Abstract:
A well completion system includes a wellhead, a control line assembly for use in completions that is mounted to the wellhead, and a tubing hanger. The control line assembly includes a cylinder, a main housing assembly, a passage and a metal-to-metal seal. A split lockout ring provides a positive lock to the passage. Control lines enter the tubing hanger and exit via the wellhead. This arrangement on the wellhead provides sufficient height and clearance to allow for the installation of a plurality of control lines.

Description:
FIELD OF THE INVENTION 
       [0001]    This invention relates to oilfield completion systems and, in particular, to a wellhead completion system having a metal-to-metal sealing arrangement for control lines installed on a surface wellhead. 
       BACKGROUND OF THE INVENTION 
       [0002]    For many surface and subsea oil and gas wells, a series of pipes, fittings, valves, and gauges are used on a wellhead to control the flow and achieve well completion. A Christmas or production tree is generally attached to the wellhead and the pipes, fittings, valves and gauges are typically routed and connected to the tree. One, or a plurality of, penetrators or stems, may be installed in a Christmas tree to engage components installed within the wellhead, such as a tubing hanger. The penetrators may be horizontal, vertical, or at other angles, and allow downhole control lines, such as electrical and/or hydraulic, to be routed through the tree and tubing hanger sidewalls and be routed down to components below the wellhead. 
         [0003]    Subsea horizontal tree tubing hangers generally utilize a sealing arrangement for control lines that rely on the weight of completion tubing to activate the device sealing mechanism. On conventional surface wellhead applications, however, there is insufficient space available on most completions to incorporate this sealing arrangement 
         [0004]    Well completions are now using an increasing number of downhole control lines with some operators now requesting up to eleven separate control lines. As explained above, the conventional method of exiting a plurality of control lines through the wellhead usually requires that the control line pass through a tubing hanger in a continuous manner and then exit through the wellhead body. However, large numbers of control lines make this conventional exit arrangement complex and difficult to complete within the limited space available in the wellhead upper bowl area. Fitting multiple control lines in the limited space currently available is difficult and labor intensive, with control lines frequently bent in awkward directions with some having to physically cross over others. Control lines are thus frequently damaged. Thus, little space on this particular completion arrangement is left to provide “spare” length on the control line. 
         [0005]    Further, if any problems are encountered during the control line termination phase through the wellhead, it may be necessary to pull the completion, which is an expensive and time-consuming exercise involving significant rig down-time. 
         [0006]    A need exists for a technique to allow sufficient clearance for a plurality of downhole control lines at a well. 
       SUMMARY OF THE INVENTION 
       [0007]    In an embodiment of the invention, a well completion includes a wellhead, a control line assembly, and a tubing hanger. The wellhead may have a generally cylindrical body with a bore. The control line assembly may include a cylinder and a main housing assembly with a flange with a bolt pattern at one end for mounting to the wellhead body via bolts. The control line assembly may further include a passage and a metal-to-metal seal. The passage may be a tube or stem within the cylinder that has an inlet at an exterior end and extends into the wellhead bore at another end. A split lockout ring provides a positive lock to the passage. A plurality of control line assemblies may be mounted to the wellhead. The well completion described herein may also be used in production casing hangers to run control lines down through a production annulus. 
         [0008]    The tubing hanger may have a plurality of vertical passages formed in a sidewall of the hanger that communicates with well components, such as valves or instrumentation devices, within the well and below the tubing hanger. Further, a plurality of radial passages communicate with the vertical passages at one end and communicate radially with an outer surface of the tubing hanger. The tubing hanger may be landed within the bore of the wellhead and oriented such that the radial passages in the tubing hanger align with each of the passages of each of the control line assemblies. 
         [0009]    This arrangement on the wellhead of the control line assemblies advantageously provides sufficient height and clearance to allow for the installation of a plurality of control lines entering into the tubing hanger and exiting from the wellhead. 
