Abstract:
A latching assembly includes a first mating portion and a second mating portion disposed adjacent and rotationally restrained relative to the first mating portion. A first cam member having a first cam profile is mounted on the first mating portion. A second cam member having a second cam profile is mounted on the second mating portion. The second cam profile is adapted to inter-fit with the first cam profile. Torque induced by the cam members when the cam profiles are engaging rotates the first cam member until the first cam profile is inter-fitted with the second cam profile.

Description:
BACKGROUND OF THE INVENTION 
     1. Technical Field 
     The invention relates generally to offshore systems employed for conducting petroleum-related operations, such as drilling and testing productivity of a well, producing fluids from a reservoir, and so forth. More specifically, the invention relates to an apparatus for connecting retrievable subsea components of the offshore system. 
     2. Background Art 
     Offshore systems that are adapted for conducting petroleum-related operations in relatively deep water generally comprise a floating vessel, a marine riser, a subsea wellhead, and a subsea blowout preventer stack. The wellhead is positioned below the floating vessel and secured to the seafloor. The blowout preventer stack is mounted on the wellhead and connected to the floating vessel by the marine riser. The marine riser provides a conduit through which tools and fluid can be communicated between the floating vessel and one or more wells beneath the wellhead. Typically, a dynamic positioning system which comprises active means of monitoring position combined with thruster control is used to keep the floating vessel on station. However, a dynamically positioned vessel is subject to drive-off, i.e., rapid evacuation from the operation site, at all times. A drive-off situation may be caused by a number of reasons, some of which include problems with the active means of monitoring position, failure of thrusters, power shutdown on the vessel, storm, and ocean current anomalies. 
     In a drive-off situation, the marine riser must be disconnected from the blowout preventer stack to permit the vessel to evacuate the operation site. However, before disconnecting the marine riser, the well must be controlled and prepared for abandonment. In some offshore systems, subsea intervention trees, also called subsea internal trees, provide the vessel with the ability to control and quickly disconnect from the well. The subsea intervention tree is usually secured in the blowout preventer stack and includes a valve assembly and a latch assembly. The valve assembly includes one or more valves which may be operated to control and seal the well. The latch assembly includes a lower mating portion and an upper mating portion. The lower mating portion is attached to the valve assembly and the upper mating portion is coupled to a landing string. When the mating portions are connected, the subsea intervention tree can be lowered into the blowout preventer stack on the landing string. The upper mating portion can be released from the lower mating portion to allow the landing string to be retrieved from the blowout preventer stack and pulled to a height which will permit the vessel to leave the operation site safely. 
     After the emergency event, the vessel may return to the operation site and again re-connect to the well. The landing string with the upper mating portion can be lowered into the blowout preventer stack to allow the upper mating portion to re-connect to the lower mating portion. The upper mating portion typically includes hydraulic connectors which are arranged in a certain order and which must be properly connected to similarly arranged hydraulic connectors on the lower mating portion. To allow proper connection of the connectors, alignment devices are generally provided on the mating portions. These alignment devices will not allow the upper mating portion to contact the lower mating portion until the upper mating portion achieves a certain positional alignment with respect to the lower mating portion. The landing string is usually rotated to place the upper mating position in the desired positional alignment with respect to the lower mating portion. However, in deep water, the weight and length of the landing string make it difficult to properly align the mating portions by rotating the landing string. Therefore, it is desirable to have a latch mechanism with mating portions that can re-connect without the need to manipulate the landing string to achieve a certain positional alignment between the mating portions. 
     SUMMARY OF THE INVENTION 
     In general, in one aspect, a latching assembly comprises a first mating portion and a second mating portion disposed adjacent and rotationally restrained relative to the first mating portion. A first cam member having a first cam profile is mounted on the first mating portion, and a second cam member having a second cam profile is mounted on the second mating portion. The second cam profile is adapted to inter-fit with the first cam profile. Torque induced by the cam members when the cam profiles are engaging rotates the first cam member until the first cam profile is inter-fitted with the second cam profile. 
     Other aspects and advantages of the invention will be apparent from the following description and the appended claims. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 illustrates an offshore system with a subsea intervention tree secured in a blowout preventer stack. 
     FIG. 2A is an elevation view of the upper subassembly of the subsea intervention tree shown in FIG.  1 . 
