Abstract:
An apparatus adapted for removing a plug ( 12 ) from a subsea Christmas tree ( 10 ) is disclosed which includes a housing ( 84 ), a distal end of the apparatus that is adapted to engage the plug ( 12 ) and a fluid passage ( 83 ) formed in the housing ( 84 ) for use in directing a stream of fluid toward the plug ( 12 ) to remove debris ( 90 ) from above the plug ( 12 ). Also disclosed is a method for removing debris ( 90 ) from a subsea Christmas tree ( 10 ) including connecting a marine riser and a blowout preventer (BOP) ( 60 ) to a subsea Christmas tree ( 10 ), lowering a plug removal tool ( 80 ) through the marine riser to the Christmas tree ( 10 ), the plug removal tool ( 80 ) having a fluid passage ( 83 ) formed therein, and forcing a fluid down the marine riser and through the fluid passage ( 83 ) in the plug removal tool ( 80 ) to wash out debris ( 90 ) in the Christmas tree ( 10 ).

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    The present invention is generally related to the field of subsea wells and tools, and more particularly, to methods and tools for retrieving wire line plugs from subsea wells, which allows debris to be removed from on top of the plugs and riser hydrostatic pressure effects to be overcome. 
         [0003]    2. Description of the Related Art 
         [0004]    A horizontal Christmas tree is a device that is commonly employed on many subsea wells. Such horizontal trees utilize wire line plugs. All suppliers of this type of tree have problems with debris accumulating on the plugs. A solution, which allowed the plugs to be pulled without preliminary debris clearing, and or under conditions where riser hydrostatic pressure is greater than wellhead pressure would be a significant completive advantage. 
         [0005]    Debris from drilling and the completion riser systems accumulate on top of horizontal Christmas trees settling in the upper bore of the tubing hanger over the wire line plugs. The wire line plugs must be removed to allow access to the well bore. Removal of the debris is costly with current methods and increases in cost with water depth and rig rates, both of which are increasing. Furthermore, in deep water applications, the hydrostatic pressure in the completion riser is sometimes in excess of the wellhead pressure. This produces a downward load on the load on the wireline plug which can be larger than the wire tensile capacity. This prevents or complicates plug retrieval. 
         [0006]    When clearing out debris from the wellhead or Christmas tree, the normal practice is to run a wire line bailer or pump to remove the debris. It is also possible to run coiled tubing into the well to wash out the debris before the wire line operations are performed. The use of coiled tubing allows a higher pulling load to be applied to the plug overcoming some of the riser-wellhead pressure balance problems. Special pulling tools may also be used to the same effect. 
         [0007]    The current practice is an incomplete solution to the problem because the bailing tool must be run to establish if debris is present above the plug. It is then run repeatedly, which removes a limited amount of debris with each trip of the tool from the surface to the top of the debris, until it fails to retrieve debris, which indicates clearance. All of these trips cost additional time and money if the clearance can be accomplished without a separate wire line operation. Coiled tubing can be run into the well through the production riser to wash the debris from above the top of the plugs. This is considered to be a prohibitively expensive procedure due to extra equipment mobilization and the complexity of the operation. Special pulling tools, like the normal wireline pulling tools, cannot be used until the debris has been removed by separate operations. 
         [0008]    The present invention is directed to an apparatus and methods for solving, or at least reducing the effects of, some or all of the aforementioned problems. 
       SUMMARY OF THE INVENTION 
       [0009]    The following presents a simplified summary of the invention in order to provide a basic understanding of some aspects of the invention. This summary is not an exhaustive overview of the invention. It is not intended to identify key or critical elements of the invention or to delineate the scope of the invention. Its sole purpose is to present some concepts in a simplified form as a prelude to the more detailed description that is discussed later. 
         [0010]    In one illustrative embodiment, an apparatus adapted for removing a plug from a subsea Christmas tree is disclosed which comprises a housing, a distal end of the apparatus that is adapted to engage the plug, and a fluid passage formed in the housing that is adapted for use in directing a stream of fluid toward the plug to remove debris from above the plug. 
         [0011]    In another illustrative embodiment, an apparatus adapted for removing a plug from a subsea Christmas tree is disclosed which comprises a housing, a distal end of the apparatus that is adapted to engage the plug, a fluid passage formed in the housing, the exit of which defines a nozzle that is adapted for use in directing a stream of fluid toward the plug to remove debris from above the plug, and a tubing hanger running tool having a bore formed therein, wherein the housing is moveably positioned within the bore. 
