Patent Publication Number: US-6705401-B2

Title: Ported subsea wellhead

Description:
FIELD OF THE INVENTION 
     This invention relates in general to offshore drilling and production equipment, and in particular to a subsea well system for monitoring the pressure in a non-producing string of casing through the completion system. 
     DESCRIPTION OF THE RELATED ART 
     A subsea well that is capable of producing oil or gas will have a conductor housing secured to a string of conductor pipe which extends a first depth into the well. A wellhead housing lands in the conductor housing. The wellhead housing is secured to an outer or first string of casing, which extends through the conductor 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 cased to the final depth. Each string of casing is supported at the upper end by a casing hanger. The casing hanger lands in and is supported by the wellhead. 
     In some shallow wells and in some fluid injection wells, only one string of casing is set within the outer casing. Where only one string of casing is set within the outer casing, only one casing hanger, the production casing hanger, is landed in the wellhead housing. 
     The more typical case is where multiple strings of casing are suspended within the wellhead housing to achieve the structural support for the well to the depth of the target zone. Where multiple strings of casing hangers are landed in the wellhead housing, each casing hanger is above the previous one in the wellhead housing. Between each casing hanger and the wellhead housing, a casing hanger packoff is set to isolate each annular space between strings of casing. The last string of casing extends into the well to the final depth, this being the production casing. The strings of casing between the outer casing and the production casing are intermediate casing strings. 
     When drilling and running strings of casing in the well, it is critical that the operator maintains pressure control of the well. This is accomplished by establishing a column of fluid with predetermined fluid density inside the well. During drilling operations, this fluid is circulated down into the well through the inside of the drillstring out the bottom of the drillstring and back to the surface. This column of density-controlled fluid balances the downhole pressure in the well. When setting casing, the casing is run into the pressure balanced well. A blowout preventer system is employed during drilling and running strings of casing in the well as a further safety system to insure that the operator maintains pressure control of the well. The blowout preventer system is located above the wellhead housing by running it on drilling riser to the wellhead housing. 
     When each string of casing hanger is suspended in the wellhead housing, 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. In a subsea well capable of producing oil or gas, the production fluids flow through perforations made in the production casing at the producing zone. A string of tubing extends to the producing zone within the production casing to provide a pressure controlled conduit through which the well fluids are produced. At some point above the producing zone, a packer seals the space between the production casing and the tubing to ensure that the well fluids flow through the tubing to the surface. The tubing is supported by a tubing hanger assembly that lands and locks above the production casing hanger, either in the wellhead housing, in a tubing hanger spool, or in a horizontal or spool tree, as described below. 
     Subsea wells capable of producing oil or gas can be completed with various arrangements of the production control valves in an assembly generally known as a tree. For wells completed with a conventional tree, the tubing hanger assembly lands in the wellhead housing above the production casing hanger. Alternatively, the tubing hanger assembly lands in a tubing hanger spool that is itself landed and locked to the wellhead housing. For wells completed with a horizontal or spool tree, the horizontal tree lands and seals on the wellhead housing. A tubing hanger assembly lands and seals in the horizontal tree. 
     The tubing hanger assembly in conventional trees has a flow passage for communication with the annulus surrounding the tubing. A tubing annulus bypass extends around the tubing hanger in horizontal trees. These passages allow for communication between the interior of the production casing and the interior of the tubing. Virtually all producing wells are capable of monitoring pressure in the annulus flow passage between the interior of the production casing and the exterior of the tubing. 
     A sealed annulus locates between the production casing and the next larger string of casing. Normally there should be no pressure in the annulus between the production casing and the next larger string of casing because the annular space between the production casing and the next larger string of casing is ordinarily cemented at its lower end and sealed with a packoff at the production casing hanger end. If pressure within this annulus increases, it would indicate that a leak exists in one of the strings of casing. The leak could be from several places. Regardless of where the leak is coming from, pressure build up in the annulus between the production casing and the next larger string of casing could collapse a portion of the production casing, compromising the structural and pressure integrity of the well. 
