Casing float tool

Abstract

A rupture disc assembly and a float tool incorporating the rupture disc assembly is disclosed. The rupture disc assembly may include a rupture disc assembly comprising a rupture disc, an upper tubular portion and a lower tubular portion, and a securing mechanism for holding the rupture disc between the upper and lower tubular portions. A float tool for creating a buoyant chamber in a casing string may include the rupture disc assembly and a sealing device for sealing the lower end of the casing string, the buoyant, sealed chamber may be created there between. In operation, applied fluid pressure causes the rupture disc to move downward. The rupture disc may be shattered by contact with a surface on the lower tubular portion. Full casing internal diameter may be restored in the region where the rupture disc formerly sealed the casing.

What is claimed is: 
     
         1 . An apparatus for forming a buoyant chamber in a well, the apparatus comprising:
 (a) a first length of tubing operable to be positioned in the well and having an uphole end and a downhole end, the downhole end operable for connection to a second length of tubing, said second length of tubing comprising an apparatus operable for forming a lower boundary of a buoyant chamber;   (b) a rupture disc assembly disposed within the first length of tubing operable for forming an upper boundary of the buoyant chamber during deployment of the buoyant chamber into the well, the rupture disc assembly comprising a rupture disc held in a held position within the first length of tubing by a securing mechanism;   
       said rupture disc assembly operable to form and maintain a seal within said first length of tubing when said rupture disc is in said held position and when an upper surface of the rupture disc is subjected to a hydraulic pressure of a magnitude that is less than a threshold hydraulic pressure; 
       wherein the securing mechanism is operable to release in response to the upper surface of the rupture disc being subjected to a hydraulic pressure of a magnitude that is at least as high as the threshold hydraulic pressure; 
       wherein in operation, in response to the upper surface of the rupture disc being subjected to a hydraulic pressure of a magnitude that is at least as high as the threshold hydraulic pressure, the securing mechanism releases causing the rupture disc to move from the held position within the first length of tubing and break within the first length of tubing. 
     
     
         2 . An apparatus as claimed in  claim 1 , wherein the hydraulic pressure which the upper surface of the rupture disc is subjected to, that results in the securing mechanism releasing, is of a magnitude that is less than a rupture burst pressure of the rupture disc. 
     
     
         3 . An apparatus as claimed in  claim 1 , wherein the seal is a fluid tight seal. 
     
     
         4 . An apparatus as claim in  claim 1 , wherein the seal is maintained during at least part of the movement of the rupture disc within the first length of tubing. 
     
     
         5 . An apparatus as claimed in  claim 4 , wherein the seal is maintained during said movement of the rupture disc until the rupture disc breaks. 
     
     
         6 . An apparatus as claimed in  claim 1 , wherein in operation, the buoyant chamber comprises at least one of a buoyant liquid and a buoyant gas therein, such that, when the rupture disc breaks, the at least one of a buoyant liquid and a buoyant gas leaves the buoyant chamber. 
     
     
         7 . An apparatus as claimed in  claim 1 , wherein a region of the first length of tubing where the rupture disc is held in the held position has an enlarged cross-sectional area compared to a cross-sectional area of the second length of tubing. 
     
     
         8 . An apparatus as claimed in  claim 1 , wherein the rupture disc assembly comprises at least one seal member which assists in forming said seal. 
     
     
         9 . An apparatus as claimed in  claim 8 , wherein the rupture disc, the securing mechanism, and the at least one seal member together form said seal. 
     
     
         10 . An apparatus as claimed in  claim 9  wherein said at least one seal member comprises at least one o-ring. 
     
     
         11 . An apparatus as claimed in  claim 10  wherein said at least one seal member comprises a first seal member located between the securing mechanism and an inner wall surface of said first length of tubing, and a second seal member located between said securing mechanism and a surface of said rupture disc. 
     
     
         12 . An apparatus as claimed in  claim 11  wherein said second seal member is held in an annular groove in the outside surface of the rupture disc. 
     
     
         13 . An apparatus as claimed in  claim 1 , wherein the first length of tubing comprises a first region comprising a first internal surface having a first internal diameter and a second region comprising a second internal surface having a second internal diameter, wherein the first internal diameter is larger than the second internal diameter, wherein the rupture disc is held in the held position within the first region. 
     
     
         14 . An apparatus as claimed in  claim 13  wherein the first and second internal surfaces are cylindrical. 
     
     
         15 . An apparatus as claimed in  claim 1 , wherein an internal surface of the first length of tubing has a larger diameter than an internal surface of the second length of tubing. 
     
     
         16 . An apparatus as claimed in  claim 1  wherein the securing mechanism comprises a shear ring or a plurality of shear pins. 
     
     
         17 . An apparatus as claimed in  claim 16  wherein the shear ring comprises a plurality of bendable or shearable tabs arranged to seat the rupture disc in the held position. 
     
     
         18 . An apparatus as claimed in  claim 1  wherein the first length of tubing comprises at least two tubulars coupled together. 
     
