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Fixed platforms are permanent structures for offshore oil drilling, raised above the sea surface by steel or concrete supports. They are limited to shallow water and attached to the ocean floor by jackets. The working space is made up of bridges built in shipyards and can pump oil directly to onshore storage or use storage tanks located below the waterline. The first productive offshore oil wells were drilled in Ohio in 1891, and the first fixed platform drilling platform out of sight of land was built in the Gulf of Mexico in 1947.
A fixed platform is a permanent structure attached to the ocean floor, often for the purpose of offshore oil drilling. Most of the working space of such a platform is raised above the sea surface by rigid steel or concrete supports. This distinguishes a fixed platform from mobile platforms, which float on the sea surface and are anchored to the ocean floor by more or less flexible moorings. Fixed platforms are typically installed in water depths less than 1,700 feet (520 meters), with deeper drilling operations requiring more complex mobile platforms.
The first productive offshore oil wells were drilled in Ohio’s Grand Lake St. Marys State Park in 1891, using fixed platforms set on wooden piles on the lake bed. In 1947, the first fixed platform drilling platform located out of sight of land was built in the Gulf of Mexico. Fixed platforms were the most common method of offshore drilling for most of the 20th century, although the first mobile drilling rigs were operational in the early 1920s. Due to their high degree of stability, depth limitation, and high cost, modern fixed platform drilling rigs are limited to long-term drilling operations in shallow water.
Fixed platforms are directly attached to the ocean floor by structural support known as a jacket. Early jackets were made of concrete piles, while modern deep-water jackets are complex tubular steel support towers. The base of a jacket can be several times wider than the top, and are often driven deep into the mud of the ocean floor for support. The jackets are partially or entirely built ashore and shipped to the platform on barges towed by tugboats. Once there, they are lowered to the ocean floor with the help of ROVs and driven into position using barge-mounted pile drivers.
The bridges that make up the working space of a platform are usually built in shipyards or sheltered bays. While early bridges were towed into place on barges, many modern bridges are built to float in transit. They are lifted to the top of the waiting jacket using hydraulic jack systems or crane barges and are usually positioned high enough above the waterline to avoid all but the largest waves. The decks can be up to 200 feet (60 meters) wide and consist of multiple levels of work and living areas.
If a fixed platform is near shore, it can pump oil directly from the drill site to onshore storage facilities through pipelines laid along the ocean floor. In the case of above ground drilling operations, the platform must include large storage tanks that hold the oil until it can be transferred to an oil tanker. Storage tanks are often located below the waterline, where they act as ballast to help the platform resist the force of waves and currents.
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