US Patent 11293261 Buoyancy assist tool

A buoyancy assist tool has an outer case and a sleeve disposed in the outer case. The sleeve is movable from first to second positions in the outer case. A permeable membrane is attached to the movable sleeve at a lower end thereof. A rupture disk is mounted in the outer case. Fluid flow through the permeable membrane detaches the sleeve from the outer case and moves the sleeve from the first to the second position. In the second position, the sleeve creates an open bore for the passage of downhole tools therethrough.