     
         19 . An apparatus as claimed in  claim 1  wherein the apparatus operable for forming a lower boundary of a buoyant chamber comprises a float shoe. 
     
     
         20 . An apparatus for forming a buoyant chamber in a well, the apparatus comprising:
 (a) a first length of tubing operable to be positioned in the well and having an uphole end and a downhole end, the downhole end operable for connection to a second length of tubing, said second length of tubing comprising an apparatus operable for forming a lower boundary of a buoyant chamber;   (b) a rupture disc assembly disposed within the first length of tubing and operable for forming an upper boundary of the buoyant chamber, the rupture disc assembly comprising a rupture disc operable to be supported in a first position within the first length of tubing by a support structure;   
       said rupture disc assembly operable to provide said upper boundary of said buoyant chamber when said rupture disc is in said supported position within the first length of tubing; 
       wherein the support structure is operable to release in response to the upper surface of the rupture disc being subjected to a hydraulic pressure that is of a magnitude is at least as high as a threshold hydraulic pressure; 
       wherein in operation, in response to the upper surface of the rupture disc being subjected to a hydraulic pressure of a magnitude that is at least as high as the threshold hydraulic pressure and said magnitude being less than a rupture burst pressure of the rupture disc, the support structure releases causing the rupture disc to move from the first position within the first length of tubing and break within the first length of tubing. 
     
     
         21 . An apparatus as claimed in  claim 20  wherein the support structure comprises a shear ring, said shear ring comprising a plurality of bendable or shearable tabs arranged to support the rupture disc in the first position. 
     
     
         22 . An apparatus for forming a buoyant chamber in a well, the apparatus comprising:
 (a) a first length of tubing operable to be positioned in the well and having an uphole end and a downhole end, the downhole end operable for connection to a second length of tubing that comprises an apparatus operable for forming a lower boundary of a buoyant chamber;   (b) a rupture disc assembly disposed within the first length of tubing operable for forming an upper boundary of the buoyant chamber during deployment of the buoyant chamber into the well, the rupture disc assembly comprising a rupture disc held in a held position within the first length of tubing by a securing mechanism;   
       said rupture disc assembly operable to form and maintain a seal within said first length of tubing when said rupture disc is in said held position and when an upper surface of the rupture disc is subjected to a hydraulic pressure of a magnitude that is less than a threshold hydraulic pressure; 
       wherein the securing mechanism is operable to release in response to the upper surface of the rupture disc being subjected to a hydraulic pressure of a magnitude that is at least as large as the threshold hydraulic pressure; 
       wherein an internal surface of the first length of tubing has a larger diameter than an internal surface of the second length of tubing; 
       wherein in operation, in response to the upper surface of the rupture disc being subjected to a hydraulic pressure of a magnitude that is at least as large as the threshold hydraulic pressure, the securing mechanism releases causing the rupture disc to break within the first length of tubing. 
     
     
         23 . An apparatus as claimed in  claim 22  wherein the first and second internal surfaces are cylindrical. 
     
     
         24 . An apparatus as claimed in  claim 23 , wherein the hydraulic pressure which the upper surface of the rupture disc is subjected to, that results in the securing mechanism releasing, is less than a rupture burst pressure of the rupture disc. 
     
     
         25 . An apparatus as claimed in  claim 22 , wherein the seal is a fluid tight seal. 
     
     
         26 . An apparatus as claim in  claim 22 , wherein the seal is maintained during at least part of the movement of the rupture disc within the first length of tubing. 
     
     
         27 . An apparatus as claimed in  claim 26 , wherein the seal is maintained during said movement until the rupture disc breaks. 
     
     
         28 . An apparatus for forming a buoyant chamber in a well, the apparatus comprising:
 (a) a first length of tubing operable to be positioned in the well and having an uphole end and a downhole end, the downhole end operable for connection to a second length of tubing, said second length of tubing comprising a device operable for forming a lower boundary of a buoyant chamber; and   (b) a rupture disc disposed within the first length of tubing operable for forming an upper boundary of the buoyant chamber;   
       wherein the rupture disc is movable in an axial direction of the first length of tubing between:
 a first position, and 
 a second position axially downhole from the first position and within the first length of tubing, 
 
       wherein the rupture disc is supported by a support structure operable to support the rupture disc in the first position, 
       wherein the support structure is operable to release in response to hydraulic pressure being applied to an upper surface of the rupture disc of a magnitude that is at least as great as a threshold hydraulic pressure, and 
       wherein the rupture disc is operable to break upon moving from the first position and reaching the second position. 
     
     
         29 . An apparatus as claimed in  claim 28  wherein the rupture disc is operable to break upon impact when reaching the second position. 
     
     
         30 . An apparatus as claimed in  claim 28  wherein when the rupture disc is in said first position the rupture disc is spaced from a contact surface; and wherein when the rupture disc is in said second position, the rupture disc is in contact with the contact surface.