Casing float tool

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 up-hole end and a downhole end, the downhole end operable for connection to a second length of tubing that comprises a float device 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, the rupture disc assembly comprising:
• a rupture disc held in sealing engagement within the first length of tubing by a securing mechanism, the securing mechanism being operable to release in response to a threshold hydraulic pressure being applied to an upper surface of the rupture disc that is less than a rupture burst pressure of the rupture disc, and wherein in operation, in response to application of an activating hydraulic pressure to the upper surface of the rupture disc that is at least as great as the threshold hydraulic pressure and less than the rupture burst pressure, the securing mechanism releases causing the rupture disc to move within the first length of tubing and break within the first length of tubing wherein when the rupture disc is in sealing engagement within the first length of tubing, a first seal is provided between the rupture disc and the securing mechanism and a second seal is provided between the securing mechanism and an inner surface of the first length of tubing, to thereby provide the upper boundary of the buoyant chamber.

A float tool configured for use in positioning a casing string in a wellbore containing a well fluid, the casing string having an internal diameter that defines a fluid passageway between an upper portion of the casing string and a lower portion of the casing string, the float tool comprising:

• a rupture disc assembly comprising:
• (i) a tubular member having an upper end and a lower end, the upper and lower ends operable for connection in-line with the casing string;
• and (ii) a rupture disc having a rupture burst pressure, and said rupture disc operable to be in sealing engagement within a region of the tubular member;
• wherein the rupture disc assembly is operable to change from a stationary sealing mode wherein the rupture disc is in sealing engagement to provide an upper seal of a sealed buoyant chamber during deployment of the casing string with the float tool into the wellbore, to a rupture disc breaking mode wherein the rupture disc moves within the tubular member and is broken within the tubular member, when the rupture disc is exposed to an activating hydraulic pressure greater than a hydraulic pressure in the casing string after the casing string has been positioned in the wellbore.