     FIG. 2B is a cross section of the upper subassembly shown in FIG. 2A along line A—A, with the left half showing a locked position and the right half showing a released position. 
     FIG. 3A is an elevation view of the lower subassembly of the subsea intervention tree shown in FIG.  1 . 
     FIG. 3B is a partial cross section of the lower subassembly shown in FIG. 3A along line B—B. 
     FIG. 3C is a cross section of the lower subassembly shown in FIG. 3B along line C—C. 
    
    
     DETAILED DESCRIPTION 
     Referring to the drawings wherein like characters are used for like parts throughout the several views, FIG. 1 depicts a well  10  which traverses a fluid reservoir  12  and an offshore system  14  suitable for testing productivity of the well  10 . The offshore system  14  comprises a surface system  16 , which includes a production vessel  18 , and a subsea system  20 , which includes a blowout preventer stack  22  and a subsea wellhead  24 . The subsea wellhead  24  is fixed to the seafloor  26 , and the blowout preventer stack  22  is mounted on the subsea wellhead  24 . The blowout preventer stack  22  includes ram preventers  28  and annular preventers  30  which may be operated to seal and contain pressure in the well  10 . A marine riser  32  connects the blowout preventer stack  22  to the vessel  18  and provides a passage  34  through which tools and fluid can be communicated between the vessel  18  and the well  10 . 
     The subsea system  20  further comprises a subsea intervention tree  36  which is positioned in the blowout preventer stack  22 . The subsea intervention tree  36  includes an upper subassembly  38  and a lower subassembly  40 . The upper subassembly  38  is coupled to a connector assembly  42  by a mandrel  44 , and the connector assembly  42  is in turn coupled to an upper pipe string or landing string  46  which extends upwardly to the vessel  18 . The lower subassembly  40  is coupled to a lower pipe string  48  which is suspended in the well  10  by a fluted hanger  50 . The subsea intervention tree  36  and the mandrel  44  have bores (not shown) which allow fluid communication between the upper pipe string  46  and the lower pipe string  48 . Fluid may flow from the reservoir  12 , through the pipe strings  46  and  48 , to the vessel  18 . The lower pipe string  48  is equipped with a test device  52  which is responsive to fluid properties and/or other reservoir parameters. 
     The lower subassembly  40  includes one or more valves (not shown) which may be actuated to permit or prevent fluid communication between the pipe strings  46  and  48 . In the event that the valves in the lower subassembly  40  fails, the ram preventers  28  in the blowout preventer stack  22  may be operated to shear the mandrel  44  and seal the well  10 . The upper subassembly  38  is releasably connected to the lower subassembly  40  by a latch mechanism which includes an upper cam  53  (shown in FIG. 2A) and a lower cam  55  (shown in FIG.  3 A). When the upper subassembly  38  is connected to the lower subassembly  40  as shown, control lines  54  from the vessel  18  are routed through the connector assembly  42  and upper subassembly  38  to the lower subassembly  40 . The control lines  54  provide the fluid pressure necessary to operate the valves in the lower subassembly  40 . 
     Referring to FIGS. 2A and 2B, the upper subassembly  38  includes a housing body  56 . The upper cam  53  is secured to the outer surface  60  of the housing body  56  by fasteners, e.g., bolts  62 . The upper cam  53  has a cam profile which includes a helical profile  64  that terminates in a slot  66 . The housing body  56  is provided with a bore  68 . A piston cap  70  is disposed in the bore  68  and secured to the housing body  56  by a split ring  72 . As shown, one end of the split ring  72  is secured to the housing body  56  by fasteners, e.g., screws  74 , and another end of the split ring  72  is disposed in a recess  75  on the piston cap  70 . The split ring  72  is secured to the piston cap  70  by shear pins  76  and may spin freely in the recess  75  when the shear pins  76  are sheared. 
     The piston cap  70  has a bore  80  for receiving a lower portion  82  of the mandrel  44  (shown in FIG.  1 ). The lower mandrel portion  82  is secured to the piston cap  70  by a threaded connection  84  or by other suitable means. The housing body  56 , the piston cap  70 , and the lower mandrel portion  82  define a space  86  for receiving a piston  88 . Seals  90  are provided between the piston  88  and the housing body  56 , the piston cap  70 , and the lower mandrel portion  82  such that sealed chambers  92  and  94  are defined within the space  86 . The piston  88  is arranged to reciprocate within the space  86  in response to differences in fluid pressures in the sealed chambers  92  and  94 . As illustrated in the right half of the drawing of FIG. 2B, the piston cap  70  limits the upward movement of the piston  88 . As illustrated in the left half of the drawing of FIG. 2B, a shoulder  96  on the lower mandrel portion  82  limits the downward movement of the piston  88 . 