         [0012]    In yet another illustrative embodiment, the invention consists of a wire line plug pulling tool with a fluid path which begins above an enlarged outside diameter section and exits at or close to the end of the tool which engages the wire line plug. The tool&#39;s enlarged outer section interacts with a reduced internal bore of the completion riser assembly, which creates a fluid flow restriction past the outside of the tool. This restriction forces any fluid pumped down the production riser through the fluid path of the tool exiting at high velocity at the end of the tool, thereby washing debris away from the pulling tool and plug interface. Furthermore, fluid pressure applied by this restriction creates a net upward or pulling load on the tool when the central wash port is closed. 
         [0013]    No known method or tool combines the ability to remove debris from the tool-plug interface with the tool that is used to pull the plug and/or produce a net upward or pulling load on the tool using pressure from the surface. 
         [0014]    In one illustrative embodiment, a method for removing debris from a subsea Christmas tree is disclosed which comprises connecting a marine riser and a blowout preventer (BOP) to a subsea Christmas tree, lowering a plug removal tool through the marine riser to the Christmas tree, the plug removal tool having a fluid passage formed therein, and forcing a fluid down the marine riser and through the fluid passage in the plug removal tool to wash out debris in the Christmas tree. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS  
         [0015]    The invention may be understood by reference to the following description taken in conjunction with the accompanying drawings, in which like reference numerals identify like elements, and in which: 
           [0016]      FIG. 1  is a cross-sectional view showing a subsea test tree with a tubing hanger installation tool; 
           [0017]      FIG. 2  is a cross-sectional view showing the tool suspended above the tubing hanger; 
           [0018]      FIG. 3  is a cross-sectional view showing the tool latched to the wireline plug; 
           [0019]      FIG. 4  is a cross-sectional view showing the tool in a second mode of operation; 
           [0020]      FIG. 5  is a cross-sectional view showing the tool in a third mode of operation; 
           [0021]      FIG. 6  is a cross-sectional view showing the tool in a fourth mode of operation; 
           [0022]      FIG. 7  is a cross-sectional view showing a second embodiment of the invention; and 
           [0023]      FIG. 8  is a cross-sectional view similar to  FIG. 7  showing the plug removal operation. 
       
    
    
       [0024]    While the invention is susceptible to various modifications and alternative forms, specific embodiments thereof have been shown by way of example in the drawings and are herein described in detail. It should be understood, however, that the description herein of specific embodiments is not intended to limit the invention to the particular forms disclosed, but on the contrary, the intention is to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the invention as defined by the appended claims. 
       DETAILED DESCRIPTION OF THE INVENTION  
       [0025]    Illustrative embodiments of the invention are described below. In the interest of clarity, not all features of an actual implementation are described in this specification. It will of course be appreciated that in the development of any such actual embodiment, numerous implementation-specific decisions must be made to achieve the developers&#39; specific goals, such as compliance with system-related and business-related constraints, which will vary from one implementation to another. Moreover, it will be appreciated that such a development effort might be complex and time-consuming, but would nevertheless be a routine undertaking for those of ordinary skill in the art having the benefit of this disclosure. 
         [0026]    The present invention will now be described with reference to the attached figures. The words and phrases used herein should be understood and interpreted to have a meaning consistent with the understanding of those words and phrases by those skilled in the relevant art. No special definition of a term or phrase, i.e., a definition that is different from the ordinary and customary meaning as understood by those skilled in the art, is intended to be implied by consistent usage of the term or phrase herein. To the extent that a term or phrase is intended to have a special meaning, i.e., a meaning other than that understood by skilled artisans, such a special definition will be expressly set forth in the specification in a definitional manner that directly and unequivocally provides the special definition for the term or phrase. 