     For this reason, operators monitor the pressure in the annulus between the production casing and the next larger string of casing in land-based or above water wells. Monitoring production casing annulus pressure in a subsea well is more difficult because of lack of access to the wellhead housing below the production casing hanger packoff. Different methods have been proposed for monitoring the annulus pressure between the production casing and the next larger casing in subsea wells. However, most subsea wells do not have any ability to monitor casing annulus pressure. 
     SUMMARY OF THE INVENTION 
     In a subsea well with a tree assembly including either a tubing spool or a horizontal tree, the production casing annulus pressure and an intermediate casing annulus pressure are monitored through communication passages located in the high pressure wellhead housing. In the first embodiment, communication passages for communicating production casing annulus and intermediate casing annulus pressures extend into and up the high pressure wellhead housing, both opening on the inner surface of the high pressure wellhead housing above the lockdown hanger for the production tubing. Valves prevent the annulus pressures from communicating before the tree assembly is landed on the high pressure wellhead housing. The tree assembly has an isolation sleeve that seals to the inside of the wellhead housing below the outlets for the communication passages. After the tree assembly is landed, the valves are opened and the annulus pressures communicate through their respective passageways to the isolation sleeve, and then up to the tree assembly where the pressures are monitored. 
     In a second embodiment, communication passages for communicating the production casing annulus and the intermediate casing annulus pressures both extend from the inner surface of the high pressure wellhead housing to the exterior surface of the high pressure wellhead housing. Valves prevent the pressures from communicating before the tree assembly is landed. The tree assembly has a flying lead, which has connections that connect to both the passageway outlet for communicating the production casing annulus pressure and the passageway outlet for communicating the intermediate casing annulus pressure. The connections from the flying lead are attached to the outlets for communicating the annulus pressures. After connecting the flying lead connections from the flying lead extending down from the tree assembly, the valves are opened to allow communication of the production casing and intermediate casing annulus pressures through the passageways to the tree assembly for monitoring. 
     The third embodiment, the production casing annulus pressure is monitored. In the third embodiment, the annulus pressure communicates up the production casing housing to a passageway in the high pressure wellhead housing. The passageway extends from the inner surface of the high pressure wellhead housing to the exterior surface of the wellhead housing. In this embodiment, the wellhead has a guide base for aligning equipment as it is landed on the wellhead. High pressure wellhead housing has a guide frame attached to its outer surface that was guided to the wellhead along guide posts extending from the guide base. Mounted on the guide frame is a valve that connects to the passageway communicating the production casing annulus pressure. The valve prevents communication while the tree assembly is not attached. An extension tube extends from the valve and connects to an upward facing connection that is also mounted on the guide frame. A tree assembly has a downward facing connection, and when the tree lands on the wellhead housing, the connections are connected. When the valve is opened, the production casing annulus pressure communicates up the production casing, through the passageway in the high pressure housing, through the open valve, through the extension tube, and through the connected connections to the tree assembly for monitoring. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is an overall sectional view of an upper portion of a wellhead assembly in accordance with this invention. 
     FIG. 2 is an overall sectional view of an upper portion of wellhead assembly in accordance with a second embodiment of this invention. 
     FIG. 3 is an overall sectional view of an upper portion of wellhead assembly in accordance with a third embodiment of this invention. 
     FIG. 4 is a topdown view of a guide frame built in accordance with the third embodiment of this invention. 
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENT 
     Referring to FIG. 1, one configuration for the subsea wellhead assembly includes a low pressure wellhead housing or conductor housing  11 , which will locate at the sea floor. Low pressure wellhead housing  11  is a large tubular member that is secured to a string of conductor pipe  13 . Conductor pipe  13  extends to a first depth into the well. 
     A high pressure wellhead housing  15  lands in the low pressure wellhead housing  11 . High pressure wellhead housing  15  is a high pressure tubular member having an exterior surface  17  and an interior surface  19 . High pressure wellhead housing  15  secures to a first string of casing  21 , which extends through the conductor pipe  13  to a deeper depth into the well. Normally, the first string of casing  21  is cemented in place. 
     An intermediate casing hanger  23  and intermediate casing  25  are installed in high pressure wellhead housing  15  in the first string of casing  21 . Intermediate casing hanger  23  lands on a lower shoulder in the interior surface of high pressure wellhead housing  15 . Intermediate casing hanger  23  is sealed by an intermediate casing hanger packoff  29  to interior surface  19  of high pressure wellhead housing  15 . Intermediate casing hanger  23  secures to a string of intermediate casing  25 , which is cemented in place. 
