Patent Publication Number: US-2018038190-A1

Title: Method and apparatus to effect injection of fluids into a subsea horizontal tree

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     The present application claims priority from U.S. Provisional Patent Application Ser. No. 62/371,953, filed on Aug. 8, 2016. 
    
    
     STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT 
     Not applicable. 
     NAMES OF THE PARTIES TO A JOINT RESEARCH AGREEMENT 
     Not applicable. 
     INCORPORATION-BY-REFERENCE OF MATERIALS SUBMITTED ON A COMPACT DISC 
     Not applicable. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to subsea horizontal trees. More particularly, the present invention relates to systems for injecting fluids into such a subsea horizontal trees. Additionally, the present invention relates to apparatus for maintaining the dual barrier system within the subsea horizontal tree. 
     2. Description of Related Art Including Information Disclosed Under 37 CFR 1.97 and 37 CFR 1.98 
     Conventional wellhead systems include a wellhead housing mounted on the upper end of a subsurface casing string extending into the wellbore. A riser and blowout preventer are then installed. During the drilling procedure, the blowout preventer is installed above the wellhead housing (i.e. a casing head) to provide pressure control as casing is installed, with each casing string having a hanger on its upper end for landing on a shoulder within the wellhead housing. Upon completion of this process, the blowout preventer is replaced by a Christmas tree installed above the wellhead housing, with the tree having a valve to enable the oil or gas to be produced and directly into flowlines for transportation to a desired facility. 
     The horizontal Christmas tree replaces the conventional casing and tubing heads of the generally vertical Christmas trees. The horizontal Christmas tree comprises a spool with a generally horizontal through port mounted above and in axial alignment with a horizontal through port in the wellhead housing. The hangers for the casing strings are supported one above the other within the bore of the wellhead housing, and the tubing hanger for the production or tubing string is supported in the bore of the spool to suspend the production string within the casing strings. 
     The vertical bore through the tubing hanger of a horizontal tree may be closed by a wire line tool to connect the production fluid through aligned side ports (generally horizontal through ports) in the hanger and spool for recovery and delivery of production fluid to a suitable location. A redundant seal may be provided by well cap installed in the tree above the tubing hanger, with the vertical bore aligned with that of the tubing string closed by a crown plug. 
     Typical horizontal subsea trees contain two independently installed and tested crown plug assemblies. These crown plug assemblies can be located together in an extended tubing hanger or separately in the tubing hanger and an independently installed internal tree. These crown plugs create a dual barrier system that isolates the main production flow path of the tubing hanger and the environment. 
     Typical horizontal subsea trees also include a small bore flow path that connects the main upper mandrel of the tree to the annulus portion of the subsea tree. There is typically one or two valves located in this flow path so as to isolate the annulus portion of the tree to the environment. The annulus flow path enters the mandrel either above both crown plugs or sometimes between the crown plugs. The annulus portion of the tree is connected to the production portion of the tree through cross-over piping and valving. 
     In order to facilitate injection of chemicals into horizontal tree, the crown plugs must be removed to gain access to the production flow path. In some cases, fluid may be pumped into the annulus portion of the tree directly from the upper mandrel into the production flow path through the cross-over piping without removing the crown plug. In the event that the crown plug is removed to facilitate injection, the proper well control and barrier philosophy must be put into place to prevent spills to the environment. 
     For certain horizontal subsea trees that require more continuous injection of fluids, it would be beneficial to remove the upper crown plug in order to expose the annulus flow path. As such, a device is required so as to maintain the required dual barriers in order to provide the required secondary metal-to-metal barrier, provide the necessary intervention to isolate the upper mandrel of the tree in order to allow injection of fluids in the testing of the seals, and to provide the required hub connection to allow for the connection of hose/pipe/equipment to facilitate injection of fluids into the tree cap and thus into the upper mandrel of the subsea tree. 
     In the past, various patents have issued relating to subsea trees. For example, U.S. Pat. No. 5,992,526, issued on Nov. 30, 1999 to Cunningham et al., shows a deployable tree cap for deployment on a subsea production hub of a subsea tree. The tree cap has a lightweight body with parallel planar sides and including suitable openings in slots for mounting the various operating elements. A seal plate structure includes a piston connected to a seal plate having a pair of downwardly projecting tubular steel members for fitting within the production bore and annulus bore of the tree hub in a sealed landed position. Fluid pressure is applied to a fluid line to urge a piston and seal plate downwardly into a sealing landed position. 
