A buoyancy module assembly reduces the effective weight of a sub-sea conduit used in a deep-water wellbore drilling installation. The assembly includes a buoyant sleeve positioned around the conduit between upper and lower stop collar assemblies. The sleeve contains buoyant material forming most of its cross-section, with cross sectional segments thereof each encapsulated in a non-porous resinous material that forms an outer jacket around each segment. In one embodiment, a non-rotating generally circular inside diameter of the sleeve is formed by the thin layer of jacket material bonded directly to an interior reinforcing cage. A narrow gap is formed between the ID of the non-rotating sleeve and the OD of the conduit. The collar assemblies comprise an inner collar rigidly affixed to the conduit and contained within a larger diameter outer shell adapted for rotation relative to the fixed inner collar.