Subsea Wellhead System With Hydraulically Set Seal Assemblies

Abstract

A wellhead system, the system including a wellhead housing having a central axis, an upper end, and a radially inner surface extending axially from the upper end. The system also includes a first casing string disposed within the wellhead housing. The first casing string includes a casing hanger and casing extending axially from the casing hanger. The system further includes a first ram block movably coupled to the housing and a second ram block movably coupled to the housing and radially opposed to the first ram block. Each ram block has a withdrawn position radially spaced apart from the casing hanger of the first casing string and an advanced position sealingly engaging the casing hanger of the first casing string.

What is claimed is: 
     
         1 . A wellhead system, comprising:
 a wellhead housing having a central axis, an upper end, and a radially inner surface extending axially from the upper end;   a first casing string disposed within the wellhead housing, wherein the first casing string includes a casing hanger and casing extending axially from the casing hanger;   a first ram block movably coupled to the housing;   a second ram block movably coupled to the housing and radially opposed to the first ram block;   wherein each ram block has a withdrawn position radially spaced apart from the casing hanger of the first casing string and an advanced position sealingly engaging the casing hanger of the first casing string.   
     
     
         2 . The wellhead system of  claim 1 , wherein the wellhead housing includes an annular recess extending radially outward from the inner surface of the wellhead housing, and wherein the first and second ram blocks are at least partially disposed within the annular recess. 
     
     
         3 . The wellhead system of  2 , further comprising an annular seal assembly positioned between the wellhead housing and each ram block. 
     
     
         4 . The wellhead system of  claim 1 , wherein the inner surface of the wellhead housing includes a landing shoulder, and wherein the casing hanger is seated against the landing shoulder. 
     
     
         5 . The wellhead system of  claim 4 , wherein the casing hanger has an upper end, a lower end connected to the casing, a radially inner surface extending axially from the upper end to the lower end of the casing hanger, and a radially outer surface extending axially from the upper end to the lower end of the casing hanger;
 wherein the outer surface of the casing hanger includes an annular recess configured to receive the first ram block and the second ram block.   
     
     
         6 . The wellhead system of  claim 5 , wherein the annular recess in the casing hanger is defined by a frustoconical shoulder disposed at an angle α relative to a radius of the central axis;
 wherein the first ram block sealingly engages the frustoconical shoulder in the advanced position; 
 wherein the second ram block sealingly engages the frustoconical shoulder in the advanced position. 
 
     
     
         7 . The wellhead system of  claim 6 , wherein first and second ram blocks each further include an engagement surface disposed at an angle β relative to a radius of the central axis, which is configured to engage with the frustoconical shoulder of the annular recess when the first and second ram blocks are in the advanced position. 
     
     
         8 . The wellhead system of  7  wherein the angles α and β are each between 2 and 14°. 
     
     
         9 . The wellhead system of  claim 1 , wherein the first ram block has a pair of end faces and a semi-cylindrical surface extending circumferentially between the end faces of the first ram block;
 wherein the second ram block has a pair of end faces and a semi-cylindrical surface extending circumferentially between the end faces of the second ram block;   wherein each end face of the first ram block opposes one end face of the second ram block;   wherein each end face of the first ram block is configured to engage and interlock with one of the end face of the second ram block.   
     
     
         10 . The wellhead system of  claim 1 , further comprising:
 a first actuator coupled to the wellhead housing and configured to transition the first ram block between the withdrawn and advanced positions; and   a second actuator coupled to the wellhead housing and configured to transition the second ram block between the withdrawn and advanced positions.   
     
     
         11 . The wellhead system of  claim 1 , further comprising:
 a second casing string disposed within the wellhead housing, wherein the second casing string includes a casing hanger and casing extending axially from the casing hanger; and   a third ram block movably coupled to the housing and positioned axially above the first ram block;   a fourth ram block movably coupled to the housing and positioned axially above the second ram block, wherein the fourth ram block is radially opposed to the third ram block;   wherein the third ram block has a withdrawn position radially spaced apart from the casing hanger of the second casing string and an advanced position sealingly engaging the casing hanger of the second casing string;   wherein the fourth ram block has a withdrawn position radially spaced apart from the casing hanger of the second casing string and an advanced position sealingly engaging the casing hanger of the second casing string.   
     
