US Patent 11293260 Buoyancy assist tool

A buoyancy assist tool has an outer case and a rupture disk connected in the outer case. A sleeve is disposed in the outer case and movable from first to second position in the outer case. A rupture disk membrane of a rupture disk prevents the sleeve from moving to the second position prior to the rupture disk membrane rupturing. The outer case is configured to be connected in a well casing. A lock ring holds the sleeve in the first position.