(57) A submerged tubular tower (10) (see Fig. 1) is connected at its lower end (15) to
an ocean floor (11) at a site where at least one subsea hydrocarbon well is to be
drilled. A riser duct (22) (see Fig. 5) for each well to be drilled extends from an
upwardly accessible connection point (20) at the upper end (14) of the tower to the
lower end of the tower. The tower is positively buoyant to stand erect in an unguyed
manner. The upper end (18) of the tower is located a substantial distance above the
ocean floor at a depth sufficiently small to enable wells to be drilled through the
riser ducts, through equipment (19) landed on the top of the tower, using floating
drilling equipment (12) designed for use in substantially shallower water depths.
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