     U.S. Pat. No. 7,677,319, issued on Mar. 16, 2010 to D. Baskett, discloses a retrievable tree cap for use in a subsea tree. The tree cap is installed and retrieved using a remotely operated vehicle. Hydraulic pressure is used to lock the tree cap onto the subsea tree and to set the tree cap seals. The tree cap is locked onto the subsea tree before setting the seals within the concentric bore. The tree cap includes a locking means that engages a profile within the subsea tree regardless of the radial orientation of the tree cap. The tree cap is used to hydraulically isolate an annulus bore from the production bore of the subsea tree. The tree cap provides for the injection of a corrosion inhibitor within a cavity of the tree cap. 
     U.S. Pat. No. 8,087,465, issued on Jan. 3, 2012 to Huang et al., provides a locking tree cap for use in a subsea tree. The tree cap is installed and retrieved using a remotely operated vehicle. The tree cap includes the flexible collet fingers the lock the tree cap to a tree spool. The deflected collet fingers are adapted to extend into the recess of the tree spool when the tree cap has been landed on the tree spool. 
     U.S. Pat. No. 8,230,928, issued on Jul. 31, 2012 the Cuiper et al., teaches a low-profile internal tree cap having a running configuration and a latched configuration to be selectively secured to a tree spool. The tree cap includes an inner sleeve movable between upper and lower positions. The movement of the inner sleeve to the lower position simultaneously engages a locking profile within the tree spool and energizes a sealing element around the exterior of the tree. 
     U.S. Patent Application Publication No. 2014/0060849, published on Mar. 6, 2014 to Pathak et al., discloses a cap system for use on subsea equipment, including a horizontal tree. The cap system includes a cap assembly that has the flexibility of installation and retrieval. The cap assembly includes a debris cap assembly in engagement with the cap assembly. The cap assembly interface has to provide the ability to inject in bleed fluids into the main bore and an annulus bore of the subsea tree independently and without removal of the debris cap assembly. 
     Canadian Patent No. 2428165, issued on Aug. 12, 2008 to I. Donald, teaches a flow diverter for use through a tree cap. The flow diverter assembly has a flow diverter to divert fluids flowing through the production bore of the tree from a first portion of the production bore to the cap, and to diverge the fluids back from the cap to a second portion of the production bore for recovery therefrom via an outlet. The flow diverter is detachable from the cap to enable insertion of the flow diverter through the cap. 
     It is an object of the present invention to provide a method and apparatus which maintains dual barriers against the release of fluids to the environment. 
     It is another object of the present invention to provide a method and apparatus that maintains a secondary metal-to-metal barrier on the subsea tree. 
     It is another object of the present invention provide a method and apparatus that effects the injection of fluids and the testing of seals within the subsea horizontal tree. 
     It is another object of the present invention to provide a method and apparatus that facilitates connection of the tree cap to external piping in order to inject fluids into the subsea tree. 
     These and other objects and advantages of the present invention will become apparent from a reading of the attached specification and appended claims. 
     BRIEF SUMMARY OF THE INVENTION 
     The present invention is a fluid injection tree cap that comprises a body for attachment to a mandrel of the subsea tree. A bore extends through the body so as to have one end opening at the top of the body and an opposite end opening into the mandrel of the subsea tree. An isolation valve is provided on the body or in cooperation with the bore of the body in order to open or close the bore. This isolation valve is, in particular, positioned above the body of the tree cap. A hub is adapted to allow for the connection of piping on the side of the isolation valve opposite the body. 
     The present invention can further include the horizontal subsea tree. In this subsea tree, one crown plug has been removed. The subsea tree has the mandrel at the upper end thereof. A small bore flow path extends from the annulus of the subsea tree to the mandrel. A tubing hanger is located in the annulus. A lower connector is provided on the subsea tree in order to connect the subsea tree to the wellhead. Valving is provided on the annulus flow paths and on the production flow paths of the subsea tree in order to direct fluids from the bore of the tree cap to an annulus of the well or to production tubing or to the subsea tree. The fluid injection tree cap is in a metal-to-metal seal with the mandrel of the subsea tree. 
     The present invention is also a method for effecting injection of fluids into a subsea horizontal tree. This method includes the steps of: (1) affixing a fluid injection tree cap onto a mandrel of the subsea horizontal subsea tree; (2) removing a crown plug from the subsea tree so as to expose an annulus flow path; (3) connecting the tree cap to a fluid-delivering pipe; and (4) opening a valve so that fluid from the piping flows through a bore in the body of the tree cap and into the upper mandrel of the tree and into the annulus portion of the subsea tree. In the method of the present invention, fluid can then be directed either into the annulus of the well bore or into the production side of the tree. 
