What is a Spar?

Spar platforms are among the largest offshore platforms in use.

While tension leg platforms have been a reliable concept for Shell's current Gulf of Mexico developments, the ultra-deepwater environment and the need for a low-cost platform for drilling led to the selection of a spar for the Perdido development. This will be Shell's first spar concept in the Gulf.

Named for logs used as buoys in shipping and moored in place vertically, spar platforms are among the largest offshore platforms in use. Perdido, a truss spar, consists of a large-diameter, single vertical cylinder supporting a deck with an open truss with a hard tank bottom.

The spar does not extend all the way to the seafloor, but instead is tethered to the bottom by a series of cables and lines. This large cylinder helps stabilize the platform in the water, and allows for movement to absorb the force of a potential hurricane.

Shell considered several production and export systems alternatives, but in the end decided on the spar concept for a number of reasons, including:

• the desire to have a high well count with full drilling, completion and sidetracking capability from a low-cost platform drilling rig and
• the existence of a significant pipeline transportation network in the area with available capacity.

The deep draft nature of a spar design makes it inherently more stable than other designs. It is also simpler to maintain stability during producing operations, with little or no active ballast control required.

The first spar platform in the GOM was installed in September of 1996, with a cylinder measuring 705 feet long and 72 feet in diameter. The platform operated in 1,930 feet of water.

The current water depth record for a Spar host is 5,610 feet for Dominion's Devil's Tower spar, located on Mississippi Canyon Block 773. Perdido’s hull is 550 ft long and 118 feet in diameter and will be located in a water depth slightly greater then 7,800 feet.

The deepest floating production system in the world is the Independence Hub semi host located on Mississippi Canyon Block 920 in a water depth of 7,920 feet.