yet further provided herein is a method of handling a plug in a tubing hanger of a subsea wellhead assembly. In one example the method includes enclosing a tractor with an attached end effector in a housing, mounting the housing onto the wellhead assembly so that an upper end of the housing is submerged subsea, deploying the tractor and end effector from the housing into a main bore in the wellhead assembly, and handling the plug in the tubing hanger with the end effector. In one optional example of the method, the step of deploying the tractor involves engaging wheels on the tractor with an inner surface of the housing and an inner surface of the main bore. The method may further include deploying a remotely operated vehicle subsea, engaging a connector on the housing with the remotely operated vehicle, and controlling the tractor and end effector from the remotely operated vehicle through the connector. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
       Some of the features and benefits of the present invention having been stated, others will become apparent as the description proceeds when taken in conjunction with the accompanying drawings, in which: 
         FIG. 1  is a side partial sectional view of an example of a plug installation package in accordance with the present invention. 
         FIG. 2  is a side partial sectional view of an example of the plug installation package of  FIG. 1  being set onto a wellhead assembly in accordance with the present disclosure. 
         FIGS. 3 and 4  are side partial sectional views of an example of the plug installation package installing a plug in a tubing hanger of a wellhead assembly in accordance with the present invention. 
     
    
    
     While the invention will be described in connection with the preferred embodiments, it will be understood that it is not intended to limit the invention to that embodiment. On the contrary, it is intended to cover all alternatives, modifications, and equivalents, as may be included within the spirit and scope of the invention as defined by the appended claims. 
     DETAILED DESCRIPTION OF INVENTION 
     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. 
     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. Accordingly, the improvements herein described are therefore to be limited only by the scope of the appended claims. 
     An example of a wellhead plug tooling package  10  is shown in a partial side sectional view in  FIG. 1 ; which includes a housing  12  shown made up of a shroud  14  with a substantially cylindrical outer surface and a closed end  15  on its upper end. Opposite the closed end  15  is a connector  16  that also has a substantially cylindrical outer surface and an outer diameter extending radially outward past an outer diameter of the shroud  14 . In one example, connector  16  is a type conventionally used in subsea applications. A chamber  18  is shown extending axially through the shroud  14  and connector  16  which intersects an open end  19  disposed on a lower end of the connector  16 . Stowed within the chamber  18  is a plug tooling assembly  20 ; which in the example of  FIG. 1  includes a tractor  22  having wheels  24  that selectively extend radially outward from an axis of the tractor  22 . An end effector  26  mounts on a lower end of the tractor  22  of  FIG. 1  and is shown having a plug  28  is set on its lower end and on a side opposite where the end effector  26  connects with tractor  22 . 
     An optional control cable  30  is shown extending through a passage  32 , where the passage  32  is formed substantially axially through the closed end  15 . Examples of the control cable  30  include a wireline, slickline, cable, and other elements for deploying devices subsea and/or for conveying signals therein. Optional packoffs  34  are illustrated set coaxial within the passage  32  that extend from grooves in the wall of the passage  32  radially inward into the annular space defined between the control cable  30  and surfaces of the passage  32 . In one example of operation, the control cable  30  slides axially within the packoffs  34 , while the packoffs  34  provide a pressure barrier between the chamber  18  and area ambient to the housing  12 , so that when the wellhead plug tooling package  10  is disposed subsea, seawater is prevented from entering the chamber  18  while yet the control cable  30  is able to axially move within the passage  32 . 
     A reel assembly  36  mounts on the housing  12  over the closed end  15  and includes a spool  38 . A length of control cable  30  is shown rolled up on the spool  38  and the spool is supported on a frame  40 . Hot stabs  42 ,  44  are shown set on the frame  40  and are configurable to be engaged by a remotely operated vehicle (ROV)  45  shown disposed adjacent the wellhead plug tooling package  10 . A spindle  46  is included with the frame that extends laterally between vertical members  47  that have lower ends that mount axially onto an upper surface of the closed end  15 . A signal line  48  is shown having an upper end terminating into and connecting with hot stab  44 ; the signal line  48  is disposed in a passage  50  shown extending axially a distance through the shroud  12  and into the connector  16 , then running radially inward within connector  16  and intersect with an inner surface of the chamber  18 . Proximity sensor  52  is shown provided in the end of the passage  50  distal from hot stab  44 , and proximity sensor  54  is illustrated in plug  28 . In the example of  FIG. 1 , the plug  28  is adjacent the lower terminal end of passage  50  so that proximity sensors  52 ,  54  are disposed facing one another. In this position, the position of the plug  28  can be sensed by interaction of the proximity sensors  52 ,  54  that in turn creates a signal through the signal line  48 . It is within the capabilities of those skilled in the art to implement proximity sensors that sense the presence of one another. 
     A cable  56  is shown mounted on the closed end  15 , that in one example of operation provides for deploying the wellhead plug tooling package  10  from above the sea surface, such as from a vessel or platform (not shown). Further, the ROV  45  can be used to provide guidance support when deploying the wellhead plug tooling package  10  on the cable  56 . In this example, actuator arms  60  on the ROV  45  may grapple the wellhead plug tooling package  10  during deployment. Also, the ROV  45  can be controlled from surface by an attached control line  62 . 