     
         12 . The wellhead casing of  claim 11 , wherein the casing hanger of the second casing string is seated on the casing hanger of the first casing string. 
     
     
         13 . A method of installing one or more casing string within a wellhead housing, the method comprising:
 (a) lowering a first casing string into a wellhead housing having a central axis, wherein the casing string includes a casing hanger and casing extending axially from the casing hanger;   (b) moving a first ram block coupled to the wellhead housing radially inward into sealing engagement with the casing hanger; and   (c) moving a second ram block coupled to the wellhead housing radially inward into sealing engagement with the casing hanger.   
     
     
         14 . The method of  claim 13 , further comprising:
 (d) sealing an annulus radially disposed between the wellhead housing and the casing hanger of the first casing string.   
     
     
         15 . The method of  claim 13 , wherein (b) comprises:
 (b1) moving the first ram block with a first linear actuator coupled to the wellhead housing; and   (b2) moving the second ram block with a second linear actuator coupled to the wellhead housing.   
     
     
         16 . The method of  claim 13 , further comprising:
 (e) interlocking a pair end faces of the first ram block with a pair of opposed end faces of the second ram block.   
     
     
         17 . The method of  claim 13 , further comprising:
 pumping cement down the first casing string and up an annulus between the first casing string and the wellhead housing before (b) and (c).   
     
     
         18 . The method of  claim 13 , further comprising:
 seating the casing hanger of the first casing string against an annular shoulder on an inner surface of the wellhead housing.   
     
     
         19 . The method of  claim 18 , wherein (b) and (c) comprise:
 compressing the casing hanger axially downward into the annular shoulder.   
     
     
         20 . The method of  claim 13 , further comprising:
 (d) lowering a second casing string into the first casing string and the wellhead housing, wherein the casing string includes a casing hanger and casing extending axially from the casing hanger;   (e) moving a third ram block coupled to the wellhead housing radially inward into sealing engagement with the casing hanger of the second casing string; and   (f) moving a fourth ram block coupled to the wellhead housing radially inward into sealing engagement with the casing hanger of the second casing string.   
     
     
         21 . The method of  claim 20 , further comprising:
 pumping cement down the second casing string and up an annulus between the second casing string and the first casing string before (e) and (f).   
     
     
         22 . The method of  claim 20 , further comprising:
 seating the casing hanger of the second casing string against an upper end of the casing hanger of the first casing string.   
     
     
         23 . A wellhead system, comprising:
 a wellhead housing having a central axis, an upper end, and a radially inner surface extending axially from the upper end;   a first annular recess extending radially outward from the inner surface;   a first ram block disposed in the first annular recess;   a second ram block disposed in the first annular recess axially opposite the first ram block;   a first linear actuator coupled to the wellhead housing and configured to move the first ram block radially toward and away from the second ram block;   a second linear actuator coupled to the wellhead housing and configured to move the second ram block radially toward and away from the first ram block.   
     
     
         24 . The wellhead system of  claim 23 , wherein the first annular recess is defined by an upper planar surface extending radially from the inner surface, a lower planar surface extending radially from the inner surface; and an annular surface extending axially from the upper planar surface to the lower planar surface. 
     
     
         25 . The wellhead system of  claim 24 , wherein a first annular seal assembly disposed along the upper annular surface and a second seal assembly is disposed along the lower annular surface;
 wherein each seal assembly engages the first and second ram blocks.   
     
     
         26 . The wellhead system of  claim 23 , further comprising:
 a second annular recess extending radially outward from the inner surface and axially spaced above the first annular recess;   a third ram block disposed in the second annular recess;   a fourth rain block disposed in the second annular recess axially opposite the third ram block;   a third linear actuator coupled to the wellhead housing and configured to move the third ram block radially toward and away from the fourth ram block;   a fourth linear actuator coupled to the wellhead housing and configured to move the fourth ram block radially toward and away from the third ram block.