Moving an Oil Rig
Oil rigs are impressive structures to behold. They can be hundreds of metres tall and weigh hundreds of thousands of tons, so it’s intriguing that these ocean monstrosities are designed to be mobile. Although many can be driven and tugged by boats, there are some special considerations to be taken into account.
Oil rigs have to be mobile, particularly any containing drilling equipment. It wouldn’t make sense for a drilling unit to be permanent, although semi-permanent production platforms are possible. Yet, how do you move these giant structures? It takes teams of specialist engineers and marine scientists to coordinate the logistics of these moves. Not to mention each type of rig has a different mobility method.
Swamp barges, most common in the southern states of the USA such as Louisiana, are used in water that is only 5-10ft deep. They drive and function like a normal swamp barge, and once they reach their location are just ballasted down. When it’s time to move location, off they sail. Drill ships are another key mobile oil rig, but are best used in deep water. They are fully mobile and rotational, much like normal ships. As a result, they’re nice and simple to move. But, these rigs aren’t much in comparison to the large ocean rigs.
Shallow water jack-up rigs appear to be the current oil rig of choice for drilling companies. Maersk have just unveiled the first of four brand new jack up rigs costing around $2.6bn in total. Aqualis CEO David Wells has labeled jack-up rigs as the most challenging type of rig to move, very much due to the fact that they stand on the seabed. As a result, there has to be a lot of research into the type of soils on the seabed. If the surface soil is hard with soft soil underneath, then the rig can collapse quickly in a process known as ‘punchthrough’. This can lead to broken equipment and even the legs of the rig breaking. Before being put into place, the rig, like all other types, is towed, but this is a very slow process dependant on its size and weight. It would be rare for speeds to go above 5 knots.
Semi submersible rigs are fully floating, used in waters with depths of up to 8000ft. These can be dynamically positioned with a series of thrusters that will maintain their position. Semi-submersibles are complicated bits of marine engineering; they are able to be raised in and out of the water to reduce hull drag and then lowered again to alter the centre of buoyancy, but this must always be above the centre of mass.
Maths, mechanics, marine science and a lot of planning is essential when moving oil rigs. They’re giants of the sea that require a lot of patience and expertise already, and they’re only getting bigger.