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 configured for connection in-line with the casing string and (ii) a rupture disc having a rupture burst pressure and in sealing engagement with a region of the tubular member within the upper and lower ends,wherein the rupture disc is configured to disengage from sealing engagement when exposed to a pressure greater than a hydraulic pressure in the casing string after the casing string has been positioned in the wellbore and the region of the tubular member where the rupture disc is attached has a larger internal diameter than the internal diameter of the casing string and is parallel to the internal diameter of the casing string. view more

The float tool recited in claim 28 wherein the rupture disc is further configured to rupture when exposed to a rupturing force greater than the rupture burst pressure and the pressure greater than the hydraulic pressure is less than the rupture burst pressure. view more

The float tool recited in claim 28 wherein the rupture disc forms an upper seal of a sealed chamber.

The float tool recited in claim 36 wherein the sealed chamber is filled with a fluid having a lower specific gravity than that of the well fluid.

A method for installing casing in a wellbore containing a well fluid and having an upper vertical portion, a lower horizontal portion, and a bend portion connecting the upper and lower portions, the method comprising:running a casing string into the wellbore, 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 upper and lower portions of the casing string separated by a chamber sealed on one end by a rupture disc assembly and on an opposing end by a seal, the chamber containing a first fluid having a first specific gravitywherein the rupture disc assembly comprises (i) a tubular member having an upper end and a lower end, the upper and lower ends connected in-line with the casing string and (ii) a rupture disc having a rupture burst pressure and in sealing engagement with a region of the tubular member within the upper and lower ends,wherein the rupture disc is configured to disengage from sealing engagement when exposed to a pressure greater than a hydraulic pressure in the casing string after the casing string has been positioned in the wellbore and the region of the tubular member where the rupture disc is attached has a larger internal diameter than the internal diameter of the casing string and is parallel to the internal diameter of the casing string; andfloating at least a portion of the casing string containing the sealed chamber in the well fluid in the lower horizontal portion of the wellbore. view more

The method recited in claim 50 further comprising:filling the casing string above the rupture disc assembly with a second fluid having a second specific gravity higher than the first specific gravity.

The method recited in claim 51 wherein the first specific gravity is less than a specific gravity of the well fluid.

The method recited in claim 50 further comprising applying a pressure within the casing string greater than the hydraulic pressure in the casing string to disengage the rupture disc from sealing engagement.

The method recited in claim 55 wherein the rupture disc is further configured to rupture when exposed to a rupturing force greater than the rupture burst pressure and the pressure greater than the hydraulic pressure is less than the rupture burst pressure. view more

The method recited in claim 56 further comprising applying a rupturing force to rupture the rupture disc.