Patent Publication Number: US-6902005-B2

Title: Tubing annulus communication for vertical flow subsea well

Description:
RELATED APPLICATIONS 
   Applicant claims priority for the invention described herein through a United States provisional patent application titled “Tubing Annulus Communication for Vertical Flow Subsea Well,” having U.S. patent application Ser. No. 60/357,230, which was filed on Feb. 15, 2002, and which is incorporated herein by reference in its entirety. 

   BACKGROUND OF INVENTION 
   1. Field of the Invention 
   This invention relates in general to subsea well production, and in particular to a subsea well that has vertical production passages and tubing annulus communication other than through the tubing hanger. 
   2. Background of the Invention 
   A subsea well that is capable of producing oil or gas will have an outer or low pressure wellhead housing secured to a string of conductor pipe that extends some short depth into the well. An inner or high pressure wellhead housing lands in the outer wellhead housing. The tubular wellhead member is secured to an outer string of casing, which extends through the conductor pipe to a deeper depth into the well. Depending on the particular conditions of the geological strata above the target zone (typically, either an oil or gas producing zone or a fluid injection zone), one or more additional casing strings will extend through the outer string of casing to increasing depths in the well until the well is to the final depth. 
   The last string of casing extends into the well to the final depth, this being the production casing. The strings of casing between the first casing and the production casing are intermediate casing strings. When each string of casing is hung in the wellhead assembly, a cement slurry is flowed through the inside of the casing, out of the bottom of the casing, and back up the outside of the casing to a predetermined point. A tubing hanger typically connects to the wellhead assembly. When a string of production tubing is lowered into the well and supported by the tubing hanger, a tubing annulus is defined between the outer surface of the production tubing and the innermost or production casing. At a lower portion of the production tubing, a seal system or packer is typically connected to the outer surface of the production tubing and the inner surface of the production casing. After the production casing is perforated, well fluids enter the well through the perforations to communicate up the interior of the production tubing to the wellhead. 
   Sometimes it is desirous for a heavy fluid or “kill” fluid to be pumped either through the tubing or from the tubing annulus past the packer so that the operator can stop production from the well before removing the string of production tubing. In situations where the heavy fluid is pumped down the tubing annulus, the packer may be released for allowing fluid to flow below the packer to the interior of the tubing. 
   Additionally, operators desire a means of communicating and monitoring pressure of producing wells in the production tubing annulus. Normally there should be no pressure in the production tubing annulus because the annular space is sealed with the packer. If pressure increased within the production tubing annulus, it would indicate that a leak exists in one of the strings of casing or in the tubing. The leak could be from several places. Regardless of where the leak is coming from, pressure build up in the production tubing annulus could collapse a portion of the production tubing, compromising the structural and pressure integrity of the well. For this reason, operators typically monitor the pressure in the production tubing annulus between the production casing and the production tubing. 
   In one type of wellhead assembly, the tubing hanger has an offset passage through it for communicating with the tubing annulus. In this type, the tubing hanger lands in the wellhead housing or in a tubing spool above the wellhead housing. In small diameter tubing hangers, there may not be enough space for the tubing annulus passage. In another type, the tubing hanger lands in a production tree mounted on the wellhead housing. A bypass passage extends through the tree around the tubing hanger for communicating with the tubing annulus. 
   BRIEF SUMMARY OF THE INVENTION 
   With the foregoing in mind, a subsea wellhead assembly has a tubular wellhead housing or member and a tubing hanger support attached to an upper portion of the wellhead member. A tubing hanger lands on the tubing hanger support. A string of production tubing extends from the tubing hanger to a desired depth. The string of production tubing defines a production tubing annulus, or tubing annulus, around the outer circumference of the tubing. 
   The wellhead assembly also includes a riser assembly that is lands on the wellhead member. The riser assembly is in communication with the string of tubing and extends to a platform at the surface of the sea. Well fluid flows up the interior of the production tubing and through the riser to the platform at the surface. The wellhead assembly also includes a conduit extending alongside the riser. The conduit is in fluid communication with the platform. The wellhead assembly also has a passage or tubing annulus passage extending from the tubing annulus through the tubing hanger support that communicates with the conduit. 
   Preferably, a valve block is also included in the wellhead assembly. The valve block is supported by the tubular wellhead member between the tubing hanger and the riser. The valve block has a passageway that communicates with the interior of the production tubing and the riser so the well fluids flow through the valve block from the well to the platform. The valve block contains at least one valve for regulating the flow of well fluids entering the riser from the well. 