     Production casing hanger  27  having an interior surface and an exterior surface lands on a shoulder on intermediate casing hanger  23 . Production casing hanger  27  is sealed by a production casing hanger packoff  33  to interior surface  19  of high pressure wellhead housing  15 . Production casing hanger  27  secures to production casing  31 . Production casing  31  extends through intermediate string of casing  25  to a final depth of the well. Production casing  31  is cemented in place. 
     An intermediate casing annulus  35  exists in the space surrounding intermediate casing  25 . Intermediate casing annulus  35  also surrounds intermediate casing hanger  23  up to intermediate casing hanger packoff  29 . A production casing annulus  37  exists in the space surrounding production casing  31 . Production casing annulus  37  also surrounds production casing hanger  27  up to production casing hanger packoff  33 . Normally, there would be low pressure in intermediate casing annulus  35  and production casing annulus  37 . Only a lower portion of production casing  31  is exposed to well pressure, and this exposure is through perforations (not shown). Cement in annulus  37  blocks communication upward of formation pressure from the perforations. Formation pressure may exist in production casing annulus  37  only when a leak occurs. 
     A production casing communication passageway  39  has a lower inlet in the bore  19  of high pressure wellhead housing  15 . Passageway  39  is shown schematically and would not have the curves shown in FIG. 1 in actual production. Passageway  39  begins above intermediate casing packoff  29  and below production casing packoff  33 . Passageway  39  connects with production casing valve  43 , which when closed, prevents communication with production casing annulus  37 . Preferably valve  43  is opened and closed by a remote operated vehicle (“ROV”). Passageway  39  extends upwardly after passing through valve  43 , through high pressure wellhead housing  15  and ends at a production passage outlet  45  on interior surface  19  of high pressure wellhead housing  15 . Production passage outlet  45  is located above lockdown hanger packoff  47  of lockdown hanger  49 . Lockdown hanger  49  is optional. Passageway  39  allows fluid communication between production casing annulus  37  and interior surface  19  of high pressure wellhead  15 . 
     An intermediate casing communication passageway  41  (schematically shown) extends at an upward angle into high pressure wellhead  15  from interior surface  19  from below intermediate casing packoff  29 . Intermediate passageway  41  connects with intermediate casing valve  51 , which blocks communication through passageway  41  when closed. Preferably valve  51  is ROV actuated. Intermediate passageway  41  extends upwardly after passing through intermediate valve  51 , through high pressure wellhead housing  15  and ends at an intermediate passage outlet  53  on interior surface  19  of high pressure wellhead housing  15 . Intermediate passage outlet  53  is located above lockdown hanger packoff  47  of lockdown hanger  49 . Intermediate passage  41  allows fluid communication between intermediate casing annulus  35  and interior surface  19  of high pressure wellhead  15 . 
     Communication from intermediate casing annulus  35  to intermediate passageway outlet  53  is not desired before a tree assembly  55  is installed on top of high pressure wellhead housing  15 . Therefore, intermediate valve  51  prevents the annulus pressure from communicating to intermediate passageway outlet  53 . Communication from production casing annulus  37  to production passageway outlet  45  is also not desired before a tree assembly  55  is installed on top of high pressure wellhead housing  15 . Therefore, production valve  43  prevents the annulus pressure from communicating to production passageway outlet  45 . 
     An isolation sleeve  61 , mounted to the base of tree assembly  55 , sealingly engages and attaches to interior surface of lockdown hanger  49  when tree assembly  55  is lands on the well. Tree assembly  55  has a connector  56  that secures to wellhead housing  15 . Isolation sleeve packoff  63  seals isolation sleeve  61  to the interior surface lockdown hanger  49  so that there is a seal below production passageway outlet  45 , and below intermediate passageway outlet  53 . After tree assembly  55  is installed, valves  43  and  51  can open, therefore allowing the annular pressures from production casing annulus  37  and from intermediate casing annulus  35  to communicate to outlets  45  and  53 , up the outer surface of isolation sleeve  61  to tree assembly  55 , where the pressures are monitored and communicated by a control umbilical to a gauge  64  at the surface. 