     A lock ring  100  is secured to the lower mandrel portion  82 . When the piston  88  rests on the shoulder  96 , as illustrated in the left half of the drawing of FIG. 2B, the lower end of the piston  88  is received in a recess  99  between the lock ring  100  and the lower mandrel portion  82 . A seal sub  102  is secured to the lower end of the lower mandrel portion  82 . The seal sub  102  has a bore  105  that is co-extensive with a bore  106  of the lower mandrel portion  82 . The bore  106  is in fluid communication with the upper pipe string  46  (shown in FIG.  1 ). Slots  107  (shown in FIG. 2A) are provided along a circumference of the lower mandrel portion  82 . Hydraulic lines (not shown) run from the upper end  109  of the housing body  56  to the lower end  111 . The hydraulic lines are adapted to be connected to the control lines  54  (shown in FIG.  1 ). 
     Referring to FIGS. 3A-3C, the lower subassembly  40  includes a housing body  108 . The lower cam  55  is integrated with the outer surface  110  of the housing body  108 . In the illustrated embodiment, the lower cam  55  has a cam profile which includes a helical profile  112  that terminates in a key  114 . The helical profile  112  and the key  114  are adapted to inter-fit with the helical profile  64  and the slot  66 , respectively, of the upper cam  53  (shown in FIGS.  2 A and  2 B). In an alternate embodiment, multiple keys, similar to key  114 , may be distributed along the helical profile  112 , and multiple slots, similar to slot  66 , may be provided on the helical profile  64  to receive the keys. 
     The key  114  is provided with a helical shoulder  115 . When the helical profile  64  contacts the helical shoulder  115  or helical profile  112 , induced torque by the upper cam  53  and the lower cam  55  rotates the upper cam  53  and the housing body  56  (shown in FIGS. 2A and 2B) about the lower mandrel portion  82  until the slot  66  engages the key  114 . Friction between the helical profiles  64  and  112  as the upper cam  53  rotates relative to the lower cam  55  can be kept to a minimum by coating the helical profiles  64  and  112  with Teflon or other material that has a low coefficient of friction. Alternately, a ball bearing may be provided between the helical profiles. Hydraulic lines  116  (shown in FIG. 3C) are provided in the housing body  108 . When the upper cam  53  and the lower cam  55  are inter-fitted, the hydraulic lines  116  are connected to the hydraulic lines in the housing body  56  (shown in FIG. 2A) via hydraulic connectors  117  on the upper end  118  of the housing body  108 . 
     The housing body  108  includes a lock ring profile  120  (shown in FIG. 3B) which is adapted to engage the lock ring  100  on the lower mandrel portion  82  and a seal bore  122  which is adapted to receive the seal sub  102  on the lower mandrel portion  82 . The housing body  108  also include torsional keys  124  which are adapted to interlock with the slots  107  on the lower mandrel portion  82 , thereby securing the upper subassembly  38  to the lower subassembly  40 . A flapper valve  126  is arranged in the housing body  108 , between the seal bore  122  and a lower bore  128  in the housing body  108 . The flapper valve  126  may be operated to allow or prevent fluid communication between the bores  122  and  128 . The bore  128  is in fluid communication with the lower pipe string  48  (shown in FIG.  1 ). 
     In operation, the subsea intervention tree  36  is landed in the blowout preventer stack  22  as shown in FIG.  1 . The flapper valve  126  is normally open to allow fluid to flow from the reservoir  12 , through the lower pipe string  48  and the upper pipe string  46 , to the vessel  18 . In the event of an emergency situation, the flapper valve  126  may be closed to prevent fluid communication between the lower pipe string  48  and the upper pipe string  46 . If the emergency situation calls for abandonment of the well, the upper subassembly  38  is released from the lower subassembly  40  and the upper pipe string  46  is pulled to the vessel  18 . The marine riser  32  is then released from the blowout preventer stack  22  and pulled to a height which will allow the vessel  18  to move away from the well site. 