   A portion of the tubing annulus passage extends through the tubing support to a stab receptacle connected on an upper portion of the tubing support. The valve block has another portion of the tubing annulus passage that stabs into the stab receptor on the tubing support or adapter. The valve block portion of the tubing annulus passage extends generally up the axial length of the valve block to a stab receptacle mounted to the upper portion of the valve block. When the riser assembly connects to the rest of the wellhead assembly, a stab stabs into the stab receptacle on the valve block and connects the conduit to the tubing annulus passage. 
   In one of the embodiments, the tubing support is an adapter that lands in the bore of the tubular wellhead member. In this embodiment, the valve block attaches to a grooved profile on the outer surface of the tubular member. In the other embodiments, the tubing support is a tubing spool, and the valve block attaches to a grooved profile on the outer surface of the valve block. The valve block portion of the tubing annulus passages can be a passage extending through the axial length of the valve block, or the combination of a passage through a portion of the valve block and then to a tubular member running alongside the valve block, or a tubular member running alongside through the valve block. In either embodiment, the valve block portion of the tubing annulus passage stabs into the stab receptacle attached to the tubing support. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIGS. 1A and 1B  comprise a vertical sectional view of a subsea well constructed in accordance with this invention. 
       FIGS. 2A and 2B  comprise a partial sectional view of an alternate embodiment of the subsea well of  FIGS. 1A and 1B . 
       FIGS. 3A and 3B  comprise a partial vertical sectional view of a second alternate subsea well constructed in accordance with this invention. 
       FIGS. 4A and 4B  comprise a partial sectional view of a third alternate subsea well constructed in accordance with this invention. 
       FIGS. 5A and 5B  comprise a partial vertical sectional view of a fourth alternate subsea well constructed in accordance with this invention. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   Referring to  FIG. 1B , an outer or low pressure wellhead housing  11  is located at the sea floor. A large diameter pipe or conductor  13  extends into the well to the first depth. An inner or high pressure housing  15  lands in outer wellhead housing  11 . High pressure wellhead housing or tubular wellhead member  15  has a large diameter string of casing  17  that extends into the well to a second depth and is cemented in place. In this well, there are two strings of casing  17  and  19 , each extending to a greater depth. Each string of casing,  19 ,  21  is supported by a casing hanger  23 ,  25 , respectively, within the bore of inner wellhead housing  15 . 
   A string of production tubing  27  extends through the smallest diameter casing  21 . The well will produce fluids through tubing  27 . A production tubing annulus or tubing annulus  29  exists between tubing  27  and the production casing or smallest diameter casing  21 . It is important to monitor the tubing annulus  29  for leakage and also to be able to circulate fluids through tubing annulus  29 . For example, tubing annulus  29  circulation is normally performed when the well is being killed by loading tubing  27  and tubing annulus  29  with a fluid that is heavier than the formation fluid. This invention deals with different techniques for communicating tubing annulus  29  to a production vessel at the surface. 
   A tubing hanger support, or in the first embodiment, a tubing spool  31 , shown in  FIG. 1A and 1B , has a bore  30  and mounts to the upper end or mandrel of wellhead housing  15 . A connector  32  connects tubing spool  31  to an external profile on the mandrel of wellhead housing  15 . Connector  32  is typically hydraulically actuated and may comprise a type using either dogs  34  or a collet (not shown). A tubing hanger  33  lands within bore  30  of tubing spool  31  and supports the string of tubing  27 . Tubing hanger  33  has a single production passage extending through it. Tubing hanger  33  may also have ancillary passages extending through it for communicating with a downhole safety valve, chemical injection and the like. 
   A valve block  35 , which has similarities to a Christmas tree, lands on top of spool  31  in the first embodiment. Valve block  35  is a large tubular member having a vertical production passage  37  extending through it. The outlet of passage  37  for the produced fluids is vertical rather than horizontal as in a conventional Christmas tree. An isolation sleeve  38  on the lower end of production passage  37  communicates passage  37  with the interior of tubing hanger  33  and tubing  27 . A pair of valves  39 ,  41  mounted to valve block  35  serve to open and close production passage  37 . Production passage  37  extends vertically through valve block  35  and delivers production fluid to the interior of a production riser  43  that extends upward to a platform at the surface. Riser  43  connects to valve block  35  by means of a riser connector  45 , which may be of a type utilizing dogs, collets or bolted flange. A surface Christmas tree (not shown) is located on a surface platform and connected to riser  43 . 