         [0010]    This invention provides several additional advantages. The invention advantageously overcomes the problem of bending and fitting multiple control lines in the limited space available by moving the exit point down to the main wellhead body and creates multiple control line entry points on the tubing hanger body with a minimal height increase. The multiple control lines can be accommodated in a “single band” around the tubing hanger and wellhead body thereby minimizing any height impact. In addition, safety for personnel is improved by this invention given that work around an open well, which may involve working underneath suspended BOP stacks, is minimized. From an operational safety standpoint, hydraulic control line communication can be advantageously achieved immediately after the tubing hanger has landed in the wellhead without the need to break the BOP stack and thereby maintaining complete well control. Further, as the mating stem seal surface on the tubing hanger body is below the main outer diameter of tubing hanger body, seal surface is protected from damage during tubing hanger installation operations through a BOP stack. This invention further reduces risk of control line damage and reduces the risk of the cost and downtime related to pulling a completion. Further, the invention provides metal-to-metal sealing, which is particularly suitable for critical and high pressure/high temperature applications, is tamper-proof, and reduces rig down time during the control line termination process. Further, the invention provides immediate communication with downhole hydraulic lines once the tubing hanger is landed. The control line assemblies can also be retrofitted onto an existing wellhead as required by the number of downhole control lines required. The invention also provides a lower cost alternative to comparable third-party exit valve arrangements. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0011]      FIG. 1 , is a perspective view of an embodiment of a wellhead, in accordance with the invention; 
           [0012]      FIG. 2 , is a top view of the wellhead of  FIG. 1 ; 
           [0013]      FIG. 3 , is a partial sectional view of an embodiment of a control line assembly mounted to the wellhead, in accordance with the invention; and 
           [0014]      FIG. 3A , is an enlarged view of a portion of  FIG. 3 , in accordance with the invention. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0015]      FIG. 1  shows a perspective view of an embodiment of a generally cylindrical wellhead  10  having a bore  12 , that may be installed on a surface or subsea well. In this embodiment, the wellhead  10  further has a body or wellhead body  14  with a sidewall  16 . The sidewall may have a radial thickness defined generally by a difference between an outer surface of the body  14  and an upper connection  18 . The upper connection  18  shown has a generally cylindrical shape, although the upper connection can take the form of a flange, and extends upward from the body  14  of the wellhead  10 . 
         [0016]    Continuing to refer to  FIG. 1  and also  FIG. 2 , a control line assembly  24 , which may be one of a plurality of assemblies, is mounted to the body  14  of the wellhead  10  via bolts  26 . The bolts  26  pass through bolt passages (not shown) in a flange  28  on a mounting end of the control line assembly  24  and further engage corresponding bolt passages (not shown) formed in the body  14  of the wellhead  10 . The flange  28  of the control assembly  24  is received by a recess  30  formed on the outer surface of the wellhead body  14 . The flange  28  may be a standard API flange or some form of compact flange design. A seal ring  29  ( FIG. 3 ) may be located between the flange  28  and the wellhead body  14  to effect a seal. In the embodiment of  FIGS. 1 and 2 , the control line assembly  24  extends radially outward from the wellhead  10  and horizontally. However, the assembly  24  could also extend outward at an angle from horizontal. The number of control line assemblies  24  and other connections may vary with the requirements of the well completion. The control line assembly  24  and instrumental signal port  32  will be explained further below. 
         [0017]    Referring to  FIG. 3 , a portion of the wellhead  10  having the control line assembly  24  is illustrated in side sectional view. The control line assembly  24  has an outer cylinder  40  fitted with an end cap  41  to define, in part, a hydraulic cylinder. A penetrator or stem  42  having an axial passage  43  with inner diameter is located within the cylinder  40  and has an indicator or recess  44  at an outer end  46 . The indicator  44  is formed on a circumferential periphery of the stem  42  and indicates when the stem  42  is properly installed within the wellhead body  14 . The indicator  44  is on a portion of the stem  42  that projects past the end cap  41 . The stem  42  has a control line inlet  48  at the outer end  46  that may allow connection to control sources such as a hydraulic supply. A horizontal passage  50  traverses the wellhead sidewall  16  to communicate the outer surface of the wellhead body  14  with the bore  12 . Horizontal passage  50  allows a penetrating end  52  of the stem  42  to pass through wellhead sidewall  14 . In this embodiment, passage  43  increases to a diameter  54  within the penetrating end  52  of the stem  42 . 