     After the emergency situation, the vessel  18  can return to the well site and the marine riser  32  can be re-connected to the blowout preventer stack  22 . Once the marine riser  32  is connected to the blowout preventer stack  22 , the upper subassembly  38  may be lowered to the lower subassembly  40  on the upper pipe string  48 . As the upper subassembly  38  is lowered toward the lower subassembly  40 , the shear pins  76  prevent the housing body  56  from rotating about the lower mandrel portion  82 . If the housing body  56  rotates about the lower mandrel portion  82  as the upper subassembly  38  is lowered toward the lower subassembly  40 , the control lines  54  will wrap around the mandrel  44  and may break. The upper subassembly  38  is lowered until the helical profile  64  on the upper cam  53  contacts the helical shoulder  115  or helical profile  112  on the lower cam  55 . When the helical profile  64  contacts the helical shoulder  115  or helical profile  112 , the upper cam  53  tends to rotate relative to the lower cam  55 . However, the upper cam  53  will not rotate relative to the lower cam  55  until the torque induced by the cams is sufficient to shear the shear pins  76 . 
     Of course, there are other means of preventing the housing body  56  from rotating about the lower mandrel portion  82  as the upper subassembly  38  is lowered toward the lower subassembly  40 . A collet or just friction may be used in place of the shear pins  76  to prevent the housing body  56  from rotating until a minimum torque is achieved. When the shear pins  76  are sheared, the housing body  56  rotates freely about the lower mandrel portion  82  and the upper cam  53  rotates freely relative to the lower cam  55 . As the upper cam  53  rotates, the helical profile  64  rides on the helical shoulder  115  until the key  114  is received in the slot  66 . The hydraulic lines in the housing bodies  56  and  108  are automatically aligned and connected when the key  114  is received in the slot  66 . 
     The upper subassembly  38  is secured to the lower subassembly  40  by rotating the mandrel  44  until the slots  107  on the lower mandrel portion  82  interlock with the torsional keys  124  in the housing body  108 . When the torsional keys  124  engage the slots  107 , fluid pressure differential may be created between the sealed chambers  92  and  94  to move the piston  88  downwardly. When the piston  88  rests on the shoulder  96  of the lower mandrel portion  82 , the lower end of the piston  88  is forced into the recess  99  between the mandrel portion  82  and the lock ring  100  and the lock ring  100  is radially expanded to engage the lock ring profile  120 . To unlatch the upper subassembly  38  from the lower subassembly  40 , fluid pressure differential is created between the sealed chambers  92  and  94  to move the piston  88  upwardly. When the piston  88  moves upwardly, the lock ring  100  is released from the lock ring profile  120 . The mandrel  44  is then lifted to release the torsional keys  124  from the slots  107 , allowing the upper subassembly  38  to be lifted from the lower subassembly  40 . 
     The invention provides advantages. First, torque induced by the upper cam  53  and the lower cam  55  when the cam profiles are engaging rotates the upper subassembly  38  relative to the upper pipe string or landing string  46 . As the upper cam  53  rotates, the slot  66  on the upper cam  55  and the key  114  on the lower cam  55  self-align without manipulating the landing string  46  to place the upper subassembly  38  in a certain positional alignment with respect to the lower subassembly  40 . Second, when the key  114  is received in the slot  66 , the hydraulic lines in the subassemblies  38  and  40  are automatically aligned and connected. Finally, the upper cam  53  and the lower cam  55  can be used with any subassemblies that need to be releasably connected together and where proper alignment of the subassemblies is critical. 
     While the invention has been described with respect to a limited number of embodiments, those skilled in the art will appreciate numerous variations therefrom without departing from the spirit and scope of the invention. For example, the upper cam  53  and the lower cam  55  can be interchanged such that the helical profile  64  with the slot  66  is provided on the lower subassembly  40  and the helical profile  112  with the key  114  is provided on the upper subassembly  38 . A removable sleeve may be provided on the upper cam  53  to guide the upper cam  53  to the lower cam  55 . The upper cam  53  and the housing body  56  can be coupled to the piston cap  70  or the lower mandrel portion  82  in any suitable manner as long as the upper cam  53  and the housing body  56  is free to rotate relative to the lower cam  55 . One suitable manner may be providing bearings between the piston cap  70  and the housing body  56  so that the housing body  56  is free to rotate about the lower mandrel portion  82 .