   Tubing annulus  29  is in communication with a void space within the bore of wellhead housing  15  surrounding tubing  27 . This void space within the bore of wellhead housing  15  communicates with a similar void space within tubing spool  31 . A tubing annulus passage  47  extends upward a selected distance from the void space within tubing spool  31  parallel to and offset from tubing spool bore  30 . A lateral portion of annulus passage  47  extends outward to an optional ROV (Remote Operator Vehicle) valve  49  on the side of tubing spool  31 . A tubing annulus conduit  50  extends from valve  49  to a lower stab plate  51  mounted around tubing spool  31 . A stab receptacle  52  is positioned at the end of annulus conduit  50  connected to stab plate  51 . In the first embodiment, annulus passage  47  and conduit  50  define a tubing hanger support portion of a tubing annulus passage. 
   A tubing annulus conduit or pipe  53  extends alongside valve block  35 . Conduit  53  is configured to stab into mating stab receptacle  52  in stab plate  51  when valve block  35  lands on tubing spool  31  so that it will communicate with conduit  50 . Tubing annulus conduit  53  is secured to an upper stab plate  55 , which is mounted to valve block  35  near its upper end. A stab receptacle  54  is positioned at the end of annulus conduit  53  connected to stab plate  55 . A conduit  56  extends alongside riser  43  to the surface vessel and has a lower end that stabs into upper receptacle  54  which is in communication with tubing annulus conduit  53 . In the first embodiment, tubing annulus conduit  53  defines a valve block portion of the tubing annulus passage. In the first embodiment, valve block portion and the tubing hanger support portion of the tubing annulus passage allow communication between conduit  56  and production tubing annulus  29 . 
   In operation, the well is first drilled and cased as shown in FIG.  1 B. Then the operator lowers tubing spool  31  and secures tubing spool  31  to the mandrel of wellhead housing  15  by means of connector  32 . Tubing  27  and tubing hanger  33  will be subsequently run, typically on a completion riser (not shown), with tubing hanger  33  landing in tubing spool  31 . The operator may perforate and test the well at that time. The completion riser has a tubing annulus conduit that stabs into stab receptacle  52  on lower stab plate  51  to communicate tubing annulus  29  with the surface vessel via passage  47  and conduit  50 . 
   Then, the operator will remove the completion riser and lower valve block  35  onto the upper end of tubing spool  31 , preferably with production riser  43 . Connector  36  will connect valve block  35  to spool  31 . Prior to running, conduit  56  will be normally stabbed into engagement with the upper end of conduit  53  at upper stab plate  55 . As valve block  35  lands on tubing spool  31 , it will be oriented so that the lower end of conduit  53  will stab into engagement with conduit  50  at stab plate  51 . Once installed, tubing annulus  29  can be monitored at the production platform via passage  47  and conduits  50 ,  53  and  56 . Fluid can also be circulated through tubing annulus  29  by the same flow path. Production fluid flows up tubing  27 , passage  37  and riser  43  to the surface tree on the platform at the surface. 
   If it is necessary to pull tubing hanger  33  and tubing  27 , the operator will install a plug in tubing hanger  33  and close tubing annulus valve  49 . The operator disconnects connector  36  from tubing spool  31  and removes valve block  35 , preferably with production riser  43 . Conduit  53  will release from engagement with conduit  50  at stab plate  51  as valve block  35  is lifted. The operator will connect a drilling riser (not shown) to the mandrel on valve spool  31 . The drilling riser will have an auxiliary line that will stab into stab plate  51  for communication with tubing annulus conduit  50  and tubing annulus passage  47 . Tubing  31  will be pulled through the drilling riser. 
   In the other embodiments, some of the elements which are the same will not be discussed again. In the first alternate embodiment,  FIGS. 2A and 2B , tubing spool  57  has a tubing annulus passage  59  that extends from its lower end to its upper end, rather than to the sidewall as in FIG.  1 A. In this embodiment, annulus passage  59  defines the tubing hanger support portion of the tubing annulus passage. A stab receptacle  60  is positioned at the upper end of annulus passage  59  on an upper surface of tubing spool  57 . A stab  61  is located on the lower end of valve block  62  in communication with a tubing annulus passage  63  located within valve block  62 . When valve block  62  is being landed on tubing spool  57 , it will be oriented to align stab  61  with tubing annulus passage  59 . A check valve  64  is located at the upper end of tubing annulus passage  59 . When stab  61  lands in the upper end of tubing annulus passage  59 , it opens check valve  64 . When valve block  62  is lifted from tubing spool  57 , check valve  64  closes. Alternately, check valve  64  could be a hydraulically actuated valve. 