         [0027]    Referring to  FIG. 1 , a flow completion assembly  10 , commonly referred to as a horizontal tree completion, is shown in the installation or workover mode of operation. In either of these modes of operation, a blowout preventer (BOP)  60  is connected to the top of the tubing spool  14  and a tubing hanger running tool (THRT)  70  is attached to the top of the tubing hanger  18 . A subsea test tree (SSTT)  63  is normally connected to the top of the THRT  70 . The BOP includes an internal BOP bore  61 , at least one set of rams  65  which is capable of sealing against the THRT  70 , and at least one choke and kill line  62  for providing communication between the BOP bore  61  below the rams  65  and a surface vessel (not shown). At least two valves  64  are provided to secure any wellbore pressure from under the BOP rams  65 . This combination of BOP functions and SSTT  63  provide the standard subsea safety package for the installation or workover mode of operation. The THRT  70  or the SSTT  63  includes a smooth, or seal, bore  75 , which is larger than the wireline plugs  11 ,  12  and smaller in diameter than the riser-SSTT bore above and the THRT bore below. A landing shoulder  74  is provided above or below the reduced bore  75 . In addition the THRT  70  comprises an internal bore  76  or production port, a production stab  71 , which connects to the production bore  26  of the tubing hanger  18 . This production stab may be removed, or constructed to move axially, to open a flow path from the production bore  26  of the tubing hanger  18  to flow ports  77  through the THRT  70  and out of the choke and kill line  62  of the BOP  60 . Flow may also be possibly established between the outside diameter of the THRT  70  and the BOP bore  61 . Alternatively or additionally, a sleeve valve  72 , or other type of valve, may be included in the THRT  70  to allow flow from the production bore  26  through the THRT internal bore  76  and ports  73  to exit out of the choke and kill line  62  of the BOP  60 . Either or both of these flow paths may be utilized to evacuate debris that has been washed from the well bore, in particular from on top of either of two closure members  11 ,  12 . These closure members are normally wireline plugs. When the wireline plugs  11 ,  12  are removed, fluid flow, in the reverse direction, from the surface vessel (not shown) may be useful in balancing the well production bore pressure or killing the well. This capability is particularly important if the subsea test tree SSTT  63  has failed and fluid cannot be pumped down the production-completion riser system bore. 
         [0028]    Referring to  FIG. 2 , a wireline plug pulling tool  80  is shown suspended on a shoulder  85  mating with the landing shoulder  74 , which is part of the THRT  70 . The plug pulling tool  80  is free to move vertically upward. The wireline plug pulling tool  80  may be run with the THRT, SSTT and completion riser (not shown) and not attached to the wireline unit during installation, alternatively the wireline plug pulling tool  80  may be installed with the wireline unit after the THRT, SSTT and completion riser (not shown). The plug pulling tool  80  is equipped with a wireline fishneck  81 . This fishneck is used to connect to the wireline unit remotely in the well or manually at the surface. Debris  90  typical of that displaced from the drilling riser and BOP during the running of the THRT, SSTT and completion riser (not shown) is indicated on top of, and trapped between, the two wireline plugs  11 ,  12 . The wireline plug pulling tool  80  includes a housing  84  having a diameter which co-acts with the reduced diameter smooth bore  75  to restrict flow of fluid between the outside diameter of the wireline plug pulling tool  80  and the completion riser assembly bore below the reduced diameter smooth bore  75 . It is clear that this flow could be reduced to zero if required by the introduction of seal elements at this location. The wireline plug pulling tool  80  further includes a vertical flow port  83  which extends from, or near to, the bottom wireline plug latch mechanism  86  upward to intersect with horizontal flow ports  82  which exit into the bore of the completion riser assembly above the reduced diameter smooth bore  75 . It can then be seen that pumping fluid down the completion riser assembly from a surface vessel (not shown) would produce a fluid jet downward from the bottom of the wireline plug pulling tool  80 , and that this fluid jet could be used to wash debris from on top of the tubing hanger  18  and the wireline plugs  11 ,  12 . The debris could be carried up and exit out of the choke and kill line  62  or other of the multiple choke and kill lines of BOP  60 . It is clear that this washing could be conducted prior to the landing of the THRT  70  onto the tubing hanger  18 . After the THRT  70  is connected to the tubing hanger and the production stab  71  and/or the sleeve valve  72  of the THRT  70  is shifted to the open position, debris washing may be continued, even though the BOP rams  65  have been closed, sealing the annulus between the THRT-SSTT assembly and the BOP bore  61 , placing the well in a safe (controlled) condition before the wireline plugs  11 ,  12  are pulled. The production stab  71  and sleeve valve  72  may be hydraulically operated cylinders with seals positioned on each end. The stab  71  and/or sleeve  72  may move vertically to enter a mating counter bore to complete a sealed barrier between two cylindrical parts of the tubing hanger running tool  70 , and the riser above the tool  80  in the upward direction and between the tubing hanger running tool  70  and the tubing hanger  18  in the lower direction. Such details regarding hydraulic cylinders are well known to those skilled in the art. 
