Latching mechanism with adjustable preload

Abstract

A well pipe hanger is run and landed within a subsea wellhead assembly using a latching mechanism with an adjustable preload. The well pipe hanger has a latch ring having upward and downward facing shoulders secured to the outer diameter of the tubing hanger so that the latch ring may expand radially into a groove of the landing sub. The outer and inner diameters of the latch ring are larger at a center of the latch ring than at the upper and lower ends. The latch ring is configured to contract radially from a latched to an unlatched position in response to a predetermined overpull force. The predetermined overpull force is adjustable by adjusting the radial distance between an axial center of the latch ring and the outer diameter of the well pipe hanger.

What is claimed is: 
     
         1 . A subsea wellhead assembly comprising:
 a subsea wellhead member having a central bore defining an annular landing shoulder and an annular groove formed within an inner diameter of the bore and spaced below the landing shoulder;   a well pipe hanger having an inner and outer diameter, a central axis, and a load shoulder for landing on the landing shoulder of the well member;   a latch ring having upward and downward facing shoulders, the latch ring being carried on the outer diameter of the well pipe hanger, the latch ring being radially resilient so that the latch ring snaps radially into the groove of the wellhead member when the load shoulder lands on the landing shoulder;   wherein the latch ring is configured to contract radially from a latched to an unlatched position in response to a predetermined overpull force, allowing the load shoulder of the well pipe hanger to rise above the landing shoulder; and   the latch ring is free to snap back into the groove when the well pipe hanger is lowered back onto the landing shoulder.   
     
     
         2 . The subsea wellhead assembly of  claim 1 , wherein:
 the outer diameter of the latch ring is larger at a center of the latch ring than at the upper and lower ends;   the inner diameter of the latch ring is larger at the center of the latch ring than at the upper and lower ends; and   the latch ring defines a plurality of slots spaced equidistantly around the latch ring so that the latch ring may expand and contract radially.   
     
     
         3 . The subsea wellhead assembly of  claim 2 , wherein the predetermined overpull force is adjustable by adjusting the radial distance between an axial center of the latch ring and the outer diameter of the tubing hanger. 
     
     
         4 . The subsea wellhead assembly of  claim 2 , wherein the well pipe hanger further comprises:
 a retainer ring secured to an outer diameter of the well pipe hanger;   wherein an upper end of the latch ring is interposed in an annular space between the retainer ring and the well pipe hanger;   a well pipe hanger thread formed on a lower outer diameter surface of the well pipe hanger;   a preload ring having an inner diameter preload thread matching the well pipe hanger thread;   wherein the preload ring threads onto the well pipe hanger thread so that a lower end of the latch ring is interposed in an annular space between the preload ring and the well pipe hanger; and   tightening the preload ring decreases the amount the latch ring protrudes from the well pipe hanger and increases an axial length of the latch ring, thereby adjusting the overpull force.   
     
     
         5 . The subsea wellhead assembly of  claim 4 , wherein:
 the well pipe hanger thread has a length longer than a length of the preload thread;   the preload ring may move an axial distance along the well pipe hanger by rotating through the preload thread;   an inner diameter portion of the preload ring and the retainer ring contact an outer diameter portion of the latch ring; and   wherein moving the preload ring axially through the well pipe hanger thread and preload ring thread causes the latch ring to contract and expand radially.   
     
     
         6 . The subsea wellhead assembly of  claim 5 , wherein radial displacement of the latch ring corresponds to the predetermined axial overpull force. 
     
     
         7 . The subsea wellhead assembly of  claim 5 , wherein at least one set screw threads through the preload ring and into the tubing hanger threads to limit rotation of the preload ring. 
     
     
         8 . The subsea wellhead assembly of  claim 1 , wherein the well pipe hanger further comprises:
 a plurality of threaded bore holes formed in the outer diameter of the well pipe hanger, wherein the threaded bore holes are positioned at the same axial height and spaced so that each bore hole is equidistant from adjacent bore holes;   the latch ring defines a plurality of bores passing radially through the latch ring, each bore of the latch ring aligning with a threaded bore of the well pipe hanger;   a plurality of bolts pass through the latch ring bores to thread into the well pipe hanger bores, thereby securing the latch ring to the well pipe hanger; and   the plurality of bolts threaded into the threaded bore holes to preload the latch ring by radially displacing the latch ring.   
     
     
         9 . The subsea wellhead assembly of  claim 1 , wherein the well pipe hanger further comprises:
 a latch ring housing having an inner and outer diameter;   a well pipe hanger thread is formed on a lower outer diameter surface of the well pipe hanger;   the latch ring housing having an inner diameter thread matching the well pipe hanger thread, wherein the latch ring housing threads onto the well pipe hanger thread;   a plurality of threaded bore holes are formed in the outer diameter of the latch ring housing, wherein the threaded bore holes are positioned at the same axial height and spaced so that each bore hole is equidistant from the adjacent bore holes;   the latch ring defines a plurality of bores passing radially through the latch ring, each bore of the latch ring aligning with a threaded bore of the latch ring housing;   a plurality of bolts pass through the latch ring bores to thread into the latch ring housing bores, thereby securing the latch ring to the latch ring housing; and   wherein the plurality of bolts thread into the threaded bore holes so that the latch ring is displaced radially a predetermined amount corresponding with a predetermined axial overpull amount.   
     
     
         10 . The tubing hanger of  claim 9 , wherein rotating the latch ring housing moves the latch ring to a predetermined axial height relative to the well pipe hanger. 
     