   Passage  63  leads upward within valve block  62  to an optional ROV actuated valve  65  on its sidewall. A tubing annulus conduit  67  extends upward to a stab plate  69 , which may be the same as stab plate  55  in the first embodiment. A stab receptacle  68  is positioned at the end of annulus conduit  67  connected to stab plate  69 . In the embodiment shown in  FIGS. 2A and 2B , passage  63  and conduit  67  define a valve block portion of the tubing annulus passage. The valve block portion and the tubing hanger support portion of the tubing annulus passage allow communication between conduit  56  and production tubing annulus  29 . In the embodiment of  FIGS. 2A and 2B , the operation is the same as in the first embodiment except there is no lower stab plate such as stab plate  51 . Instead, when valve block  62  lands on tubing spool  57 , tubing annulus communication will be established through stab  61  and check valve  64 . 
   In the embodiment of  FIGS. 3A and 3B , tubing spool  71  is configured the same as tubing spool  57  (FIG.  2 B), having a tubing annulus passage  73  that extends completely through from the lower end to the upper end. In this embodiment, annulus passage  73  defines the tubing hanger support portion of the tubing annulus passage. A stab receptacle  74  is positioned at the upper end of annulus passage  73  on an upper surface of tubing spool  71 . Alternately, tubing spool  71  could be configured as tubing spool  31  of FIG.  1 A. In the embodiment of  FIGS. 3A and 3B , a stab  75  stabs into stab receptacle  74  to connect tubing annulus passage  73  with a tubing annulus passage  79  in valve block  77 . Tubing annulus passage  73  has a check valve at its upper end. Tubing annulus passage  79  extends upward to a dual valve assembly comprising valves  81 ,  82 . Tubing annulus passage  79  leads to valve  81 . A crossover passage  83  leads within valve block  77  from vertical production passage  85  to valve  82 . Both valves  81 ,  82  selectively open and close to a tubing annulus conduit  87 , which extends externally of valve block  77  to a stab plate  89 . Stab plate  89  is mounted to valve block  77  and is configured the same as stab plate  69  of FIG.  2 A and stab plate  55  of  FIG. 1A. A  stab receptacle  88  is positioned at the end of annulus conduit  87  connected to stab plate  89 . Riser connector  91  will engage the upper end of valve block  77  and conduit  56  stabs into engagement with tubing annulus conduit  87  through stab receptacle  88  at stab plate  89 . In the embodiment shown in  FIGS. 3A and 3B , passage  79  and conduit  87  define a valve block portion of the tubing annulus passage. 
   In the operation of the embodiment of  FIGS. 3A and 3B , the operator will normally close valve  82  and open valve  81  to communicate tubing annulus passage  73  with conduit  87  and the platform. Alternately, for certain operations, the operator may close valve  81  and open valve  82 . This allows communication of annulus fluid in tubing annulus conduit  87  with production passage  85  through crossover passage  83 . 
   In the embodiment of  FIGS. 4A and 4B , tubing spool  93  is shown having a tubing annulus passage  95  extending from the lower end to the upper end in the same manner as the tubing annulus passage  59  of FIG.  2 B and tubing annulus passage  73  of  FIG. 3B. A  stab receptacle  96  is positioned at the upper end of annulus passage  95  on an upper surface of tubing spool  93 . Tubing annulus passage  95 , however, could exit on the side of tubing spool  93  similar to the embodiment of  FIGS. 1A and 1B . A stab  97  at the lower end of tubing annulus passage  99  in valve block  101  will stab into tubing annulus passage  95  through stab receptacle  96 , which has a check valve at its upper end. Unlike the other embodiments, however, tubing annulus passage  99  extends completely to the upper end of valve block  101 . In the embodiment shown in  FIGS. 4A and 4B , tubing annulus passage  95  defines the tubing hanger support portion of the tubing annulus passage, and tubing annulus passage  99  defines the valve block portion of the tubing annulus passage. A stab receptacle  102  is positioned at the end of tubing annulus passage  99  connected to the upper end of valve block  101 . A stab  103  extends between passage  99  in valve block  101  and a passage  106  in riser connector  105 . Tubing annulus passage  106  leads to the exterior for coupling to conduit  56  extending alongside the riser. When valve block  101  lands on tubing spool  93 , it will make up a tubing annulus flow path between passages  106 ,  99  and  95 . A cross-over passage similar to passage  83  of  FIG. 3A  could be installed between tubing annulus passage  99  and production flow passage  100  in valve block  101 . A valve could be mounted in the cross-over passage to selectively communicate tubing annulus passage with production flow passage  100 . 