         [0029]    Referring to  FIG. 3 , a wireline plug pulling tool  80  is shown latched with the wireline plug latch mechanism  86  into the fishneck of the upper wireline plug  12 , in the normal manner, after the obstructing debris has been washed away. The surface wireline unit latch mechanism  86  has been latched into the plug pulling tool fishneck  81  in a similar manner. Standard wireline jarring and pulling operations have been conducted to shift a valve closing the horizontal flow ports  82  of the wireline plug pulling tool  80 . Clearly other valve devices such as a check valve could also be used. The completion riser system above the smooth, or seal, bore  75  is automatically filled with seawater, or other fluid such as fresh water, which is present in the drilling riser, as the completion riser system is run. The choke and kill line  62  provides communication between the BOP bore below the rams  65  and a surface vessel (not shown) are flushed clean and filled with completion fluid of the correct weight to balance the bottom hole pressure of the well. The two valves  64  are opened and the hydrostatic pressure of the completion fluid is seen from under the BOP rams  65  and the smooth, or seal, bore  75  and on top of the upper wireline plug  12 . If the plug is free, not wedged or stuck in the bore of the tubing hanger  18 , and the area under the plug can be vented or pressurized through the workover control system as intended, then the plug can be pulled using the surface wireline unit as normal. The hydrostatic pressure from the completion fluid in the choke and kill line  62  will be higher than the hydrostatic pressure from the completion riser. This pressure differential can be increased up to the limit of the system by increasing the pressure down the choke and kill line  62 . Because the wireline plug pulling tool  80  includes a diameter  84  which co-acts with the reduced diameter smooth bore  75  and this diameter is larger than the outside diameter of the wireline plug  12 , the pressure from the choke and kill line  62  will produce an upward load on the wireline plug pulling tool  80  and the wireline plug  12  attached to it. The higher specific gravity of the completion fluid in the choke and kill line is the less load is required from the surface wireline unit. This is exactly opposite to the normal situation and beneficial for deep-water applications with low wellhead pressures. The wireline plug pulling tool  80  and the upper wireline plug are retrieved to the surface vessel (not shown) using the surface wireline unit as normal. The wireline plug pulling tool  80 , adjusted in length, is lowered back into position to wash the debris from on top of and retrieve the lower wireline plug  11  in the same procedure as used for the upper plug  12 . After the plugs are retrieved, the production stab  71  and/or the sleeve valve  72  of the THRT  70  is shifted to the closed position and well completion or workover operations may be continued. 
         [0030]    Referring to  FIG. 4 , a wireline plug pulling tool  80  is shown latched with the wireline plug latch mechanism  86  into the fishneck of the upper wireline plug  12 , in the normal manner, after the obstructing debris has been washed away. The wireline plug pulling tool  80  is suspended on a shoulder  85  mating with the landing shoulder  74 , which is part of the THRT  70 , specifically incorporated into the sleeve valve  72  of the THRT. When configured in this manner, the wireline plug  12  is subject to the combined pulling loads of the surface wireline unit, the upward load on the wireline plug pulling tool  80  produced by the pressure from the choke and kill line  62  and the upward load from the sleeve valve  72  actuator mechanism. It is clear that his upward loading landing shoulder mechanism could be built into any component of the completion riser, SSTT or THRT. 
         [0031]    Referring to  FIG. 5 , a wireline plug pulling tool  80  is shown latched with the wireline plug latch mechanism  86  into the fishneck of the upper wireline plug  12 , in the normal manner, after the obstructing debris has been washed away. The wireline plug pulling tool  80  diameter  84 , which co-acts with the reduced diameter smooth bore  75  to restrict or seal flow of fluid between the outside diameter of the wireline plug pulling tool, has been replaced in this variation of the invention by packer assembly  79  which increases in diameter to seal in the completion riser assembly bore. This allows the tool to wash debris and provides force to pull the plugs by supplying pressure from the choke and kill line  62 . All other operations are as described above. 
