A drilling, production and oil storage caisson for use in deep water offshore well operations in which the caisson has such a deep draft that its bottom end is subject only to minimal excitation forces caused by wave, wind and current acting on the caisson, the caisson including a plurality of oil storage compartments, a plurality of water ballast compartments above said oil storage compartments, a through axial passageway through said compartments; a riser system including a plurality of riser pipes in concentric circular arrangement within the through passageway or center well, each of the riser pipes being supported and tensioned by a buoyant flotation unit connected thereto; a drill string extending axially through said passageway between said riser pipes; and mooring lines connected to the bottom portion of the caisson extending therefrom with relatively low scope of 1:1 or less and providing a small watch circle for anchors for said mooring lines, the mooring lines being tensioned so that the mooring lines are substantially straight. A counterbalance for the drilling string includes a weighted section located near the bottom of the caisson. A deep draft caisson constructed and arranged so that heave motions are minimal.