   For the first four embodiments (FIGS.  1 - 4 ), the tubing hanger support was illustrated as tubing spool  31  (FIG.  1 A),  37  (FIG.  2 B),  71  ( FIG. 3B ) or  93  (FIG.  4 B). In the embodiment of  FIGS. 5A and 5B , there is no tubing spool such as tubing spools  31 ,  57 ,  71 ,  93 . Instead, tubing hanger  107  lands in a tubular wellhead member or wellhead housing  109 . An adapter  111  is located in the bore of wellhead housing  109  for supporting tubing hanger  107 . In the embodiment shown in  FIGS. 5A and 5B , adapter  111  defines the tubing hanger support. Adapter  111  has a lower portion that lands in the bore of the upper casing hanger  113 . A locking element  112  locks adapter  111  in the bore of wellhead housing  109 . A valve block  115  lands on the upper end of wellhead housing  109 . A connector  116  connects valve block  115  to an external profile on the mandrel of wellhead housing  109 . An isolation sleeve  117  extends between the production passage in valve block  115  and the production passage in tubing hanger  107 . A tubing annulus passage  119  extends through adapter  111 , having a lower end in communication with the tubing annulus  120  and an upper end in communication with a stab receptacle  122  mounted to adapter  111 . A stab  121  extends between the upper end of tubing annulus passage  119  at the upper end of adapter  111 , communicating tubing annulus passage  119  with a tubing annulus passage  123  in valve block  115 . A check valve that is actuated by stab  121  is at the upper end of tubing annulus passage  119 . 
   Tubing annulus passage  123  of this embodiment leads to an optional annulus valve  125  on the exterior of valve block  115 . Alternately, it could lead to a dual valve as in  FIGS. 3A and 3B  or to the upper end of valve block  115  as in  FIGS. 4A and 4B . A conduit  127  on the exterior of valve block  115  leads upward to a stab plate  129  near the upper end of valve block  115 . A stab receptacle  128  is positioned at the end of annulus conduit  127  connected to stab plate  129 . A riser connector  131  connects to the upper end of valve block  115 . Conduit  56  extending alongside the riser from the platform stabs into receptacle  128  on stab plate  129  to connect with tubing annulus conduit  127 . In the embodiment shown in FIGS.  5 A and SB, tubing annulus passage  119  defines the tubing hanger support portion of the tubing annulus passage, and tubing annulus passage  123  and conduit  127  define the valve block portion of the tubing annulus passage. 
   In the operation of the embodiment of  FIGS. 5A and 5B , the step of landing a tubing spool is eliminated. After the well is drilled and cased, the operator lowers on completion riser tubing hanger  107  and adapter  111 , which land in wellhead housing  109 . After the well been perforated and tested, the operator sets a plug in the production passage of tubing hanger  107 , and then removes the completion riser. The operator then lands valve block  115  on the upper end of wellhead housing  109 . Stab  121  will establish communication between adapter passage  119  and valve block passage  123 . The communication to the surface is established through conduit  127  and conduit  56  extending downward alongside the riser. 
   Each of the embodiments described and illustrated above allow an operator to communicate with tubing hanger annulus  29 . The operator may circulate heavy fluids into tubing hanger annulus  29  when “killing” the well. It is desirous to have the capability of circulating heavy fluids without having to inject the heavy fluid through string of tubing  27  or through tubing hanger  33 . Each embodiment allows operator to circulate heavy fluids through the tubing hanger support (i.e. tubing spools  31 ,  57 ,  73 ,  93  or adapter  111 ). The operator can also monitor tubing hanger annulus pressure for maintaining and protecting the integrity of the well assembly in case there is a leak. 
   Further, it will also be apparent to those skilled in the art that modifications, changes and substitutions may be made to the invention in the foregoing disclosure. Accordingly, it is appropriate that the appended claims be construed broadly and in the manner consisting with the spirit and scope of the invention herein. For example, in the embodiment shown in  FIGS. 5A and 5B , the valve block portion of the tubing annulus passage could extend completely through valve block  115  rather than being channeled to conduit  127 .