US Patent 10989013 Buoyancy assist tool with center diaphragm debris barrier

A downhole apparatus comprises a casing string with a removable plug therein to block flow therethrough. A flow barrier is positioned in the casing below the removable plug and the removable plug and the flow barrier defining a buoyancy chamber therebetween. A debris barrier positioned above the removable plug comprises a rigid annular ring with a flexible diaphragm covering the center opening defined by the annular ring.