         [0018]    Continuing to refer to  FIG. 3 , the penetrating end  52  of stem  42  has a nose arrangement  60  terminating at penetrating end  52 . Nose arrangement  60  has a wave-like profile  61  which is located within horizontal passage  50 . The nose arrangement  60  of the stem  42  corresponds with bore  12  of the wellhead  10  and interfaces with an exterior surface  62  of a tubing hanger  64  shown landed within the wellhead  10 . When energized against the tubing hanger  64  interface, the nose arrangement  60  creates a metal-to-metal seal. In this embodiment, tubing hanger  64  is properly aligned with the control line assembly  24  via a key  66  located at a lower portion of tubing hanger  64 . The key  64  is outwardly biased by at least one spring  68 . Key  66  is retracted until the key is received by a corresponding recess  70  formed in wellhead bore  12 . Other types of alignment mechanisms may also be utilized. When tubing hanger  64  is properly aligned within the wellhead  10 , a horizontal hanger passage  72  registers with nose arrangement  60  to establish communication with passage  43  of stem  42 . An annular metal seal  74  is located within a seat  76  formed at nose arrangement  60  to seal at interface formed by nose arrangement and horizontal hanger passage  72 . In this embodiment, horizontal passage  72  intersectingly communicates with a vertical hanger passage  80 . Vertical hanger passage  80  further communicates with a lower surface  82  of tubing hanger  64  to allow communication with a line  84  that may connect to an inlet  86  located at lower end of vertical hanger passage. Line  84  may serve various types of components located below the hanger  64 . 
         [0019]    Continuing to refer to  FIG. 3 , a hydraulic piston  100  in this embodiment is formed integral with the stem  42  and allows the stem to reciprocate axially within a distance defined by end cap  41  and a stop  102  that projects radially inward from cylinder  40 . As significant force is required to activate the nose arrangement  60  and set the metal-to-metal seal at the tubing hanger  64 , a chamber  104  may be pressurized to deliver a distributed force to a back face of piston  100  to move piston, and thus stem  42 , forward into sealing engagement with tubing hanger  64 . The chamber defined by the cylinder  40 , end cap  41 , stop  102 , and hydraulic piston  100 . Chamber  104  may also be pressurized on front face of piston  100  by an external source (not shown) to cause piston to retract, allowing retrieval of the tubing hanger  64 . When the stem  42  is in a fully engaged position with tubing hanger  64 , indicator mark  44  on the outer end  46  provides visual indication to the operator that the metal-to-metal seal is set. When the stem  42  is not in engaged position with tubing hanger  64 , indicator mark  44  on the outer end  46  will be recessed within end cap  41  and thus not visible. 
         [0020]    Continuing to refer to  FIG. 3 , once stem  42  is set against tubing hanger  64 , the stem  42  may be positively locked in place by a split lockout ring  106  to thereby prevent loss of sealing. The split lockout ring  106  has a toothed inner profile  108  and a tapered rear surface  110 . The toothed inner profile  108  lockingly engages a corresponding mating profile  112  formed on an outer surface of stem  42 . Mating profile  112  may also have a toothed profile. Tooth profiles on the split lockout ring  106  and mating profile  112  may have varying depths depending on the application. The split lockout ring  106  is held off stem  42  by a hydraulic lockout piston  114  while stem  42  is energized and set. This hydraulic locking mechanism acts as a safety measure in that there are no external components which can be tampered with or accidentally activated to unset the locking mechanism. An operator must physically connect a hydraulic supply to an inlet port (not shown) on the control line assembly  24  and apply pressure. Once stem  42  is set against the tubing hanger  64 , pressure is released from the lockout piston  114  and the split lockout ring  106  is then driven down onto mating tooth profile  112  by a wave spring  116  to positively lock the stem  42  in place. Wave spring  116  is located at one end to split lockout ring  106  and at a second end to an internal housing  118  concentric with the stem  42 . Wave spring  116  has a flat face at each end to engage mating component faces. 