     Referring now to  FIG. 2 , an example of the wellhead plug tooling package  10  is shown landed on an upper end of a wellhead assembly  64  that is subsea. The wellhead assembly  64  is mounted into a subsea formation  66 , which is intersected by a wellbore  67  that is in fluid communication with the wellhead assembly  64 . A production tree  68  is included on an upper end of the wellhead assembly  64  and shown mounted onto a wellhead housing  70 ; where a lower end of the wellhead housing  70  anchors in the formation  66 . A main bore  72  in the wellhead assembly  64  (and tree  68 ) registers with the wellbore  67  to provide communication between the wellbore  67  and wellhead assembly  64 . Valves  73  are illustrated in the main bore  72  for controlling flow through the main bore  72 . A tubing hanger  74  is shown landed within the wellhead housing  70 ; a length of tubing  76  depends downward from the tubing hanger  74  and into the wellbore  67 . Shown landed in a portion of the wellhead housing  70  beneath the tubing hanger  74 , is a casing hanger  78  that circumscribes the tubing  76 . A length of casing  80  depends downward from the casing hanger  78  into the wellbore  67 , which also circumscribes the tubing  76 . Shown extending radially outward from the main bore  72  and through the production tree  68  are a production line  82  and auxiliary line  84 . 
     Referring now to  FIG. 3 , the plug tooling assembly  20  is shown having been deployed downward from the housing  12  and into the main bore  72 . In one example, deploying the plug tooling assembly  20  is accomplished by activating a motor (not shown) within the tractor  22  that in turn drives the wheels  24 . Contacting the rotating wheels  24  against the walls of the chamber  82  and main bore  72  downwardly urge the plug tooling assembly  20  into the wellhead assembly  64 . Further, in the example of  FIG. 3 , valves  73  are actuated to an open position thereby allowing passage there through of the plug tooling assembly  20 . Further in the example of  FIG. 3 , the plug  28  is shown set within the tubing hanger  74  and in a position for plugging the wellhead assembly  64 . Setting the plug  28  in the tubing hanger  74  as shown defines a flow barrier within the main bore  72 . Further illustrated is how proximity sensors  52 ,  54  are axially spaced apart from one another, so that by monitoring signals from proximity sensor  52  as described above, it can be confirmed that the plug  28  has deployed from within the housing  12 . 
     Further illustrated in the example of  FIG. 3 , that that arm  60  of the ROV  45  is engaging hot stab  42  thereby creating communication from the ROV  45  into the plug tooling assembly  20 . Communication between ROV  45  and plug tooling assembly  20  is via a connection between a receptacle (not shown) in hot stab  42  and plug (not shown) in arm  60 , and communication through control cable  30 . Examples of operation exist wherein the plug tooling assembly  20  is gravity deployed from the housing  12  and into the wellhead assembly  64  instead of, or in addition to, activation of the wheels  24  on tractor  22 . 
       FIG. 4  illustrates in a side partial side sectional view that tractor  22  and end effector  26  have been retracted within housing  12  leaving plug  28  within tubing hanger  74 . In the example of  FIG. 4 , latches  86  are shown extended radially outward and within a profile  88  provided on an inner surface of the tubing hanger  74 . In one example, the latches  86  are deployed via mechanical operation of the end effector  26 . An example of an end effector  22  suitable for use herein can be found in U.S. Pat. No. 7,121,344 issued Oct. 17, 2006, and assigned to the assignee of the present application. U.S. Pat. No. 7,121,344 is incorporated by reference herein in its entirety for all purposes. In another example, the plug  28  of  FIG. 4  can be retrieved from within tubing hanger  74  by reversing the above described process, that is landing the housing  12  with enclosed tractor  22  and end effector  26 , deploying the tractor  22 , and end effector  26  into tubing hanger  74 , retracting the latches  86  from within the grooves  88 , and coupling the end effector  26  with plug  28 . Once attached to the end effector  26 , the plug can be removed from within tubing hanger  74  by drawing the tractor  22  and end effector  26  back into the housing  22 . The position of the plug within the housing  12  may be confirmed when proximity sensor  52 ,  54  are appropriately positioned thereby providing a signal through signal line  48 , which may optionally be monitored by ROV  45  via its optional connection to hot stab  44  ( FIG. 1 ). In one example, after confirming the plug  28  is within housing  12 , the housing  12  can be detached from the wellhead assembly  64  and removed therefrom so that production from the wellbore  67  can be initiated. 
     Advantages of the system and method described herein include retrieving a plug from a tubing hanger without the need for a riser extending to the surface. Because a riser is unnecessary, a production tree can be efficiently removed on a lift wire (not shown). An example of this is provided in U.S. Pat. No. 6,968,902 issued Nov. 29, 2005, and assigned to the assignee of the present application. U.S. Pat. No. 6,968,902 is incorporated by reference herein in its entirety for all purposes. Moreover, because installing and/or removing the plug can be accomplished by use of an ROV  45 , an umbilical to the surface for the plug tool is unnecessary. 
     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 a presently preferred embodiment of the invention has been given for purposes of disclosure, numerous changes exist in the details of procedures for accomplishing the desired results. For example, the tool may be additionally used to install/retrieve at least another plug set below the tubing hanger at a lower depth within the production tubing system. 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.