     In this method of the present invention, an isolation valve is provided between a hub that is connected to the fluid-delivering pipe and the tree. In this method, the isolation valve is opened so as to allow fluid to flow from the pipe into the bore of the tree cap. 
    
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
         FIG. 1  is a schematic illustration showing the application of the tree cap of the present invention onto a horizontal subsea tree. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring to  FIG. 1 , there is shown the apparatus  10  of the present invention for effecting injection of fluids into a subsea horizontal tree  12 . In particular, the tree cap  14  is applied onto the upper mandrel  16  of the subsea tree  12 . The subsea tree  16  has a lower connector  18  that is secured to the wellhead  20 . A tubing hanger  22  is positioned within the bore  24  of the hanger portion of the subsea tree  12 . 
     The tree cap  14  includes a body  26  that has a bore  28  extending therethrough. In the preferred embodiment the present invention, this bore is a two inch bore. However, the bore can be larger or smaller. An isolation valve  30  is connected to the bore  28 . The isolation valve  30  can be manually or remotely operated. For example, an ROV actuator  32  can be used with the isolation valve  30  so as to open or close the isolation valve. A hub  34  is connected to the bore  28  and located on a side of the isolation valve  30  opposite to the body  26 . The hub  34  allows the bore  28  to be connected to an injection system, such as a fluid-delivering pipe. The cap  14  also includes a wellhead-type of connector  36  or similar device that locks onto the upper mandrel  16  of the horizontal subsea tree  12  and provides a metal-to-metal seal. 
     In the subsea horizontal subsea tree  12 , there is illustrated in broken lines a crown plug  38 . This illustration is to show the location of the crown plug  38  prior to removal. In actual operation, when the tree cap  14  is positioned on the mandrel  16 , the crown plug  38  is removed so as to expose the annulus flow path of the subsea tree  12 . 
     The subsea tree  12  includes an annulus flow path  40  therein. An annulus workover valve  42  extends outwardly of the subsea tree  12  and allows fluid flow into the annulus. The annulus workover valve  42  can be controlled or actuated by a remotely operated vehicle or can be actuated from a surface location. The annulus workover valve  42  allows workover fluids to be introduced into the apparatus  10 . The annulus master valve  44  is connected to the annulus and extends to the bore  28  of the subsea tree  12  so as to allow annulus fluids to be delivered into the bore. An annulus auxiliary valve  46  is also provided so as to extend to the bore  24 . A line  48  will extend from the annulus workover valve  42  and from the annulus so as to pass to the bore  28 . 
     Production fluids can flow through line  50  from the wellhead  20 , through the connector  18 , through the hanger  22  and toward a series of production valves. The first valve  52  is the production master valve so as to control the flow of production fluids outwardly of the subsea tree  12 . A production wing valve  54  is connected in line with the master production valve  52 . A crossover valve  56  allows fluids from the bore  28  or from the annulus  40  to pass therethrough and into the production fluids flowing along line  50 . A production isolation valve  58  is positioned along line  60  so as to stop the flow of fluids through the line  50 . A hub  62  is formed at the end of the line so as to allow the production line  50  to ultimately be connected to piping so that production fluids can be ultimately delivered to a surface location. 
     Typical horizontal subsea trees contain two independent crown plugs in the bore  24  so as to isolate the main production flow path from the environment. However, for certain horizontal subsea trees that require more continuous injection of fluids, it would be beneficial to remove the upper crown plug  38  so as to expose the annulus flow path. In order to maintain the required dual barriers, the externally-fitted fluid injection tree cap  14  is installed with the necessary valving and connection points. This fluid injection tree cap  14  provides the required secondary metal-to-metal barrier by this locking connection with the mandrel  16 . It also provides the necessary intervention valves to isolate the upper mandrel of the tree. This effects injection of fluids in the testing of the seals. The tree cap  14  also provides the required hub connection system so as to allow for the connection of a hose/pipe/equipment or to facilitate injection of fluids into the tree cap and thus into the upper mandrel of the subsea tree. The fluid injection tree cap  14  can be installed permanently or semi-permanently in order to facilitate a single or routine fluid injection program. 
     In the method of the present invention, fluid injected from the tree cap  14  into the upper mandrel  16  and through the annulus auxiliary valve  46  will flow into the annulus portion of the subsea tree. Fluid can then be directed either into the annulus of the well or into the production side of the tree. 
     The foregoing disclosure and description of the invention is illustrative and explanatory thereof. Various changes in the details of the illustrated construction or in the steps of the method can be made within the scope of the present claims without departing from the spirit of the invention. The present invention should only be limited by the following claims and their legal equivalents.