Abstract:
A completion component such as a tubing hanger includes a lockdown mechanism with an actuating mandrel that includes a positively acting anti-backout mechanism, which can be remotely deployed. The mechanism comprises a tooth on an inwardly biased retention ring carried by the mandrel, and positively engageable with a corresponding profile on the tubing hanger. Detent pins are outwardly biased by a tubing hanger running tool latch piston to hold the tooth and profile out of engagement during installation of the tubing hanger and setting of the actuating mandrel.

Description:
BACKGROUND OF THE INVENTION 
     This invention relates to lockdown mechanisms for completion components in hydrocarbon wells. For simplicity, much of the following discussion refers to tubing hanger lockdown mechanisms, although the invention is of more general applicability. 
     Tubing hangers and other completion components have a requirement to be rigidly locked into the wellhead, horizontal christmas tree or other receptacle in which they are landed, to ensure safe operating conditions. The tubing hanger is typically provided with an integral lock mechanism which when activated secures the tubing hanger to the wellhead. Any subsequent pressure load below the hanger will then not cause the hanger to rise within the wellbore, which would result in unsafe operating conditions. 
     Many tubing hanger lock mechanisms utilize an activating mandrel with a 4 degree taper to take account of equipment stack up tolerances. Activating mandrels with 4 degree tapers (or larger) are prone to work loose under certain operating conditions (e.g., vibration, cyclic loading, slug flow, etc.). This can lead to a reduction of the lock mechanism retention capacity, causing an unsafe condition. 
     Existing methods of retaining the mandrel in the set condition rely on either manual intervention with additional back up equipment (e.g., lockdown bolts in surface equipment), or integral devices that rely on friction contact with the activating mandrel. 
     SUMMARY OF THE INVENTION 
     The present invention provides a completion component having a lockdown mechanism comprising: 
     an actuating mandrel provided with a taper surface; 
     a locking dog engageable with the taper surface for movement between contracted and expanded positions; 
     a locking member carried by the actuating mandrel or completion component and having a radially directed locking profile; 
     a radially directed complementary locking profile being provided on the completion component or actuating mandrel, the locking profile being radially biased into engagement with the complementary locking profile so as to restrain the actuating mandrel against axial movement relative to the completion component; and 
     a running tool latch mechanism engageable with the locking member during installation of the completion component so as to move the locking profile and complementary locking profile out of engagement against said bias, whereby the actuating mandrel is free to move axially of the completion component. 
     Thus the invention provides a completion component lockdown mechanism with an actuating mandrel that includes a positively acting anti-backout device, which can be remotely deployed. 
     Preferably the locking profile and complementary locking profile comprise teeth having a positive rake angle such that forces acting on the actuating mandrel in a direction tending to move the locking dog towards the contracted position also cause the locking profile and complementary locking profile to move into tighter engagement. 
     The locking profile and/or the complementary locking profile may comprise an axially spaced series of teeth, to accommodate completion component stackup tolerances. 
     The lockdown mechanism may comprise a pin having a first end engageable by a latch piston of the running tool latch mechanism, and a second end arranged to move the locking member against said radial bias when the first end is so engaged. The pin first end may comprise a ball bearing. 
     The locking member may be a split ring which, for example, is radially inwardly biased and is carried in a groove formed in an axial bore of the actuating mandrel. 
     Further preferred features of the invention are in the following description of an illustrative embodiment. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 shows a tubing hanger with a lockdown mechanism embodying the invention, the tubing hanger being latched onto a running tool (“THRT”) and the lockdown mechanism being shown in an inactive (contracted) condition; 
     FIG. 2 shows a portion of FIG. 1 on an enlarged scale; 
     FIGS. 2 a  and  2   b  show portions of FIG. 2 on an enlarged scale; 
     FIG. 3 shows the tubing hanger and THRT of FIG. 1 but with the lockdown mechanism activated (expanded); 
     FIG. 3 a  is an enlargement of a portion of FIG. 3; and 
     FIGS. 4 and 4 a  correspond to FIGS. 3 and 3 a , but show the THRT latch disengaged from the tubing hanger and the anti-backout device positively engaging the lockdown mechanism. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The preferred embodiment of the invention comprises a THRT  10  and a tubing hanger  12  having a lockdown mechanism that incorporates a positive anti-backout device. This device has three primary components: 1) a retention ring incorporating a locking profile, 2) a detent pin, and 3) a complementary locking profile on the tubing hanger. 
     1) Retention Ring 
     As shown, the retention ring  14  is an inwardly biased split ring with a single inner circumferential tooth  16  (FIG. 2 a ). The tooth  16  is undercut to provide a locking profile with a positive rake angle R. The retention ring  14  is housed within an internal recess profile  28  on a lockdown mechanism actuating mandrel  26 . A collar  30  threaded into the top of the actuating mandrel  26  keeps the retention ring  14  within the recess profile  28 . 