     In operation of the FIG. 1 embodiment, the well will be drilled and cased as shown in FIG.  1 . To do so, low pressure wellhead housing  11  with string of conductor pipe  13  is landed and cemented into the well to certain depth. High pressure wellhead housing  15  with first string of casing  21  from high pressure wellhead  15  is then landed and cemented into the well at a deeper depth. An intermediate hanger  23  with intermediate casing  25  extending below is landed and cemented into the well. Intermediate hanger packoff  29  sealingly connects intermediate hanger  23  to interior surface  19  of high pressure wellhead housing  15 . Intermediate casing annulus  35  surrounds intermediate casing  25  after intermediate casing  25  is cemented into place. The pressure of intermediate casing annulus  35  communicates up the outside surface of intermediate casing  25 , along the outside surface of intermediate casing hanger  23 . Intermediate hanger  23  is sealingly fixed to interior surface  19  of high pressure wellhead housing  15  so intermediate annulus  35  pressure must communicate into intermediate passageway  41 . Intermediate valve  51  prevents the pressure from communicating further until tree assembly  55  is landed. Production hanger  27  with production casing  31 , extending down to production depth, is landed and cemented into the well. Production hanger packoff  33  sealingly connects production hanger  27  to interior surface  19  of high pressure wellhead housing  15 . Production casing annulus  37  surrounds production casing  31  after production casing  31  is cemented into place. The pressure of production casing annulus  37  communicates up the outside surface of production casing  31 , along the outside surface of production casing hanger  27 . Production hanger packoff  33  sealingly fixes production hanger  27  to interior surface  19  of high pressure wellhead housing  15  so production annulus  37  pressure must communicate into production passageway  39 . Annulus valve  43  prevents the pressure from communicating further until tree assembly  55  is landed. Similarly, any pressure from casing annulus  35  communicates through passage  41  up to a closed valve  51 . 
     Lockdown hanger  49  with production tubing (not shown) is landed into the well, such that lockdown hanger packoff seals  47  sealingly engage lockdown hanger  49  to interior surface  19  of high pressure wellhead housing  15 . Tree assembly  55  lands into the well such that isolation sleeve  61  stabs into and sealingly engages to the interior surface of lockdown hanger  49 . Valves  43  and  51  are opened, preferably by a remotely operated vehicle. The pressure from intermediate casing annulus  35  communicates up through intermediate passageway  41  to intermediate passageway outlet  53  on interior surface  19  of high pressure housing  15 . Isolation sleeve packoff  63  and lockdown hanger packoff  47 , which are located below intermediate passageway outlet  53 , force the pressure from intermediate casing annulus  35  to communicate up the outer surface of isolation sleeve  61  to tree assembly  55  for monitoring. The pressure from production casing annulus  37  communicates upwardly through production passageway  39  to production passageway outlet  45  on interior surface  19  of high pressure housing  15 . Isolation sleeve packoff  63  and lockdown hanger packoff  47 , which are located below production passageway outlet  45 , force the pressure from production casing annulus  37  to communicate up the outer surface of isolation sleeve  61  to tree assembly  55  for monitoring. The outlets  45  and  53  lead to the same annular space around isolation sleeve  61 , thus commingled and are monitored by gauge  64 . 
     FIG. 2 shows a second embodiment of the well assembly. Referring to FIG. 2, a production casing annulus passageway  139  extends laterally through high pressure wellhead housing  115  from interior surface  119  towards exterior surface  117 . Production passageway  139  begins above intermediate casing hanger packoff  129  and below production hanger casing packoff  133 . Production passageway  139  connects with production casing valve  143 . Annulus valve  143  prevents pressure communication of production casing annulus  137  while closed. Production passageway  139  continues after annulus valve  143  to a production passageway outlet  145  located on exterior surface  117  of high pressure wellhead housing  115 . 
     An intermediate casing annulus passageway  141  extends laterally through high pressure wellhead housing  115  from interior surface  119  towards exterior surface  117 . Intermediate passageway  141  begins below intermediate casing hanger packoff  129 . Intermediate passageway  141  connects with intermediate casing valve  151 . Intermediate valve  151  prevents pressure communication of intermediate casing annulus  135  while closed. Intermediate passageway  141  continues after intermediate valve  151  to a intermediate passageway outlet  153  located on exterior surface  117  of high pressure wellhead housing  115 . 
