Spars are similar to TLPs in that both are platform structures that float vertically in the water, allowing production or drilling facilities to be installed. As with other floating production systems, components of a Spar include the hull, topside and mooring system.
Spars are most commonly used in the US Gulf of Mexico, due to their suitability for ultra-deepwater installation and access to the GOM pipeline network.
As of December 2019, 21 spars currently are in operation. Neptune, the first production Spar, was delivered in 1996 at a cost of $300 million and installed in 1,936 ft (590 m) of water. The most recent Spar, Aasta Hansteen, cost $2.6 billion, and when topsides are complete, will be installed by Equinor in 4,265 ft (1,300 m) of water in the Norwegian Sea. Perdido was installed by Shell in 8,005 ft (2,440 m) of water and currently is the deepest Spar installation.
Initially, Spars were designed with a full length cylinder exceeding 656 ft (200 m), three of these classic designs were built and installed: Neptune, Genesis, and Diana. Newer spars, called truss spars, no longer have a full length cylinder, but rather an upper hard tank and a lower truss structure.
Spars are extremely stable, making them suitable for drilling as well as production. Though no current installed units offer storage, Aasta Hansteen (topsides currently under construction) will have onboard storage capacity of 160,000 bbls.
Additional Spar strengths include minimum vertical movement, drilling capability, dry tree accommodation, and relative insensitivity to ultra-deepwater installation. However, Spars are expensive and require a horizontal tow for installation at destination. In addition, a heavy lift vessel or floatover crane vessel for hull/topside mating is necessary. Other drawbacks include minimal to zero storage and the Spar’s stacked deck design limits future flexibility.