Mr Charlie, the first mobile drilling unit to drill offshore in 1954, was a submersible unit. The first semi-submersible, Blue Water Rig 1 arrived by accident in 1961. Blue Water Drilling Company owned and operated the four column submersible drilling rig Blue Water Rig No.1 in the Gulf of Mexico for Shell Oil Company. The offshore drilling rig was built at Ingalls shipyard in Pescagoula in 1957.
Starting operations in the Gulf of Mexico it quickly appeared that the pontoons were not sufficiently buoyant to support the weight of the rig and its consumables. Offloading the vessel was time consuming and expensive. Taking into account this specific situation, it was decided to tow the submersible rig between locations at a draught midway between the top of the pontoons and the underside of the deck. As, it was It was observed that the motions at this draught were very small, and Blue Water Drilling and Shell jointly decided that the rig could be operated in the floating mode. In January 1962, Blue Water Rig 1 spud a record-setting offshore well in 297 ft of water in the Gulf of Mexico. This was at least three times deeper than wells drilled by other mobile drilling vessels, such as submersibles and jackups. Outside observers tried to figure out how the Blue Water 1 could remain nearly motionless in those depths on the open seas. Several competitors spied from helicopters and workboat but did not find any valid answer.
A few months later, in August 1962, Shell Oil disclosed the details of its new floating drilling rig. With an eight-anchor mooring system the converted submersible was equipped to operate in 600 ft without resting on the bottom.
With Blue Water 1, Shell paved the way for future deepwater development.
The first purpose built drilling semi-submersible Ocean Driller was launched in 1963. By 1972, there were 30 semi-submersible units in operation.
(Image: Blue Water Rig 1/Friede & Goldman)