There are disclosed two embodiments of a subsea drilling, completion and/or workover apparatus which includes a spar buoy having a well therethrough, and a riser which extends through the well in the buoy for connection to the subsea wellhead during the drilling and/or completion process. A buoyancy tank is disposed about the riser within the buoy well to support the riser, and the upper end of the tank is fee to move vertically with respect to the well deck so that it will not be placed in compression despite anticipated rise and fall of the buoyancy tank.