     2) Detent Pins 
     Upper  18  and lower  20  detent pins are distributed around the circumference of the tubing hanger  12 . Each detent pin  18 ,  20  is securely retained within a hole extending radially through the tubing hanger upper body and comprises a ball bearing  22 ,  24  at its radially inner end. The length of each pin inclusive of the ball bearing is slightly greater than the thickness of the tubing hanger upper body in which it is housed, for reasons further explained below. 
     3) Complementary Locking Profile 
     This profile  32  comprises series of axially spaced, circumferential tooth grooves  34  on the outer surface of the tubing hanger upper body, between the upper  18  and lower  20  detent pins. It is made of sufficient axial length to accommodate the vertical tolerance stack of the actuating mandrel  26 . Each groove  34  provides a mating profile for the retention ring tooth  16  and thus likewise is undercut to produce a positive rake angle R. 
     Operating Principle 
     First, the tubing hanger lockdown mechanism is retracted ready for installation of the hanger in the wellhead. For this purpose, the actuating mandrel  26  is raised, substantially withdrawing its taper surface  36  from behind a lock ring  38 , as shown in FIG.  1 . 
     Then the THRT  10  is made up to the tubing hanger  12 . During this process the THRT latch piston  40  is extended. The lower end of the piston  40  moves a latch ring  42  into a corresponding internal profile in the tubing hanger  12  upper body, to latch the tubing hanger  12  onto the running tool  10 . The body of the latch piston  40  moves behind enlarged tips  44  of collet fingers  46 , retaining them beneath a shoulder inside the actuating mandrel collar  30 . In this way, the collar  30  is trapped between the finger tips  44  and the lower end of a tubing hanger setting piston assembly  48 , from which the collet fingers  46  extend. The tubing hanger setting piston assembly is vertically movable with respect to the latch ring  42 . The lockdown mechanism actuating mandrel is thereby rigidly connected for movement with the setting piston assembly  48 , relative to the tubing hanger upper body. 
     The vertical movement of the latch piston  40  past the ball bearings  22 ,  24  causes outward radial displacement of the detent pins  18 ,  20 , causing their rounded outer ends to sit proud of the tubing hanger upper body outside diameter. 
     The tubing hanger  12  and attached tubing (not shown) is then picked up, run in hole, landed and locked into the wellhead. During the process the THRT setting piston assembly  48  is extended. The vertical travel of the THRT setting piston assembly  48  moves the actuating mandrel  26  down, expanding the tubing hanger lock ring  38  into the wellhead profile  50  (FIG. 3 a ), securing the hanger. As the actuating mandrel  26  moves down, the protruding ends of the detent pins  22 ,  24  ride up a ramp surface  52  on the retention ring  14 , causing it to expand into the retention groove profile  28 . In this expanded condition, a radial clearance exists between the tooth  16  and the complementary locking profile  32 . On completion of the setting sequence but prior to disconnection of the THRT from the tubing hanger (see FIGS. 3 and 3 a ), the retention ring tooth  16  will be opposite (or very close to), a retention groove  34  on the tubing hanger upper body, but will be held clear of the complementary locking profile  32 . 
     The THRT is next disengaged from the tubing hanger and retrieved to the surface. In the process the THRT latch piston  40  is retracted. The vertical movement of the piston  40  frees the pins  18 ,  20  for inward movement and allows the retention ring  14  to contract to its free state. The retraction of the retention ring  14  will engage the positive rake tooth  16  into one of the grooves  34  of the complementary locking profile  32 . The actuating mandrel  26  is now positively retained on the tubing hanger  12  upper body (FIGS. 4 and 4 a ). Withdrawal of the latch piston  40  disengages the latch ring  42  from the tubing hanger  12  and allows the collet fingers to flex inwardly for disengagement from the collar  30 . 
     Various modifications will be readily apparent. For example, the locking tooth  16  may be provided on the tubing hanger upper body, with the complementary locking profile on the retention ring  14 . Additionally or alternatively, more than one locking tooth  16  may be provided. The retention ring  14  may be outwardly biased and housed in the tubing hanger upper body, with the complementary locking profile on the actuating mandrel  26 . In that case the retention ring is held contracted out of engagement with the complementary locking profile, for example by bolts or bosses extending through the wall of the tubing hanger upper body and having heads engageable in vertically extending undercut camming grooves formed on the outside of the latch piston  40 . 
     It should be recognized that, while the present invention has been described in relation to the preferred embodiments thereof, those skilled in the art may develop a wide variation of structural and operational details without departing from the principles of the invention. Therefore, the appended claims are to be construed to cover all equivalents falling within the true scope and spirit of the invention.