     A tree assembly  155  having a flying lead  161  extending down from tree assembly, lands on high pressure wellhead housing  115 . Flying lead  161  has a flexible tubing  163  connecting with production passageway outlet  145  so that the pressure of production casing annulus  137  communicates from production passageway  139  to tree assembly  155  for monitoring, when production annulus valve  143  is open. Flying lead  161  also has an intermediate casing annulus tubing  165  connecting with intermediate passageway outlet  153 , so that the pressure from intermediate casing annulus  135  communicates from intermediate passageway  141  to tree assembly  155  for monitoring, when intermediate valve  151  is open. In this embodiment, the pressures from passageways  139  and  141  are not commingled. 
     In operation, the well will be drilled and cased in the second embodiment as shown in FIG.  2 . After tree assembly  155  lands on wellhead housing  115 , an ROV will connect flying lead tubing  163  to outlet  145  of casing annulus passageway  139 . The ROV connects flying lead tubing  165  to intermediate passageway outlet  153  on high pressure housing exterior surface  117 . Production passageway valve  143  and intermediate passageway valve  151  are both opened by the ROV. The production annulus pressure from production passageway  139  communicates through production valve  143 , through flying lead production tubing  163 , through flying lead  161  to tree assembly  155  for monitoring. The intermediate annulus pressure from intermediate passageway  141  communicates through intermediate valve  151 , through flying lead intermediate tubing  165 , through flying lead  161  to tree assembly  155  for monitoring. 
     FIGS. 3 and 4 show a third embodiment of the well assembly. Referring to FIG. 3, the guide base  271  that supports low pressure wellhead housing  211  is shown. Normally similar embodiments would also be employed in the first two embodiments. Guide base  271  has four upward extending posts  275  to help guide equipment when being landed on the well assembly. A guide frame  277  is attached to exterior surface  217  of high pressure wellhead housing  215 . Preferably prior to running wellhead housing  215 . Guide frame  277  attaches to high pressure housing  215  with a guide frame mounting ring  279 , which connects around the circumference of high pressure housing  215 . Two guide frame housing tubes  281  are attached to guide frame mounting ring  279  by guide frame extension rods  283 . Guide frame housing tubes  281  are aligned so that guide frame tubes  281  can slide down two of the guide posts  275 , therefore aligning high pressure wellhead housing  215  while landing in low pressure housing  211 . A crossbar  285  connects guide frame housing tubes  281 , which helps to provide structural stability to guide frame  277 . A short guide frame crossbar  287  connects guide frame extension rods  283  is for additional guide frame  277  stability. 
     Casing annulus valve  243  is mounted to the outer surface of guide frame mounting ring  279 . In this embodiment, valve  243  extends from mounting ring  279  to long guide frame crossbar  285  so that a remotely operated vehicle can easily reach valve  243  to open and close valve  243 . An exterior tube  289  for communicating casing annulus pressure after passing through valve  243 , extends away from valve  243  and connects to an upward facing connection  291  mounted to short guide frame crossbar  287 . 
     Referring to FIG. 3, a production casing passageway  239  extends laterally through high pressure wellhead housing  215  from interior surface  219  towards exterior surface  217 . Production passageway  239  begins above intermediate casing hanger packoff  229  and below production hanger casing packoff  233 . Production passageway  239  connects with production casing valve  243 , which is mounted to guide frame mounting ring  279 . Production valve  243  prevents pressure communication of production casing annulus  237  while closed. 
     A tree assembly  255  having a downward facing connection  293  aligns and stabs into engagement with upward facing connection  291 , while tree  255  lands on high pressure wellhead housing  215 . Downward facing connection  293  and upward facing connection  291  connect so that the pressure of production casing annulus  237  communicates from production passageway  239 , through extension tube  289  to tree assembly  255  for monitoring, when production valve  243  is open. 
     While the well assembly has been shown in three of its embodiments, it should be apparent to those skilled in the art that it is not so limited but is susceptible to various changes without departing from the scope of the invention.