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Dynamic Positioning and Re-Entry. Schematic diagram showing general arrangements allowing positioning of the drilling vessel in deep water and technique of drill hole re-entry. The re-entry cone, on the sea floor, is 16 ft. in diameter and is mounted on steel casing in the upper part of the borehole, where it is inserted as the initial borehole is started. When the casing and core are fully in place, the assembly is detached from the drill string and the hole is drilled deeper. To change a bit, for example, the drill string is recovered to the ship, the bit is changed, and then again lowered to just above the cone. The vessel is moved as necessary to position the bit directly above the cone, as seen by side scanning sonar, at which time re-entry is made by lowering the pipe.

Dynamic Positioning and Re-Entry. Schematic diagram showing general arrangements allowing positioning of the drilling vess...