         [0032]    Referring to  FIG. 6 , a wireline plug pulling tool  80  is shown latched with the wireline plug latch mechanism  86  into the fishneck of the upper wireline plug  12 , in the normal manner, after the obstructing debris has been washed away. The surface wireline unit has been replaced in this variation of the invention by a pipeline pigging element  87 . The forces to pull the plugs are supplied by pressure from the choke and kill line  62 . The standard wireline running and pulling functions may be replaced by flow from above or from below the pipeline pigging element  87 , thus driving the wireline plug pulling tool  80 , and when latched to it, the wireline plug, up and down the completion riser. All other operations are as described above. 
         [0033]    Referring to  FIG. 7 , a wireline plug pulling tool  80  is shown latched with the wireline plug latch mechanism  86  into the fishneck of the upper wireline plug  12 , in the normal manner, after the obstructing debris has been washed away. The completion riser, SSTT and THRT has been replaced in this variation of the invention by a drill pipe handling string attached to a simple tubular housing  40 . The housing or the drill pipe handling string may include one or more valves as safety closure devices  47 . This housing includes a smooth, or seal, bore  45 , which is larger than the wireline plugs  11 ,  12  and smaller in diameter than the housing bore below the smooth, or seal, bore  45 . A landing shoulder  44  is provided above or below the reduced bore  45 . In addition, the tubular housing comprises an internal bore  46  or production port, and stab  41 , which connects to the production bore  26  of the tubing hanger  18 . The forces to pull the plugs are supplied by pressure from the choke and kill line  62  and an additional, or replacement, force by applying tension to the drill pipe handling string. The complete assembly, including the wireline plug  12  or  11  latched to the plug pulling tool  80 , is retrieved using the drill pipe handling string through the drilling riser after the BOP rams  65  have been retracted. All other operations are as described above. 
         [0034]    Referring to  FIG. 8 , a wireline plug pulling tool  80  is shown latched with the wireline plug latch mechanism  86  into the fishneck of the upper wireline plug  12 , in the normal manner, after the obstructing debris has been washed away. The completion riser, SSTT and THRT has been replaced in this variation of the invention by a wireline plug pulling tool guide tubular housing  40 . The housing, or assemblies attached to it, may include one or more valves as safety closure devices  47 . This housing includes a smooth, or seal, bore  45 , which is larger than the wireline plugs  11 ,  12  and smaller in diameter than the housing bore below the smooth, or seal, bore  45 . A landing shoulder  44  is provided above or below the reduced bore  45 . In addition, the tubular housing comprises an internal bore  46  or production port, and stab  41 , which connects to the production bore  26  of the tubing hanger  18 . The forces to pull the plugs are supplied by pressure from the choke and kill line  62  and an additional, or replacement, force by applying pressure from the choke and kill line  67  under BOP rams  69 , or other sealing devices of the BOP. The diameter of the tubular housing  40  is larger at this position than the BOP ram  65  sealing position. The pressure from the choke and kill line  67  therefore produces an upward load on the tubular housing  40  which in turn is transmitted through landing shoulder  44  and plug pulling tool shoulder  85  to pull the wireline plug  12 . The complete assembly, including the wireline plug  12  or  11  latched to the plug pulling tool  80 , may be retrieved through the drilling riser, after the BOP rams  65  and  69  have been retracted, using a drill pipe handling string which connects to the tubular housing  40 . Alternatively, the wireline plug pulling tool  80  including the wireline plug  12  or  11  latched to the plug pulling tool may be retrieved independently to the surface vessel (not shown) using the surface wireline unit as normal. All other operations are as described above. 
         [0035]    It should be apparent to those skilled in the art that changes can be made without departing from the scope of the invention. For example, a variety of tubing hanger running tools may be employed. 
         [0036]    The particular embodiments disclosed above are illustrative only, as the invention may be modified and practiced in different but equivalent manners apparent to those skilled in the art having the benefit of the teachings herein. For example, the process steps set forth above may be performed in a different order. Furthermore, no limitations are intended to the details of construction or design herein shown, other than as described in the claims below. It is therefore evident that the particular embodiments disclosed above may be altered or modified and all such variations are considered within the scope and spirit of the invention. Accordingly, the protection sought herein is as set forth in the claims below.