     
         11 . A subsea wellhead assembly comprising:
 a subsea wellhead member having a central bore defining an annular landing shoulder and an annular landing groove formed within an inner diameter of the bore and spaced below the landing shoulder;   a casing hanger having an inner and outer diameter, a central axis, and a load shoulder for landing in a load shoulder of the landing sub;   a latch ring having upward and downward facing shoulders secured to the outer diameter of the casing hanger so that the latch ring may expand radially into a latched position in the groove of the subsea wellhead;   wherein the latch ring is configured to contract radially from a latched to an unlatched position in response to a predetermined overpull force;   wherein the predetermined overpull force is adjustable by adjusting a radial distance between an axial center of the latch ring and the outer diameter of the casing hanger;   wherein an outer diameter of the latch ring is larger at a center of the latch ring than at the upper and lower ends;   wherein an inner diameter of the latch ring is larger at the center of the latch ring than at the upper and lower ends; and   wherein the latch ring defines a plurality of slots spaced equidistantly around the latch ring so that the latch ring may expand and contract radially.   
     
     
         12 . The subsea wellhead assembly of  claim 11 , wherein the casing hanger further comprises:
 an annular landing protrusion formed around an outer diameter of the casing hanger, wherein the landing protrusion defines a downward facing shoulder;   a retainer ring secured to an outer diameter of the casing hanger axially beneath and abutting the downward facing shoulder of the landing protrusion;   wherein an upper end of the latch ring is interposed between the retainer ring and the casing hanger;   a preload ring mounted to the casing hanger by threads;   wherein the preload ring may move an axial distance along the casing hanger by rotating through the preload ring relative to the casing hanger;   wherein an inner diameter portion of the preload ring and the retainer ring contact outer diameter portions of the latch ring; and   wherein moving the preload ring axially causes the latch ring to contract and expand radially.   
     
     
         13 . The subsea wellhead assembly of  claim 12 , wherein:
 the larger inner and outer diameters at the center of the latch ring than at the ends of the latch ring define a latch ring protrusion that bulges outward from the latch ring; and   applying a preload force with the preload ring reduces the extent of the bulge.   
     
     
         14 . The subsea wellhead assembly of  claim 12 , wherein:
 the retainer ring further comprises an annular portion extending axially toward the preload ring, wherein an inner diameter surface of the annular portion defines a taper in contact with an outer diameter surface of the latch ring above the latch ring upward facing shoulder; and   the preload ring further comprises and annular portion extending axially toward the retainer ring, wherein an inner diameter surface of the annular portion defines a taper in contact with an outer diameter surface of the latch ring below the latch ring downward facing shoulder.   
     
     
         15 . The subsea wellhead assembly of  claim 11 , wherein:
 the casing hanger defines a plurality of threaded bore holes formed in the outer diameter of the casing hanger, wherein the threaded bore holes are positioned at the same axial height and spaced so that each bore hole is equidistant from the adjacent bore holes;   the latch ring defines a plurality of bores passing radially through the latch ring, each bore of the latch ring aligning with a threaded bore of the casing hanger;   a plurality of bolts pass through the latch ring bores to thread into the casing hanger bores, thereby securing the latch ring to the casing hanger; and   wherein the plurality of bolts threaded into the threaded bore holes such that the latch ring may displace radially to adjust a predetermined overpull amount.   
     
     
         16 . The subsea wellhead assembly of  claim 11 , wherein the casing hanger further comprises:
 a latch ring housing having an inner and outer diameter;   a casing hanger thread formed on a lower outer diameter surface of the casing hanger;   the latch ring housing having an inner diameter thread matching the casing hanger thread so that the latch ring housing threads onto the casing hanger thread, securing the latch ring housing to the casing hanger;   the latch ring housing defines a plurality of threaded bore holes formed in the outer diameter of the latch ring housing, wherein the threaded bore holes are positioned at the same axial height and spaced so that each bore hole is equidistant from the adjacent bore holes;   the latch ring defines a plurality of bores passing radially through the latch ring, each bore of the latch ring aligning with a threaded bore of the latch ring housing;   a plurality of bolts pass through the latch ring bores to thread into the latch ring housing bores, thereby securing the latch ring to the latch ring housing; and   the plurality of bolts threaded into the threaded bore holes such that the latch ring may displace radially to adjust to a predetermined overpull force.   
     
     
         17 . The subsea wellhead assembly of  claim 11 , wherein upwards pull on the casing hanger at the predetermined load will cause the latch ring to compress radially, allowing the casing hanger to be pulled from the subsea wellhead. 
     
     
         18 . A method for confirming landing of a well pipe hanger in a subsea wellhead member, the method comprising:
 (a) providing in a bore of the wellhead member a landing shoulder and an annular groove spaced below the landing shoulder;   (b) providing a well pipe hanger having a radially moveable latch ring;   (c) running the well pipe hanger into the wellhead member and landing the well pipe hanger on the landing shoulder;   (d) allowing the latch ring to contact an inner diameter wall of the bore and radially contract as the well pipe hanger enters the bore, then radially expand to latch within the groove;   (e) applying an upward axial force to the well pipe hanger, causing the latch ring to contract and release from the groove, thereby lifting the well pipe hanger from the landing shoulder; then   (e) lowering the well pipe hanger back onto the load shoulder and allowing the latch ring to radially expand back into engagement with the groove.   
     
     
         19 . The method of  claim 18 , wherein the method further comprises adjusting a preload ring prior to running of the well pipe hanger to adjust the predetermined upward axial force needed to cause a radial displacement of the latch ring.