Workover Riser Compensator System

Abstract

A tensioning apparatus for applying a substantially constant tension to a workover riser ( 12 ) includes a first portion ( 40 ) adapted to be coupled to a workover riser, a second portion ( 44 ) adapted to be coupled to a marine riser ( 14 ) and tensioning means ( 46 ) for providing relative movement between the first portion and the second portion to, in use, tension the workover riser.

1 . A tensioning apparatus for applying a substantially constant tension to a workover riser, the tensioning apparatus including:
 a first portion adapted to be coupled to a workover riser;   a second portion adapted to be coupled to a marine riser; and   tensioning means for providing relative movement between the first portion and the second portion to, in use, tension the workover riser.   
   
   
       2 . The tensioning apparatus of  claim 1 , wherein the tensioning apparatus further includes an apparatus body, the apparatus first portion being integral with the apparatus body. 
   
   
       3 . The tensioning apparatus of  claim 2 , wherein the tensioning apparatus body defines a body throughbore. 
   
   
       4 . The tensioning apparatus of  claim 3 , wherein when the apparatus body is connected to a workover riser, the body throughbore is in fluid communication with the workover riser. 
   
   
       5 . The tensioning apparatus of  claim 2 , wherein in use, a lower end of the apparatus body is adapted to be coupled to a lower section of a workover riser. 
   
   
       6 . The tensioning apparatus of  claim 2 , wherein, also in use, an upper end of the apparatus body is adapted to be coupled to an upper section of a workover riser. 
   
   
       7 . The tensioning apparatus of  claim 6 , wherein the workover riser upper section includes an apparatus for providing variation in length of the workover riser. 
   
   
       8 . The tensioning apparatus of  claim 1 , wherein the second portion is adapted to engage a no-go defined by the marine riser. 
   
   
       9 . The tensioning apparatus of  claim 8 , wherein the no-go is a shoulder. 
   
   
       10 . The tensioning apparatus of  claim 9 , wherein the second portion is moveable, in use, between a run-in configuration in which the second portion will not engage the shoulder and an activated configuration in which the second portion engages the marine riser shoulder. 
   
   
       11 . The tensioning apparatus of  claim 10 , wherein the second portion is radially moveable between the run-in configuration and the activated configuration. 
   
   
       12 . The tensioning apparatus of  claim 11 , wherein the second portion is radially movable by radial expansion. 
   
   
       13 . The tensioning apparatus of  claim 12 , wherein once radially expanded, the second portion engages the marine riser shoulder by landing on the shoulder. 
   
   
       14 . The tensioning apparatus of either of  claim 12 , wherein the second portion comprises at least one radially moveable element. 
   
   
       15 . The tensioning apparatus of  claim 14 , wherein the second portion comprises a plurality of radially movable elements. 
   
   
       16 . The tensioning apparatus of  claim 15 , wherein the radially moveable elements in the run-in configuration define an annular collar. 
   
   
       17 . The tensioning apparatus of  claim 16 , wherein the annular collar is mounted around the apparatus body. 
   
   
       18 . The tensioning apparatus of  claim 14 , wherein in the activated configuration, the at least one radially moveable element is displaced radially away from the apparatus body. 
   
   
       19 . The tensioning apparatus of  claim 14 , wherein the tensioning means includes an expansion surface adapted to expand the at least one radially moveable element to the activated configuration. 
   
   
       20 . The tensioning apparatus of  claim 19 , wherein the expansion surface engages a complementary surface defined by the at least one radially moveable element. 
   
   
       21 . The tensioning apparatus of  claim 19 , wherein the expansion surface is adapted to move axially with respect to the apparatus body. 
   
   
       22 . The tensioning apparatus of  claim 21 , wherein the expansion surface is adapted to be moved axially with respect to the apparatus body by hydraulic pressure. 
   
   
       23 . The tensioning apparatus of  claim 1 , wherein the second portion is releasably axially fixed with respect to the first portion. 
   
   
       24 . The tensioning apparatus of  claim 2 , wherein the second portion is releasably fixed to the apparatus body. 
   
   
       25 . The tensioning apparatus of  claim 24 , wherein the second portion is releasably fixed to the apparatus body by shear screws. 
   
   
       26 . The tensioning apparatus of  claim 24 , wherein the second portion is releasably fixed by any suitable restraining means. 
   