         [0021]    Continuing to refer to  FIG. 3 , a metal-to-metal seal  130  may also be effected between stem  42  and a main housing assembly  134  and a flexible metal seal lip  135  which sealingly engages outer surface of the stem as shown in  FIG. 3A . The seal lip  135  is in interference contact with the stem  42 , with this sealing arrangement further enhanced by any pressure present in the wellhead bore  12 . An inside surface of the lip  135  may have a plurality of sealing lands or raised faces which initially form an interference seal and then progressively increases the sealing contact as the pressure in the wellhead bore  12  increases. The seal lip  135  partially defines an inner dynamic seal  137  ( FIG. 3A ). This is achieved by a metal seal ring  132  concentric with stem  42  that sealingly engages the main housing assembly  134  to form outer static seal  139  ( FIG. 3A ). In this embodiment, a stem seal area  136  of outer surface of stem  42  may be have a tungsten carbide coating so the stem seal area  136  can withstand forces applied by the flexible metal seal lip  135  that may result in galling between the stem  42  and flexible lip. Metal-to-metal seal  130  of stem  42  with main housing assembly  134  and metal-to-metal seal of nose arrangement  60  with tubing hanger  64  may both be verified via a test port (not shown) on the main housing assembly  134 . The outer static seal  139  utilizes a metal-to-metal seal ring profile which effects a seal by elastic deformation of a seal lip opposite the metal seal lip  135  when made-up to the main housing assembly  134 . In this embodiment, the metal-to-metal seal assembly is installed in the main housing body  134  and then the internal housing  118  is threaded in with this process energizing the outer static seal  139 . The stem  42  is then inserted through the inner dynamic seal  135  followed by remaining components, including  116  and  106 . 
         [0022]    In one example, during installation of the control line assembly  24 , the control line assembly is mounted to wellhead body  14  such that the penetrating end  52  of the stem  42  enters the horizontal passage  50  formed in the wellhead sidewall  16 . To energize and set the metal-to-metal seal between the nose arrangement  60  and previously landed tubing hanger  64  via annular metal seal  74 , chamber  104  is pressurized at a front face of piston  100  to move piston, and thus stem  42 , forward. Sufficient force is generated by piston  100  to force metal seal  74  into sealing engagement with tubing hanger  64 . To retract stem  42  and allow retrieval of tubing hanger  64 , chamber  104  may be depressurized or pressurized on front face of piston  100  to cause piston to retract as a force exerted by the wave spring  116  drives the split lockout ring  106  and lockout piston  114  back to the original, deenergized position. When the stem  42  is in a fully engaged position with tubing hanger  64 , indicator mark  44  on the outer end  46  provides visual indication to the operator that the metal-to-metal seal at nose arrangement  60  is set. Once stem  42  is set against tubing hanger  64 , the stem is positively locked in place by the split lockout ring  106  to thereby prevent loss of sealing at the nose arrangement  60 . During the setting operation the split lockout ring  106  is held off stem  42  by hydraulic lockout piston  114 . The lockout piston  114  is depressurized once stem  42  is set. Wave spring  116  then forces the split lockout ring  106  to move forward and the toothed inner profile  108  of lockout ring then lockingly engages corresponding mating profile  112  formed on outer surface of stem  42 . Metal-to-metal seal  130  may also be effected between stem  42  and main housing assembly  134  when the stem is locked in place. 
         [0023]    This written description uses examples to disclose the invention, including the best mode, and also to enable any person skilled in the art to practice the invention, including making and using any devices or systems and performing any incorporated methods. These embodiments are not intended to limit the scope of the invention. The patentable scope of the invention is defined by the claims, and may include other examples that occur to those skilled in the art. Such other examples are intended to be within the scope of the claims if they have structural elements that do not differ from the literal language of the claims, or if they include equivalent structural elements with insubstantial differences from the literal language of the claims.