A casing/liner string buoyancy arrangement including a casing/liner string, and a material defining a volume disposed within the string, the material excluding downhole fluids from the volume, the volume being of a lower specific gravity than the same downhole fluids. A method for managing buoyancy of a casing/liner string including configuring a casing/liner string, running the string, and selectively maintaining or degrading the material to adjust buoyancy of the string. A borehole system including a borehole in a subsurface formation, and an arrangement disposed in the borehole.