How Do Spars Work?
A floating platform alternative that can support drilling, production and storage operations, the spar consists of a large vertical cylinder bearing topsides with equipment. Similar to an iceberg, the majority of a spar facility is located beneath the water's surface, providing the facility increased stability.
Mad Dog Spar
Originally designed as a floating buoy to acquire oceanographic information, the main component of a spar facility is the deep-draft floating chamber, or hollow cylindrical hull. Characteristically, the hull is encircled with spiraling strakes to add stability. Additionally, the bottom of the cylinder includes a ballasting section with material that weighs more than water, ensuring the center of gravity is located below the center of buoyancy.
The deep-draft design makes the spar less affected by wind, wave and currents, enabling the facility to support both subsea and dry tree developments. Additionally, the enclosed cylinder acts as protection for risers and equipment, making spars an ideal choice for deepwater developments. Furthermore, the hull can provide storage for produced oil or gas.
Atop the spar hull sits the topsides, which can be comprised of drilling equipment, production facilities and living quarters. Drilling is performed from the topsides through the hollow cylinder hull; and drilling, import/export and production risers are passed through the enclosed hull, as well. The whole spar facility is then moored to the seafloor.
While the hull is fastened to the sea bed through various mooring techniques, spar facilities do not require moorings to stay upright. The unique design of the spar ensures that the facility will not topple even if the moorings are not connected because the center of gravity is located below the center of buoyancy.
Types of Spars
There are three types of spars, including the original spar design, truss spars and cell spars. Consisting of a single cylindrical hull, the original design for spars was created in the mid '90s with the first developed for the Neptune field in the Gulf of Mexico.
The next rendition of the spar was the truss spar, which is similar to the original spar design, but the cylindrical hull is shorted and a truss is incorporated below it. The truss usually includes horizontal plates that help to decrease vertical movement. The truss spar is advantageous because it weighs less than the original design, and because it requires less steel, which costs less.
Red Hawk Cell Spar
The most recent variation of the spar is the cell spar, which is a scaled-down version of the original design. The cell spar includes six pressure vessels gathered around a seventh vessel. Resembling massive hot dogs, these pressure vessels are more easily and cost-effectively generated through mass production. Providing the buoyancy for the facility, the vessels are held in place by structural steel, which extends below the vessels and keeps with the deep-draft design by providing stability.