   
       27 - 48 . (canceled) 
   
   
       49 . A latch for separating a workover riser from a sub sea isolation system in the event of over-tensioning of the workover riser the latch including:
 a first portion adapted to be connected to a sub sea isolation system;   a second portion adapted to be connected to a workover riser, the second portion being moveable relative to the first portion;   latching means releasably connecting the first portion to the sub sea isolation system;   wherein, in use, when the tension in the workover riser exceeds a pre-determined value, relative movement of the second portion with respect to the first portion releases the latching means from the sub sea isolation system such that the workover riser is separated from the sub sea isolation system.   
   
   
       50 . The latch of  claim 49 , wherein the second portion moves relative to the first portion at a pre-determined tension which is selected, in use, to ensure that riser tensioning device will raise the workover riser clear of the BOP rams, permitting unobstructed closure of the rams. 
   
   
       51 . The latch of  claim 49 , wherein the latch is adapted to receive a sub sea isolation system control means. 
   
   
       52 . The latch of  claim 51 , wherein the sub sea isolation system control means is a control line. 
   
   
       53 . The latch of  claim 52 , wherein the latch includes a control passage adapted to provide communication between the control line and the sub sea isolation system. 
   
   
       54 . The latch of  claim 53 , wherein a first section of the control passage is defined by the first latch portion, and a second section of the control passage is defined by the second latch portion. 
   
   
       55 . The latch of  claim 53 , wherein when the second latch portion moves relative to the first latch portion, the control passage is broken, causing, in use, the sub sea isolation system to close. 
   
   
       56 . The latch of  claim 53 , wherein the control passage is a hydraulic line. 
   
   
       57 . The latch of  claim 53 , wherein the control passage is a hydraulic conduit providing, in use, fluid communication between the sub sea isolation system hydraulic control line and the sub sea isolation system. 
   
   
       58 . The latch of  claim 49 , wherein in use, when the workover riser separates from the sub sea isolation system, a workover riser retainer valve closes. 
   
   
       59 . The latch of  claim 49 , wherein the latch further includes compensation means for compensating for the pressure end load force applied to the workover riser by well pressure. 
   
   
       60 . The latch of  claim 59 , wherein the compensation means includes a piston and a piston chamber, the piston being adapted to reciprocate within the piston chamber. 
   
   
       61 . The latch of  claim 60 , wherein the piston chamber is adapted to receive a fluid. 
   
   
       62 . The latch of  claim 61 , wherein the piston chamber is adapted to receive fluid, in use, from the workover riser. 
   
   
       63 . The latch of either of  claim 61 , wherein the piston chamber is adapted to receive a fluid at well pressure. 
   
   
       64 . The latch of  claim 61 , wherein in use, the introduction of fluid into the piston chamber results in an increase in pressure in the piston chamber. 
   
   
       65 . The latch of  claim 64 , wherein an increase in piston chamber pressure acts on the piston. 
   
   
       66 . The latch of  claim 65 , wherein the pressure applied to the piston is, in turn, applied by the piston, in use, to the workover riser as a counter force, the counter force opposing the end load force. 
   
   
       67 . The latch of  claim 66 , wherein the counter force applied, in use, by the piston to the workover riser is proportional to the end load force. 
   
   
       68 . The latch of  claim 60 , wherein the area of the compensation piston is between 75-95% of the area of the latch. 
   
   
       69 . A compensator system for applying a substantially constant tension to a workover riser and permitting variation in the overall length of the workover riser, the system including:
 a lower body having a first portion adapted to be coupled to a lower section of a workover riser, and a second portion adapted to be coupled to a marine riser,   tensioning means for providing relative movement between the first portion and the second portion to tension the lower workover riser section; and   an upper body adapted to be connected to an upper section of the workover riser, the upper body being adapted to move relative to the lower body to permit variation in the overall length of the workover riser.   
   
   
       70 - 71 . (canceled) 
   
   
       72 . A riser assembly including:
 a marine riser;   a workover riser;   a compensator system including:   a lower body having a first portion adapted to be coupled to a lower section of the workover riser, and a second portion adapted to be coupled to the marine riser,   tensioning means for providing relative movement between the first portion and the second portion to tension the lower workover riser section; and   an upper body adapted to be connected to an upper section of the workover riser, the upper body being adapted to move relative to the lower body to permit variation in the overall length of the workover riser; and   a latch for separating the workover riser from a sub sea isolation system in the event of over-tensioning of the workover riser.   
   
   
       73 - 76 . (canceled)